Roblox backend: window content in its own clipped layer at the scroll origin (scrolling moves pixels instead of redrawing), 128px tiles

build/ImGui.linemap.json

@@ -1 +1 @@
-[[12, "imgui.lua"], [13795, "imgui_demo.lua"], [14728, "imgui_demo_2.lua"], [17803, "imgui_demo_apps.lua"], [19062, "imgui_demo_tools.lua"], [20388, "imgui_demo_widgets.lua"], [22312, "imgui_docking.lua"], [25440, "imgui_dragdrop.lua"], [25732, "imgui_draw.lua"], [30979, "imgui_h.lua"], [33153, "imgui_impl_roblox.lua"], [34140, "imgui_impl_roblox_fonts.lua"], [40543, "imgui_internal.lua"], [43715, "imgui_tables.lua"], [48062, "imgui_tabs.lua"], [49229, "imgui_widgets.lua"], [57763, "imstb_rectpack.lua"], [58209, "imstb_textedit.lua"], [59450, "imstb_truetype.lua"], [61918, "imstd_minstdio.lua"]]
+[[12, "imgui.lua"], [13799, "imgui_demo.lua"], [14732, "imgui_demo_2.lua"], [17807, "imgui_demo_apps.lua"], [19066, "imgui_demo_tools.lua"], [20392, "imgui_demo_widgets.lua"], [22316, "imgui_docking.lua"], [25444, "imgui_dragdrop.lua"], [25736, "imgui_draw.lua"], [30984, "imgui_h.lua"], [33158, "imgui_impl_roblox.lua"], [34231, "imgui_impl_roblox_fonts.lua"], [40634, "imgui_internal.lua"], [43806, "imgui_tables.lua"], [48153, "imgui_tabs.lua"], [49320, "imgui_widgets.lua"], [57854, "imstb_rectpack.lua"], [58300, "imstb_textedit.lua"], [59541, "imstb_truetype.lua"], [62009, "imstd_minstdio.lua"]]

build/ImGui.luau

@@ -7161,6 +7161,10 @@ function ImGui.Begin(name, open, flags)
 
     if bit32.band(flags, ImGuiWindowFlags.DockNodeHost) == 0 and not window.SkipRefresh then
         ImGui.PushClipRect(window.InnerClipRect.Min, window.InnerClipRect.Max, true)
+        -- [Roblox backend] content clip + scroll origin: lets the backend move scrolled content instead of redrawing it
+        local dl, cr = window.DrawList, window.DrawList._CmdHeader.ClipRect
+        dl._ContentClipX0, dl._ContentClipY0, dl._ContentClipX1, dl._ContentClipY1 = cr.x, cr.y, cr.z, cr.w
+        dl._ScrollOriginX, dl._ScrollOriginY = window.Pos.x - window.Scroll.x, window.Pos.y - window.Scroll.y
     end
 
     window.WriteAccessed = false
@@ -28889,6 +28893,7 @@ end
 
 -- TODO:
 function MT.ImDrawList:_ResetForNewFrame()
+    self._ContentClipX0 = nil -- set again by Begin() (Roblox backend scroll reuse)
     if self._Splitter._Count > 1 then
         self._Splitter:Merge(self)
     end
@@ -33573,7 +33578,7 @@ end
 -- relative to the layer's origin (top-left of its content). Primitives are hashed into tiles in layer-relative
 -- coordinates, so moving a window only moves its Frame: no tile changes, nothing re-rasterized or uploaded.
 -- Only tiles whose hash changed are redrawn; the hash covers everything that affects a tile's pixels.
-local TILE = 256
+local TILE = 128
 TILE_SIZE = Vector2.new(TILE, TILE)
 local P1, P2 = 2147483647, 2147483629 -- two independent 31 bit hashes per tile (collision odds ~2^-62)
 local KEY_W = 64 -- tile key = ty * KEY_W + tx (layers up to 16384 px wide)
@@ -33585,6 +33590,8 @@ local pr_a, pr_b, pr_c, pr_d, pr_t, pr_g = {}, {}, {}, {}, {}, {} -- vertices (p
 local pr_cx0, pr_cy0, pr_cx1, pr_cy1 = {}, {}, {}, {}  -- clip (screen pixels)
 local pr_bx0, pr_by0, pr_bx1, pr_by1 = {}, {}, {}, {}  -- clipped bounds (screen pixels)
 local pr_tex = {}                                      -- texture id
+local pr_k = {}                                        -- layer kind (1..3)
+local plist1, plist2, plist3 = {}, {}, {}              -- primitive indices per layer kind
 
 @native
 local function HashVertex(h1, h2, v, ox, oy)
@@ -33647,22 +33654,43 @@ local function DrawRectGradient(x0, y0, x1, y1, ca, cb, kind, t, u, v, cx0, cy0,
     end
 end
 
-local function GetLayer(bd, draw_list)
+-- Layer kinds per draw list: 1 = drawn before the window content (background, title bar, borders, scrollbar),
-    local layer = bd.Layers[draw_list]
+-- 2 = window content (positioned at the scroll origin inside a ClipsDescendants frame, so scrolling just moves it),
-    if layer then return layer end
+-- 3 = anything not clipped to the content drawn after content started (menu bar, overlays). Stacked 1 < 2 < 3.
+local function NewFrame(parent, clips)
     local frame = Instance.new("Frame")
     frame.Name = "Layer"
     frame.BackgroundTransparency = 1
     frame.BorderSizePixel = 0
     frame.Size = UDim2.fromOffset(0, 0)
+    frame.ClipsDescendants = clips
     frame.Visible = false
-    frame.Parent = bd.Gui
+    frame.Parent = parent
-    layer = { Frame = frame, Tiles = {}, TH1 = {}, TH2 = {}, TN = {}, TL = {}, Touched = {}, NTouched = 0,
+    return frame
-              Visible = false, X = false, Y = false, Z = -1, LastUsed = 0 }
+end
-    bd.Layers[draw_list] = layer
+
+local function GetLayer(bd, draw_list, kind)
+    local set = bd.Layers[draw_list]
+    if not set then set = { LastUsed = 0 }; bd.Layers[draw_list] = set end
+    local layer = set[kind]
+    if layer then return layer end
+    local root, frame
+    if kind == 2 then
+        root = NewFrame(bd.Gui, true)
+        frame = NewFrame(root, false); frame.Visible = true
+    else
+        frame = NewFrame(bd.Gui, false); root = frame
+    end
+    layer = { Root = root, Frame = frame, Tiles = {}, TH1 = {}, TH2 = {}, TN = {}, TL = {}, TX = {}, TY = {}, Touched = {}, NTouched = 0,
+              Visible = false, X = false, Y = false, Z = -1, CX0 = false, CY0 = false, CX1 = false, CY1 = false }
+    set[kind] = layer
     return layer
 end
 
+local function HideLayer(layer)
+    if layer.Visible then layer.Visible = false; layer.Root.Visible = false end
+end
+
 local function GetTile(bd, layer, key, tx, ty)
     local tile = layer.Tiles[key]
     if tile then return tile end
@@ -33685,13 +33713,18 @@ local function GetTile(bd, layer, key, tx, ty)
     return tile
 end
 
-local function DestroyLayer(layer)
+local function DestroyLayerSet(set)
+    for kind = 1, 3 do
+        local layer = set[kind]
+        if layer then
             for _, tile in pairs(layer.Tiles) do tile.Image:Destroy() end
-    layer.Frame:Destroy()
+            layer.Root:Destroy()
+        end
+    end
 end
 
 local function DestroyTiles(bd)
-    for _, layer in pairs(bd.Layers) do DestroyLayer(layer) end
+    for _, set in pairs(bd.Layers) do DestroyLayerSet(set) end
     bd.Layers = {}
 end
 
@@ -33702,134 +33735,15 @@ local function PB(name) if profiling then profilebegin(name) end end
 local function PE() if profiling then profileend() end end
 
 @native
-function ImGui_ImplRoblox_RenderDrawData(draw_data)
+local function DrawLayer(bd, layer, plist, np, lx0, ly0, ox, oy, force, z, clip_x0, clip_y0, clip_x1, clip_y1)
-    local bd = ImGui_ImplRoblox_GetBackendData()
-    PB("ImGui RenderDrawData")
-
-    PB("ImGui textures")
-    if draw_data.Textures ~= nil then
-        for _, tex in draw_data.Textures:iter() do
-            if tex.Status ~= ImTextureStatus.OK then
-                ImGui_ImplRoblox_UpdateTexture(tex)
-                bd.ForceRedraw = true -- texture contents changed: tiles sampling it must be redrawn
-            end
-        end
-    end
-    PE()
-
-    -- Render rate cap: textures are always updated (imgui expects it), tiles only at bd.RenderRate Hz
-    -- Optional lower cap while scrolling / resizing / moving a window (SetBusyRenderRate, off by default)
-    local rate = bd.RenderRate
-    if bd.BusyRenderRate > 0 then
-        local g = ImGui.GetCurrentContext()
-        local busy = g.WheelingWindow ~= nil or g.MovingWindow ~= nil -- (io.MouseWheel is already cleared by EndFrame)
-        if not busy and g.ActiveId ~= 0 then
-            local w = g.ActiveIdWindow
-            local cur = g.MouseCursor -- ResizeAll..ResizeNWSE while a resize grip/border is held
-            busy = (cur >= ImGuiMouseCursor.ResizeAll and cur <= ImGuiMouseCursor.ResizeNWSE)
-                or (w ~= nil and (g.ActiveId == ImGui.GetWindowScrollbarID(w, ImGuiAxis.X) or g.ActiveId == ImGui.GetWindowScrollbarID(w, ImGuiAxis.Y)))
-        end
-        if busy and (rate <= 0 or bd.BusyRenderRate < rate) then rate = bd.BusyRenderRate end
-    end
-    if rate > 0 then
-        local now = os.clock()
-        if now + 0.002 < bd.NextRender then PE(); return end
-        bd.NextRender = math.max(bd.NextRender + 1 / rate, now)
-    end
-
-    local sw, sh = floor(draw_data.DisplaySize.x), floor(draw_data.DisplaySize.y)
-    if sw <= 0 or sh <= 0 then PE(); return end
-    local ox, oy = draw_data.DisplayPos.x, draw_data.DisplayPos.y
-    local lim_x0, lim_y0, lim_x1, lim_y1 = -CLIP_PAD, -CLIP_PAD, sw + CLIP_PAD, sh + CLIP_PAD
-    bd.FrameNo += 1
-    local frame_no = bd.FrameNo
-    local force = bd.ForceRedraw
-    bd.ForceRedraw = false
     local scale = bd.Scale
-
-    local n = 0
-    local z = 0
-    for _, draw_list in draw_data.CmdLists:iter() do
-        -- Pass 1: collect this list's primitives and their bounds
-        PB("ImGui collect")
-        local first = n + 1
-        local lx0, ly0 = math.huge, math.huge
-        local vtx, idx = draw_list.VtxBuffer.Data, draw_list.IdxBuffer.Data
-        for _, pcmd in draw_list.CmdBuffer:iter() do
-            if pcmd.UserCallback ~= nil then
-                pcmd.UserCallback(draw_list, pcmd)
-            elseif pcmd.ElemCount > 0 then
-                local clip = pcmd.ClipRect
-                local cx0, cy0 = max(floor(clip.x - ox), lim_x0), max(floor(clip.y - oy), lim_y0)
-                local cx1, cy1 = min(floor(clip.z - ox), lim_x1), min(floor(clip.w - oy), lim_y1)
-                if cx1 > cx0 and cy1 > cy0 then
-                    local tex_id = pcmd:GetTexID()
-                    local t = bd.Textures[tex_id]
-                    local vo = pcmd.VtxOffset
-                    local i, last = pcmd.IdxOffset + 1, pcmd.IdxOffset + pcmd.ElemCount
-                    while i <= last do
-                        local ia, ic = idx[i], idx[i + 2]
-                        local va, vb, vc = vtx[vo + ia], vtx[vo + idx[i + 1]], vtx[vo + ic]
-                        local vd = false
-                        local gk = false
-                        local pa, pb, pc = va[1], vb[1], vc[1]
-                        local bx0, by0, bx1, by1
-                        if i + 5 <= last and idx[i + 3] == ia and idx[i + 4] == ic then
-                            local d = vtx[vo + idx[i + 5]]
-                            local pd = d[1]
-                            -- axis aligned quad (TL, TR, BR, BL)
-                            if pa.y == pb.y and pb.x == pc.x and pc.y == pd.y and pd.x == pa.x and pa.x < pb.x and pa.y < pd.y then
-                                local col = va[3]
-                                local ta, tb, tc, td = va[2], vb[2], vc[2], d[2]
-                                if vb[3] == col and vc[3] == col and d[3] == col then
-                                    if tb.x == tc.x and tb.y == ta.y and td.x == ta.x and td.y == tc.y then vd = d end
-                                elseif ta.x == tb.x and ta.x == tc.x and ta.x == td.x and ta.y == tb.y and ta.y == tc.y and ta.y == td.y then
-                                    -- constant uv, linear gradient: vertical (top/bottom pairs equal) or horizontal (left/right pairs equal)
-                                    if vb[3] == col and d[3] == vc[3] then vd = d; gk = 1
-                                    elseif d[3] == col and vb[3] == vc[3] then vd = d; gk = 2 end
-                                end
-                                if vd then
-                                    bx0, by0 = ceil(pa.x - ox - 0.5), ceil(pa.y - oy - 0.5)
-                                    bx1, by1 = ceil(pc.x - ox - 0.5), ceil(pc.y - oy - 0.5)
-                                end
-                            end
-                        end
-                        if vd then
-                            i = i + 6
-                        else
-                            bx0, by0 = floor(min(pa.x, pb.x, pc.x) - ox), floor(min(pa.y, pb.y, pc.y) - oy)
-                            bx1, by1 = ceil(max(pa.x, pb.x, pc.x) - ox) + 1, ceil(max(pa.y, pb.y, pc.y) - oy) + 1
-                            i = i + 3
-                        end
-                        if bx0 < cx0 then bx0 = cx0 end
-                        if by0 < cy0 then by0 = cy0 end
-                        if bx1 > cx1 then bx1 = cx1 end
-                        if by1 > cy1 then by1 = cy1 end
-                        if bx0 < bx1 and by0 < by1 then
-                            n = n + 1
-                            pr_a[n], pr_b[n], pr_c[n], pr_d[n], pr_t[n], pr_g[n], pr_tex[n] = va, vb, vc, vd, t, gk, tex_id
-                            pr_cx0[n], pr_cy0[n], pr_cx1[n], pr_cy1[n] = cx0, cy0, cx1, cy1
-                            pr_bx0[n], pr_by0[n], pr_bx1[n], pr_by1[n] = bx0, by0, bx1, by1
-                            if bx0 < lx0 then lx0 = bx0 end
-                            if by0 < ly0 then ly0 = by0 end
-                        end
-                    end
-                end
-            end
-        end
-        PE()
-
-        local layer = GetLayer(bd, draw_list)
-        layer.LastUsed = frame_no
-        if n < first then
-            if layer.Visible then layer.Visible = false; layer.Frame.Visible = false end
-        else
     -- Pass 2: hash primitives into layer-relative tiles
     PB("ImGui tile hash")
     local th1, th2, tn, tl, touched = layer.TH1, layer.TH2, layer.TN, layer.TL, layer.Touched
     for k = 1, layer.NTouched do tn[touched[k]] = 0 end
     local nt = 0
-            for p = first, n do
+    for pi = 1, np do
+        local p = plist[pi]
         local tex_id = pr_tex[p]
         -- The clip rect only affects pixels inside the primitive's bounds, so hash the clipped bounds (relative)
         -- instead of the clip itself: a window clipped by the (fixed) viewport rect stays hash-stable when moved.
@@ -33852,6 +33766,7 @@ function ImGui_ImplRoblox_RenderDrawData(draw_data)
                     if not tl[key] then tl[key] = {} end
                     nt = nt + 1
                     touched[nt] = key
+                    layer.TX[key], layer.TY[key] = tx, ty
                 end
                 k = k + 1
                 tn[key] = k
@@ -33865,14 +33780,25 @@ function ImGui_ImplRoblox_RenderDrawData(draw_data)
     PE()
 
     -- Place the layer (this is all a window move costs)
-            local frame = layer.Frame
+    local root = layer.Root
+    if root ~= layer.Frame then
+        -- content: clip frame at the content clip rect, tiles frame at the scroll origin relative to it
+        if layer.CX0 ~= clip_x0 or layer.CY0 ~= clip_y0 or layer.CX1 ~= clip_x1 or layer.CY1 ~= clip_y1 then
+            layer.CX0, layer.CY0, layer.CX1, layer.CY1 = clip_x0, clip_y0, clip_x1, clip_y1
+            root.Position = UDim2.fromOffset(clip_x0 / scale, clip_y0 / scale)
+            root.Size = UDim2.fromOffset((clip_x1 - clip_x0) / scale, (clip_y1 - clip_y0) / scale)
+            layer.X = false
+        end
         if layer.X ~= lx0 or layer.Y ~= ly0 then
             layer.X, layer.Y = lx0, ly0
-                frame.Position = UDim2.fromOffset(lx0 / scale, ly0 / scale)
+            layer.Frame.Position = UDim2.fromOffset((lx0 - clip_x0) / scale, (ly0 - clip_y0) / scale)
         end
-            z = z + 1
+    elseif layer.X ~= lx0 or layer.Y ~= ly0 then
-            if layer.Z ~= z then layer.Z = z; frame.ZIndex = z end
+        layer.X, layer.Y = lx0, ly0
-            if not layer.Visible then layer.Visible = true; frame.Visible = true end
+        root.Position = UDim2.fromOffset(lx0 / scale, ly0 / scale)
+    end
+    if layer.Z ~= z then layer.Z = z; root.ZIndex = z end
+    if not layer.Visible then layer.Visible = true; root.Visible = true end
 
     -- Pass 3: redraw + upload changed tiles, hide unused ones
     PB("ImGui raster+upload")
@@ -33884,8 +33810,7 @@ function ImGui_ImplRoblox_RenderDrawData(draw_data)
     for kk = 1, nt do
         local key = touched[kk]
         local count = tn[key]
-                local tx, ty = key % KEY_W, floor(key / KEY_W)
+        local tx, ty = layer.TX[key], layer.TY[key]
-                if tx < 0 then tx = tx + KEY_W; ty = ty - 1 end
         local tile = GetTile(bd, layer, key, tx, ty)
         if force or tile.H1 ~= th1[key] or tile.H2 ~= th2[key] then
             tile.H1, tile.H2 = th1[key], th2[key]
@@ -33952,14 +33877,180 @@ function ImGui_ImplRoblox_RenderDrawData(draw_data)
     end
     PE()
 end
+
+@native
+function ImGui_ImplRoblox_RenderDrawData(draw_data)
+    local bd = ImGui_ImplRoblox_GetBackendData()
+    PB("ImGui RenderDrawData")
+
+    PB("ImGui textures")
+    if draw_data.Textures ~= nil then
+        for _, tex in draw_data.Textures:iter() do
+            if tex.Status ~= ImTextureStatus.OK then
+                ImGui_ImplRoblox_UpdateTexture(tex)
+                bd.ForceRedraw = true -- texture contents changed: tiles sampling it must be redrawn
+            end
+        end
+    end
+    PE()
+
+    -- Render rate cap: textures are always updated (imgui expects it), tiles only at bd.RenderRate Hz
+    -- Optional lower cap while scrolling / resizing / moving a window (SetBusyRenderRate, off by default)
+    local rate = bd.RenderRate
+    if bd.BusyRenderRate > 0 then
+        local g = ImGui.GetCurrentContext()
+        local busy = g.WheelingWindow ~= nil or g.MovingWindow ~= nil -- (io.MouseWheel is already cleared by EndFrame)
+        if not busy and g.ActiveId ~= 0 then
+            local w = g.ActiveIdWindow
+            local cur = g.MouseCursor -- ResizeAll..ResizeNWSE while a resize grip/border is held
+            busy = (cur >= ImGuiMouseCursor.ResizeAll and cur <= ImGuiMouseCursor.ResizeNWSE)
+                or (w ~= nil and (g.ActiveId == ImGui.GetWindowScrollbarID(w, ImGuiAxis.X) or g.ActiveId == ImGui.GetWindowScrollbarID(w, ImGuiAxis.Y)))
+        end
+        if busy and (rate <= 0 or bd.BusyRenderRate < rate) then rate = bd.BusyRenderRate end
+    end
+    if rate > 0 then
+        local now = os.clock()
+        if now + 0.002 < bd.NextRender then PE(); return end
+        bd.NextRender = math.max(bd.NextRender + 1 / rate, now)
+    end
+
+    local sw, sh = floor(draw_data.DisplaySize.x), floor(draw_data.DisplaySize.y)
+    if sw <= 0 or sh <= 0 then PE(); return end
+    local ox, oy = draw_data.DisplayPos.x, draw_data.DisplayPos.y
+    local lim_x0, lim_y0, lim_x1, lim_y1 = -CLIP_PAD, -CLIP_PAD, sw + CLIP_PAD, sh + CLIP_PAD
+    bd.FrameNo += 1
+    local frame_no = bd.FrameNo
+    local force = bd.ForceRedraw
+    bd.ForceRedraw = false
+
+    local n = 0
+    local z = 0
+    for _, draw_list in draw_data.CmdLists:iter() do
+        -- Pass 1: collect this list's primitives and their bounds
+        PB("ImGui collect")
+        local first = n + 1
+        local vtx, idx = draw_list.VtxBuffer.Data, draw_list.IdxBuffer.Data
+        local ccx0, ccy0, ccx1, ccy1 = draw_list._ContentClipX0, draw_list._ContentClipY0, draw_list._ContentClipX1, draw_list._ContentClipY1
+        local content_x0, content_y0, content_x1, content_y1
+        if ccx0 then
+            content_x0, content_y0 = max(floor(ccx0 - ox), lim_x0), max(floor(ccy0 - oy), lim_y0)
+            content_x1, content_y1 = min(floor(ccx1 - ox), lim_x1), min(floor(ccy1 - oy), lim_y1)
+        end
+        local seen_content = false
+        for _, pcmd in draw_list.CmdBuffer:iter() do
+            if pcmd.UserCallback ~= nil then
+                pcmd.UserCallback(draw_list, pcmd)
+            elseif pcmd.ElemCount > 0 then
+                local clip = pcmd.ClipRect
+                local cx0, cy0 = max(floor(clip.x - ox), lim_x0), max(floor(clip.y - oy), lim_y0)
+                local cx1, cy1 = min(floor(clip.z - ox), lim_x1), min(floor(clip.w - oy), lim_y1)
+                local kind = 1
+                if ccx0 and clip.x >= ccx0 and clip.y >= ccy0 and clip.z <= ccx1 and clip.w <= ccy1 then
+                    kind = 2; seen_content = true
+                    if clip.x == ccx0 and clip.y == ccy0 and clip.z == ccx1 and clip.w == ccy1 then
+                        -- clipped by the layer's clip frame instead: partly visible rows stay hash-stable while scrolling
+                        cx0, cy0, cx1, cy1 = lim_x0, lim_y0, lim_x1, lim_y1
+                    end
+                elseif seen_content then
+                    kind = 3
+                end
+                if cx1 > cx0 and cy1 > cy0 then
+                    local tex_id = pcmd:GetTexID()
+                    local t = bd.Textures[tex_id]
+                    local vo = pcmd.VtxOffset
+                    local i, last = pcmd.IdxOffset + 1, pcmd.IdxOffset + pcmd.ElemCount
+                    while i <= last do
+                        local ia, ic = idx[i], idx[i + 2]
+                        local va, vb, vc = vtx[vo + ia], vtx[vo + idx[i + 1]], vtx[vo + ic]
+                        local vd = false
+                        local gk = false
+                        local pa, pb, pc = va[1], vb[1], vc[1]
+                        local bx0, by0, bx1, by1
+                        if i + 5 <= last and idx[i + 3] == ia and idx[i + 4] == ic then
+                            local d = vtx[vo + idx[i + 5]]
+                            local pd = d[1]
+                            -- axis aligned quad (TL, TR, BR, BL)
+                            if pa.y == pb.y and pb.x == pc.x and pc.y == pd.y and pd.x == pa.x and pa.x < pb.x and pa.y < pd.y then
+                                local col = va[3]
+                                local ta, tb, tc, td = va[2], vb[2], vc[2], d[2]
+                                if vb[3] == col and vc[3] == col and d[3] == col then
+                                    if tb.x == tc.x and tb.y == ta.y and td.x == ta.x and td.y == tc.y then vd = d end
+                                elseif ta.x == tb.x and ta.x == tc.x and ta.x == td.x and ta.y == tb.y and ta.y == tc.y and ta.y == td.y then
+                                    -- constant uv, linear gradient: vertical (top/bottom pairs equal) or horizontal (left/right pairs equal)
+                                    if vb[3] == col and d[3] == vc[3] then vd = d; gk = 1
+                                    elseif d[3] == col and vb[3] == vc[3] then vd = d; gk = 2 end
+                                end
+                                if vd then
+                                    bx0, by0 = ceil(pa.x - ox - 0.5), ceil(pa.y - oy - 0.5)
+                                    bx1, by1 = ceil(pc.x - ox - 0.5), ceil(pc.y - oy - 0.5)
+                                end
+                            end
+                        end
+                        if vd then
+                            i = i + 6
+                        else
+                            bx0, by0 = floor(min(pa.x, pb.x, pc.x) - ox), floor(min(pa.y, pb.y, pc.y) - oy)
+                            bx1, by1 = ceil(max(pa.x, pb.x, pc.x) - ox) + 1, ceil(max(pa.y, pb.y, pc.y) - oy) + 1
+                            i = i + 3
+                        end
+                        if bx0 < cx0 then bx0 = cx0 end
+                        if by0 < cy0 then by0 = cy0 end
+                        if bx1 > cx1 then bx1 = cx1 end
+                        if by1 > cy1 then by1 = cy1 end
+                        if bx0 < bx1 and by0 < by1 then
+                            n = n + 1
+                            pr_a[n], pr_b[n], pr_c[n], pr_d[n], pr_t[n], pr_g[n], pr_tex[n] = va, vb, vc, vd, t, gk, tex_id
+                            pr_cx0[n], pr_cy0[n], pr_cx1[n], pr_cy1[n] = cx0, cy0, cx1, cy1
+                            pr_bx0[n], pr_by0[n], pr_bx1[n], pr_by1[n] = bx0, by0, bx1, by1
+                            pr_k[n] = kind
+                        end
+                    end
+                end
+            end
+        end
+        PE()
+
+        -- Split into layer kinds and place each one
+        local set = bd.Layers[draw_list]
+        local nk1, nk2, nk3 = 0, 0, 0
+        local o1x, o1y, o3x, o3y = math.huge, math.huge, math.huge, math.huge
+        for p = first, n do
+            local k = pr_k[p]
+            if k == 1 then
+                nk1 += 1; plist1[nk1] = p
+                if pr_bx0[p] < o1x then o1x = pr_bx0[p] end
+                if pr_by0[p] < o1y then o1y = pr_by0[p] end
+            elseif k == 2 then
+                nk2 += 1; plist2[nk2] = p
+            else
+                nk3 += 1; plist3[nk3] = p
+                if pr_bx0[p] < o3x then o3x = pr_bx0[p] end
+                if pr_by0[p] < o3y then o3y = pr_by0[p] end
+            end
+        end
+        if nk1 > 0 then
+            z += 1
+            DrawLayer(bd, GetLayer(bd, draw_list, 1), plist1, nk1, o1x, o1y, ox, oy, force, z)
+        elseif set and set[1] then HideLayer(set[1]) end
+        if nk2 > 0 then
+            z += 1
+            DrawLayer(bd, GetLayer(bd, draw_list, 2), plist2, nk2, floor(draw_list._ScrollOriginX - ox), floor(draw_list._ScrollOriginY - oy), ox, oy, force, z,
+                content_x0, content_y0, content_x1, content_y1)
+        elseif set and set[2] then HideLayer(set[2]) end
+        if nk3 > 0 then
+            z += 1
+            DrawLayer(bd, GetLayer(bd, draw_list, 3), plist3, nk3, o3x, o3y, ox, oy, force, z)
+        elseif set and set[3] then HideLayer(set[3]) end
+        set = bd.Layers[draw_list]
+        if set then set.LastUsed = frame_no end
     end
 
     -- Hide layers not drawn this frame; free long unused ones (closed windows, old tooltips)
-    for draw_list, layer in pairs(bd.Layers) do
+    for draw_list, set in pairs(bd.Layers) do
-        if layer.LastUsed ~= frame_no then
+        if set.LastUsed ~= frame_no then
-            if layer.Visible then layer.Visible = false; layer.Frame.Visible = false end
+            for kind = 1, 3 do if set[kind] then HideLayer(set[kind]) end end
-            if frame_no - layer.LastUsed > LAYER_KEEP_FRAMES then
+            if frame_no - set.LastUsed > LAYER_KEEP_FRAMES then
-                DestroyLayer(layer)
+                DestroyLayerSet(set)
                 bd.Layers[draw_list] = nil
             end
         end
@@ -34093,7 +34184,7 @@ function ImGui_ImplRoblox_NewFrame()
     local want = io.WantCaptureMouse
     if want ~= bd.TilesActive then
         bd.TilesActive = want
-        for _, layer in pairs(bd.Layers) do for _, tile in pairs(layer.Tiles) do tile.Label.Active = want end end
+        for _, set in pairs(bd.Layers) do for kind = 1, 3 do local layer = set[kind]; if layer then for _, tile in pairs(layer.Tiles) do tile.Label.Active = want end end end end
     end
     PE()
 end

imgui/backend/imgui_impl_roblox.lua

@@ -421,7 +421,7 @@ end
 -- relative to the layer's origin (top-left of its content). Primitives are hashed into tiles in layer-relative
 -- coordinates, so moving a window only moves its Frame: no tile changes, nothing re-rasterized or uploaded.
 -- Only tiles whose hash changed are redrawn; the hash covers everything that affects a tile's pixels.
-local TILE = 256
+local TILE = 128
 TILE_SIZE = Vector2.new(TILE, TILE)
 local P1, P2 = 2147483647, 2147483629 -- two independent 31 bit hashes per tile (collision odds ~2^-62)
 local KEY_W = 64 -- tile key = ty * KEY_W + tx (layers up to 16384 px wide)
@@ -433,6 +433,8 @@ local pr_a, pr_b, pr_c, pr_d, pr_t, pr_g = {}, {}, {}, {}, {}, {} -- vertices (p
 local pr_cx0, pr_cy0, pr_cx1, pr_cy1 = {}, {}, {}, {}  -- clip (screen pixels)
 local pr_bx0, pr_by0, pr_bx1, pr_by1 = {}, {}, {}, {}  -- clipped bounds (screen pixels)
 local pr_tex = {}                                      -- texture id
+local pr_k = {}                                        -- layer kind (1..3)
+local plist1, plist2, plist3 = {}, {}, {}              -- primitive indices per layer kind
 
 @native
 local function HashVertex(h1, h2, v, ox, oy)
@@ -495,22 +497,43 @@ local function DrawRectGradient(x0, y0, x1, y1, ca, cb, kind, t, u, v, cx0, cy0,
     end
 end
 
-local function GetLayer(bd, draw_list)
+-- Layer kinds per draw list: 1 = drawn before the window content (background, title bar, borders, scrollbar),
-    local layer = bd.Layers[draw_list]
+-- 2 = window content (positioned at the scroll origin inside a ClipsDescendants frame, so scrolling just moves it),
-    if layer then return layer end
+-- 3 = anything not clipped to the content drawn after content started (menu bar, overlays). Stacked 1 < 2 < 3.
+local function NewFrame(parent, clips)
     local frame = Instance.new("Frame")
     frame.Name = "Layer"
     frame.BackgroundTransparency = 1
     frame.BorderSizePixel = 0
     frame.Size = UDim2.fromOffset(0, 0)
+    frame.ClipsDescendants = clips
     frame.Visible = false
-    frame.Parent = bd.Gui
+    frame.Parent = parent
-    layer = { Frame = frame, Tiles = {}, TH1 = {}, TH2 = {}, TN = {}, TL = {}, Touched = {}, NTouched = 0,
+    return frame
-              Visible = false, X = false, Y = false, Z = -1, LastUsed = 0 }
+end
-    bd.Layers[draw_list] = layer
+
+local function GetLayer(bd, draw_list, kind)
+    local set = bd.Layers[draw_list]
+    if not set then set = { LastUsed = 0 }; bd.Layers[draw_list] = set end
+    local layer = set[kind]
+    if layer then return layer end
+    local root, frame
+    if kind == 2 then
+        root = NewFrame(bd.Gui, true)
+        frame = NewFrame(root, false); frame.Visible = true
+    else
+        frame = NewFrame(bd.Gui, false); root = frame
+    end
+    layer = { Root = root, Frame = frame, Tiles = {}, TH1 = {}, TH2 = {}, TN = {}, TL = {}, TX = {}, TY = {}, Touched = {}, NTouched = 0,
+              Visible = false, X = false, Y = false, Z = -1, CX0 = false, CY0 = false, CX1 = false, CY1 = false }
+    set[kind] = layer
     return layer
 end
 
+local function HideLayer(layer)
+    if layer.Visible then layer.Visible = false; layer.Root.Visible = false end
+end
+
 local function GetTile(bd, layer, key, tx, ty)
     local tile = layer.Tiles[key]
     if tile then return tile end
@@ -533,13 +556,18 @@ local function GetTile(bd, layer, key, tx, ty)
     return tile
 end
 
-local function DestroyLayer(layer)
+local function DestroyLayerSet(set)
+    for kind = 1, 3 do
+        local layer = set[kind]
+        if layer then
             for _, tile in pairs(layer.Tiles) do tile.Image:Destroy() end
-    layer.Frame:Destroy()
+            layer.Root:Destroy()
+        end
+    end
 end
 
 local function DestroyTiles(bd)
-    for _, layer in pairs(bd.Layers) do DestroyLayer(layer) end
+    for _, set in pairs(bd.Layers) do DestroyLayerSet(set) end
     bd.Layers = {}
 end
 
@@ -550,134 +578,15 @@ local function PB(name) if profiling then profilebegin(name) end end
 local function PE() if profiling then profileend() end end
 
 @native
-function ImGui_ImplRoblox_RenderDrawData(draw_data)
+local function DrawLayer(bd, layer, plist, np, lx0, ly0, ox, oy, force, z, clip_x0, clip_y0, clip_x1, clip_y1)
-    local bd = ImGui_ImplRoblox_GetBackendData()
-    PB("ImGui RenderDrawData")
-
-    PB("ImGui textures")
-    if draw_data.Textures ~= nil then
-        for _, tex in draw_data.Textures:iter() do
-            if tex.Status ~= ImTextureStatus.OK then
-                ImGui_ImplRoblox_UpdateTexture(tex)
-                bd.ForceRedraw = true -- texture contents changed: tiles sampling it must be redrawn
-            end
-        end
-    end
-    PE()
-
-    -- Render rate cap: textures are always updated (imgui expects it), tiles only at bd.RenderRate Hz
-    -- Optional lower cap while scrolling / resizing / moving a window (SetBusyRenderRate, off by default)
-    local rate = bd.RenderRate
-    if bd.BusyRenderRate > 0 then
-        local g = ImGui.GetCurrentContext()
-        local busy = g.WheelingWindow ~= nil or g.MovingWindow ~= nil -- (io.MouseWheel is already cleared by EndFrame)
-        if not busy and g.ActiveId ~= 0 then
-            local w = g.ActiveIdWindow
-            local cur = g.MouseCursor -- ResizeAll..ResizeNWSE while a resize grip/border is held
-            busy = (cur >= ImGuiMouseCursor.ResizeAll and cur <= ImGuiMouseCursor.ResizeNWSE)
-                or (w ~= nil and (g.ActiveId == ImGui.GetWindowScrollbarID(w, ImGuiAxis.X) or g.ActiveId == ImGui.GetWindowScrollbarID(w, ImGuiAxis.Y)))
-        end
-        if busy and (rate <= 0 or bd.BusyRenderRate < rate) then rate = bd.BusyRenderRate end
-    end
-    if rate > 0 then
-        local now = os.clock()
-        if now + 0.002 < bd.NextRender then PE(); return end
-        bd.NextRender = math.max(bd.NextRender + 1 / rate, now)
-    end
-
-    local sw, sh = floor(draw_data.DisplaySize.x), floor(draw_data.DisplaySize.y)
-    if sw <= 0 or sh <= 0 then PE(); return end
-    local ox, oy = draw_data.DisplayPos.x, draw_data.DisplayPos.y
-    local lim_x0, lim_y0, lim_x1, lim_y1 = -CLIP_PAD, -CLIP_PAD, sw + CLIP_PAD, sh + CLIP_PAD
-    bd.FrameNo += 1
-    local frame_no = bd.FrameNo
-    local force = bd.ForceRedraw
-    bd.ForceRedraw = false
     local scale = bd.Scale
-
-    local n = 0
-    local z = 0
-    for _, draw_list in draw_data.CmdLists:iter() do
-        -- Pass 1: collect this list's primitives and their bounds
-        PB("ImGui collect")
-        local first = n + 1
-        local lx0, ly0 = math.huge, math.huge
-        local vtx, idx = draw_list.VtxBuffer.Data, draw_list.IdxBuffer.Data
-        for _, pcmd in draw_list.CmdBuffer:iter() do
-            if pcmd.UserCallback ~= nil then
-                pcmd.UserCallback(draw_list, pcmd)
-            elseif pcmd.ElemCount > 0 then
-                local clip = pcmd.ClipRect
-                local cx0, cy0 = max(floor(clip.x - ox), lim_x0), max(floor(clip.y - oy), lim_y0)
-                local cx1, cy1 = min(floor(clip.z - ox), lim_x1), min(floor(clip.w - oy), lim_y1)
-                if cx1 > cx0 and cy1 > cy0 then
-                    local tex_id = pcmd:GetTexID()
-                    local t = bd.Textures[tex_id]
-                    local vo = pcmd.VtxOffset
-                    local i, last = pcmd.IdxOffset + 1, pcmd.IdxOffset + pcmd.ElemCount
-                    while i <= last do
-                        local ia, ic = idx[i], idx[i + 2]
-                        local va, vb, vc = vtx[vo + ia], vtx[vo + idx[i + 1]], vtx[vo + ic]
-                        local vd = false
-                        local gk = false
-                        local pa, pb, pc = va[1], vb[1], vc[1]
-                        local bx0, by0, bx1, by1
-                        if i + 5 <= last and idx[i + 3] == ia and idx[i + 4] == ic then
-                            local d = vtx[vo + idx[i + 5]]
-                            local pd = d[1]
-                            -- axis aligned quad (TL, TR, BR, BL)
-                            if pa.y == pb.y and pb.x == pc.x and pc.y == pd.y and pd.x == pa.x and pa.x < pb.x and pa.y < pd.y then
-                                local col = va[3]
-                                local ta, tb, tc, td = va[2], vb[2], vc[2], d[2]
-                                if vb[3] == col and vc[3] == col and d[3] == col then
-                                    if tb.x == tc.x and tb.y == ta.y and td.x == ta.x and td.y == tc.y then vd = d end
-                                elseif ta.x == tb.x and ta.x == tc.x and ta.x == td.x and ta.y == tb.y and ta.y == tc.y and ta.y == td.y then
-                                    -- constant uv, linear gradient: vertical (top/bottom pairs equal) or horizontal (left/right pairs equal)
-                                    if vb[3] == col and d[3] == vc[3] then vd = d; gk = 1
-                                    elseif d[3] == col and vb[3] == vc[3] then vd = d; gk = 2 end
-                                end
-                                if vd then
-                                    bx0, by0 = ceil(pa.x - ox - 0.5), ceil(pa.y - oy - 0.5)
-                                    bx1, by1 = ceil(pc.x - ox - 0.5), ceil(pc.y - oy - 0.5)
-                                end
-                            end
-                        end
-                        if vd then
-                            i = i + 6
-                        else
-                            bx0, by0 = floor(min(pa.x, pb.x, pc.x) - ox), floor(min(pa.y, pb.y, pc.y) - oy)
-                            bx1, by1 = ceil(max(pa.x, pb.x, pc.x) - ox) + 1, ceil(max(pa.y, pb.y, pc.y) - oy) + 1
-                            i = i + 3
-                        end
-                        if bx0 < cx0 then bx0 = cx0 end
-                        if by0 < cy0 then by0 = cy0 end
-                        if bx1 > cx1 then bx1 = cx1 end
-                        if by1 > cy1 then by1 = cy1 end
-                        if bx0 < bx1 and by0 < by1 then
-                            n = n + 1
-                            pr_a[n], pr_b[n], pr_c[n], pr_d[n], pr_t[n], pr_g[n], pr_tex[n] = va, vb, vc, vd, t, gk, tex_id
-                            pr_cx0[n], pr_cy0[n], pr_cx1[n], pr_cy1[n] = cx0, cy0, cx1, cy1
-                            pr_bx0[n], pr_by0[n], pr_bx1[n], pr_by1[n] = bx0, by0, bx1, by1
-                            if bx0 < lx0 then lx0 = bx0 end
-                            if by0 < ly0 then ly0 = by0 end
-                        end
-                    end
-                end
-            end
-        end
-        PE()
-
-        local layer = GetLayer(bd, draw_list)
-        layer.LastUsed = frame_no
-        if n < first then
-            if layer.Visible then layer.Visible = false; layer.Frame.Visible = false end
-        else
     -- Pass 2: hash primitives into layer-relative tiles
     PB("ImGui tile hash")
     local th1, th2, tn, tl, touched = layer.TH1, layer.TH2, layer.TN, layer.TL, layer.Touched
     for k = 1, layer.NTouched do tn[touched[k]] = 0 end
     local nt = 0
-            for p = first, n do
+    for pi = 1, np do
+        local p = plist[pi]
         local tex_id = pr_tex[p]
         -- The clip rect only affects pixels inside the primitive's bounds, so hash the clipped bounds (relative)
         -- instead of the clip itself: a window clipped by the (fixed) viewport rect stays hash-stable when moved.
@@ -700,6 +609,7 @@ function ImGui_ImplRoblox_RenderDrawData(draw_data)
                     if not tl[key] then tl[key] = {} end
                     nt = nt + 1
                     touched[nt] = key
+                    layer.TX[key], layer.TY[key] = tx, ty
                 end
                 k = k + 1
                 tn[key] = k
@@ -713,14 +623,25 @@ function ImGui_ImplRoblox_RenderDrawData(draw_data)
     PE()
 
     -- Place the layer (this is all a window move costs)
-            local frame = layer.Frame
+    local root = layer.Root
+    if root ~= layer.Frame then
+        -- content: clip frame at the content clip rect, tiles frame at the scroll origin relative to it
+        if layer.CX0 ~= clip_x0 or layer.CY0 ~= clip_y0 or layer.CX1 ~= clip_x1 or layer.CY1 ~= clip_y1 then
+            layer.CX0, layer.CY0, layer.CX1, layer.CY1 = clip_x0, clip_y0, clip_x1, clip_y1
+            root.Position = UDim2.fromOffset(clip_x0 / scale, clip_y0 / scale)
+            root.Size = UDim2.fromOffset((clip_x1 - clip_x0) / scale, (clip_y1 - clip_y0) / scale)
+            layer.X = false
+        end
         if layer.X ~= lx0 or layer.Y ~= ly0 then
             layer.X, layer.Y = lx0, ly0
-                frame.Position = UDim2.fromOffset(lx0 / scale, ly0 / scale)
+            layer.Frame.Position = UDim2.fromOffset((lx0 - clip_x0) / scale, (ly0 - clip_y0) / scale)
         end
-            z = z + 1
+    elseif layer.X ~= lx0 or layer.Y ~= ly0 then
-            if layer.Z ~= z then layer.Z = z; frame.ZIndex = z end
+        layer.X, layer.Y = lx0, ly0
-            if not layer.Visible then layer.Visible = true; frame.Visible = true end
+        root.Position = UDim2.fromOffset(lx0 / scale, ly0 / scale)
+    end
+    if layer.Z ~= z then layer.Z = z; root.ZIndex = z end
+    if not layer.Visible then layer.Visible = true; root.Visible = true end
 
     -- Pass 3: redraw + upload changed tiles, hide unused ones
     PB("ImGui raster+upload")
@@ -732,8 +653,7 @@ function ImGui_ImplRoblox_RenderDrawData(draw_data)
     for kk = 1, nt do
         local key = touched[kk]
         local count = tn[key]
-                local tx, ty = key % KEY_W, floor(key / KEY_W)
+        local tx, ty = layer.TX[key], layer.TY[key]
-                if tx < 0 then tx = tx + KEY_W; ty = ty - 1 end
         local tile = GetTile(bd, layer, key, tx, ty)
         if force or tile.H1 ~= th1[key] or tile.H2 ~= th2[key] then
             tile.H1, tile.H2 = th1[key], th2[key]
@@ -800,14 +720,180 @@ function ImGui_ImplRoblox_RenderDrawData(draw_data)
     end
     PE()
 end
+
+@native
+function ImGui_ImplRoblox_RenderDrawData(draw_data)
+    local bd = ImGui_ImplRoblox_GetBackendData()
+    PB("ImGui RenderDrawData")
+
+    PB("ImGui textures")
+    if draw_data.Textures ~= nil then
+        for _, tex in draw_data.Textures:iter() do
+            if tex.Status ~= ImTextureStatus.OK then
+                ImGui_ImplRoblox_UpdateTexture(tex)
+                bd.ForceRedraw = true -- texture contents changed: tiles sampling it must be redrawn
+            end
+        end
+    end
+    PE()
+
+    -- Render rate cap: textures are always updated (imgui expects it), tiles only at bd.RenderRate Hz
+    -- Optional lower cap while scrolling / resizing / moving a window (SetBusyRenderRate, off by default)
+    local rate = bd.RenderRate
+    if bd.BusyRenderRate > 0 then
+        local g = ImGui.GetCurrentContext()
+        local busy = g.WheelingWindow ~= nil or g.MovingWindow ~= nil -- (io.MouseWheel is already cleared by EndFrame)
+        if not busy and g.ActiveId ~= 0 then
+            local w = g.ActiveIdWindow
+            local cur = g.MouseCursor -- ResizeAll..ResizeNWSE while a resize grip/border is held
+            busy = (cur >= ImGuiMouseCursor.ResizeAll and cur <= ImGuiMouseCursor.ResizeNWSE)
+                or (w ~= nil and (g.ActiveId == ImGui.GetWindowScrollbarID(w, ImGuiAxis.X) or g.ActiveId == ImGui.GetWindowScrollbarID(w, ImGuiAxis.Y)))
+        end
+        if busy and (rate <= 0 or bd.BusyRenderRate < rate) then rate = bd.BusyRenderRate end
+    end
+    if rate > 0 then
+        local now = os.clock()
+        if now + 0.002 < bd.NextRender then PE(); return end
+        bd.NextRender = math.max(bd.NextRender + 1 / rate, now)
+    end
+
+    local sw, sh = floor(draw_data.DisplaySize.x), floor(draw_data.DisplaySize.y)
+    if sw <= 0 or sh <= 0 then PE(); return end
+    local ox, oy = draw_data.DisplayPos.x, draw_data.DisplayPos.y
+    local lim_x0, lim_y0, lim_x1, lim_y1 = -CLIP_PAD, -CLIP_PAD, sw + CLIP_PAD, sh + CLIP_PAD
+    bd.FrameNo += 1
+    local frame_no = bd.FrameNo
+    local force = bd.ForceRedraw
+    bd.ForceRedraw = false
+
+    local n = 0
+    local z = 0
+    for _, draw_list in draw_data.CmdLists:iter() do
+        -- Pass 1: collect this list's primitives and their bounds
+        PB("ImGui collect")
+        local first = n + 1
+        local vtx, idx = draw_list.VtxBuffer.Data, draw_list.IdxBuffer.Data
+        local ccx0, ccy0, ccx1, ccy1 = draw_list._ContentClipX0, draw_list._ContentClipY0, draw_list._ContentClipX1, draw_list._ContentClipY1
+        local content_x0, content_y0, content_x1, content_y1
+        if ccx0 then
+            content_x0, content_y0 = max(floor(ccx0 - ox), lim_x0), max(floor(ccy0 - oy), lim_y0)
+            content_x1, content_y1 = min(floor(ccx1 - ox), lim_x1), min(floor(ccy1 - oy), lim_y1)
+        end
+        local seen_content = false
+        for _, pcmd in draw_list.CmdBuffer:iter() do
+            if pcmd.UserCallback ~= nil then
+                pcmd.UserCallback(draw_list, pcmd)
+            elseif pcmd.ElemCount > 0 then
+                local clip = pcmd.ClipRect
+                local cx0, cy0 = max(floor(clip.x - ox), lim_x0), max(floor(clip.y - oy), lim_y0)
+                local cx1, cy1 = min(floor(clip.z - ox), lim_x1), min(floor(clip.w - oy), lim_y1)
+                local kind = 1
+                if ccx0 and clip.x >= ccx0 and clip.y >= ccy0 and clip.z <= ccx1 and clip.w <= ccy1 then
+                    kind = 2; seen_content = true
+                    if clip.x == ccx0 and clip.y == ccy0 and clip.z == ccx1 and clip.w == ccy1 then
+                        -- clipped by the layer's clip frame instead: partly visible rows stay hash-stable while scrolling
+                        cx0, cy0, cx1, cy1 = lim_x0, lim_y0, lim_x1, lim_y1
+                    end
+                elseif seen_content then
+                    kind = 3
+                end
+                if cx1 > cx0 and cy1 > cy0 then
+                    local tex_id = pcmd:GetTexID()
+                    local t = bd.Textures[tex_id]
+                    local vo = pcmd.VtxOffset
+                    local i, last = pcmd.IdxOffset + 1, pcmd.IdxOffset + pcmd.ElemCount
+                    while i <= last do
+                        local ia, ic = idx[i], idx[i + 2]
+                        local va, vb, vc = vtx[vo + ia], vtx[vo + idx[i + 1]], vtx[vo + ic]
+                        local vd = false
+                        local gk = false
+                        local pa, pb, pc = va[1], vb[1], vc[1]
+                        local bx0, by0, bx1, by1
+                        if i + 5 <= last and idx[i + 3] == ia and idx[i + 4] == ic then
+                            local d = vtx[vo + idx[i + 5]]
+                            local pd = d[1]
+                            -- axis aligned quad (TL, TR, BR, BL)
+                            if pa.y == pb.y and pb.x == pc.x and pc.y == pd.y and pd.x == pa.x and pa.x < pb.x and pa.y < pd.y then
+                                local col = va[3]
+                                local ta, tb, tc, td = va[2], vb[2], vc[2], d[2]
+                                if vb[3] == col and vc[3] == col and d[3] == col then
+                                    if tb.x == tc.x and tb.y == ta.y and td.x == ta.x and td.y == tc.y then vd = d end
+                                elseif ta.x == tb.x and ta.x == tc.x and ta.x == td.x and ta.y == tb.y and ta.y == tc.y and ta.y == td.y then
+                                    -- constant uv, linear gradient: vertical (top/bottom pairs equal) or horizontal (left/right pairs equal)
+                                    if vb[3] == col and d[3] == vc[3] then vd = d; gk = 1
+                                    elseif d[3] == col and vb[3] == vc[3] then vd = d; gk = 2 end
+                                end
+                                if vd then
+                                    bx0, by0 = ceil(pa.x - ox - 0.5), ceil(pa.y - oy - 0.5)
+                                    bx1, by1 = ceil(pc.x - ox - 0.5), ceil(pc.y - oy - 0.5)
+                                end
+                            end
+                        end
+                        if vd then
+                            i = i + 6
+                        else
+                            bx0, by0 = floor(min(pa.x, pb.x, pc.x) - ox), floor(min(pa.y, pb.y, pc.y) - oy)
+                            bx1, by1 = ceil(max(pa.x, pb.x, pc.x) - ox) + 1, ceil(max(pa.y, pb.y, pc.y) - oy) + 1
+                            i = i + 3
+                        end
+                        if bx0 < cx0 then bx0 = cx0 end
+                        if by0 < cy0 then by0 = cy0 end
+                        if bx1 > cx1 then bx1 = cx1 end
+                        if by1 > cy1 then by1 = cy1 end
+                        if bx0 < bx1 and by0 < by1 then
+                            n = n + 1
+                            pr_a[n], pr_b[n], pr_c[n], pr_d[n], pr_t[n], pr_g[n], pr_tex[n] = va, vb, vc, vd, t, gk, tex_id
+                            pr_cx0[n], pr_cy0[n], pr_cx1[n], pr_cy1[n] = cx0, cy0, cx1, cy1
+                            pr_bx0[n], pr_by0[n], pr_bx1[n], pr_by1[n] = bx0, by0, bx1, by1
+                            pr_k[n] = kind
+                        end
+                    end
+                end
+            end
+        end
+        PE()
+
+        -- Split into layer kinds and place each one
+        local set = bd.Layers[draw_list]
+        local nk1, nk2, nk3 = 0, 0, 0
+        local o1x, o1y, o3x, o3y = math.huge, math.huge, math.huge, math.huge
+        for p = first, n do
+            local k = pr_k[p]
+            if k == 1 then
+                nk1 += 1; plist1[nk1] = p
+                if pr_bx0[p] < o1x then o1x = pr_bx0[p] end
+                if pr_by0[p] < o1y then o1y = pr_by0[p] end
+            elseif k == 2 then
+                nk2 += 1; plist2[nk2] = p
+            else
+                nk3 += 1; plist3[nk3] = p
+                if pr_bx0[p] < o3x then o3x = pr_bx0[p] end
+                if pr_by0[p] < o3y then o3y = pr_by0[p] end
+            end
+        end
+        if nk1 > 0 then
+            z += 1
+            DrawLayer(bd, GetLayer(bd, draw_list, 1), plist1, nk1, o1x, o1y, ox, oy, force, z)
+        elseif set and set[1] then HideLayer(set[1]) end
+        if nk2 > 0 then
+            z += 1
+            DrawLayer(bd, GetLayer(bd, draw_list, 2), plist2, nk2, floor(draw_list._ScrollOriginX - ox), floor(draw_list._ScrollOriginY - oy), ox, oy, force, z,
+                content_x0, content_y0, content_x1, content_y1)
+        elseif set and set[2] then HideLayer(set[2]) end
+        if nk3 > 0 then
+            z += 1
+            DrawLayer(bd, GetLayer(bd, draw_list, 3), plist3, nk3, o3x, o3y, ox, oy, force, z)
+        elseif set and set[3] then HideLayer(set[3]) end
+        set = bd.Layers[draw_list]
+        if set then set.LastUsed = frame_no end
     end
 
     -- Hide layers not drawn this frame; free long unused ones (closed windows, old tooltips)
-    for draw_list, layer in pairs(bd.Layers) do
+    for draw_list, set in pairs(bd.Layers) do
-        if layer.LastUsed ~= frame_no then
+        if set.LastUsed ~= frame_no then
-            if layer.Visible then layer.Visible = false; layer.Frame.Visible = false end
+            for kind = 1, 3 do if set[kind] then HideLayer(set[kind]) end end
-            if frame_no - layer.LastUsed > LAYER_KEEP_FRAMES then
+            if frame_no - set.LastUsed > LAYER_KEEP_FRAMES then
-                DestroyLayer(layer)
+                DestroyLayerSet(set)
                 bd.Layers[draw_list] = nil
             end
         end
@@ -941,7 +1027,7 @@ function ImGui_ImplRoblox_NewFrame()
     local want = io.WantCaptureMouse
     if want ~= bd.TilesActive then
         bd.TilesActive = want
-        for _, layer in pairs(bd.Layers) do for _, tile in pairs(layer.Tiles) do tile.Label.Active = want end end
+        for _, set in pairs(bd.Layers) do for kind = 1, 3 do local layer = set[kind]; if layer then for _, tile in pairs(layer.Tiles) do tile.Label.Active = want end end end end
     end
     PE()
 end

imgui/imgui.lua

@@ -7150,6 +7150,10 @@ function ImGui.Begin(name, open, flags)
 
     if bit32.band(flags, ImGuiWindowFlags.DockNodeHost) == 0 and not window.SkipRefresh then
         ImGui.PushClipRect(window.InnerClipRect.Min, window.InnerClipRect.Max, true)
+        -- [Roblox backend] content clip + scroll origin: lets the backend move scrolled content instead of redrawing it
+        local dl, cr = window.DrawList, window.DrawList._CmdHeader.ClipRect
+        dl._ContentClipX0, dl._ContentClipY0, dl._ContentClipX1, dl._ContentClipY1 = cr.x, cr.y, cr.z, cr.w
+        dl._ScrollOriginX, dl._ScrollOriginY = window.Pos.x - window.Scroll.x, window.Pos.y - window.Scroll.y
     end
 
     window.WriteAccessed = false

imgui/imgui_draw.lua

@@ -3158,6 +3158,7 @@ end
 
 -- TODO:
 function MT.ImDrawList:_ResetForNewFrame()
+    self._ContentClipX0 = nil -- set again by Begin() (Roblox backend scroll reuse)
     if self._Splitter._Count > 1 then
         self._Splitter:Merge(self)
     end

tools/test/scripts/t_composite.luau

@@ -13,21 +13,26 @@ local frame = 0
 
 local function composite(gui)
     local screen = buffer.create(W * H * 3)
-    local function walk(inst, ox, oy)
+    local function walk(inst, ox, oy, kx0, ky0, kx1, ky1)
         local kids = inst:GetChildren()
         table.sort(kids, function(a, b) return (a.ZIndex or 1) < (b.ZIndex or 1) end) -- table.sort isn't stable, but siblings with equal ZIndex never overlap here
         for _, c in ipairs(kids) do
             if c.Visible ~= false then
                 local x, y = ox + (c.Position and c.Position.X or 0), oy + (c.Position and c.Position.Y or 0)
+                local cx0, cy0, cx1, cy1 = kx0, ky0, kx1, ky1
+                if c.ClipsDescendants then
+                    cx0, cy0 = math.max(cx0, x), math.max(cy0, y)
+                    cx1, cy1 = math.min(cx1, x + c.Size.X), math.min(cy1, y + c.Size.Y)
+                end
                 if c.ClassName == "ImageLabel" then
                     local img = c.ImageContent.Object
                     local px, sz = img.Pixels, img.Size.X
                     for ty = 0, sz - 1 do
                         local sy = y + ty
-                        if sy >= 0 and sy < H then
+                        if sy >= ky0 and sy < ky1 then
                             for tx = 0, sz - 1 do
                                 local sx = x + tx
-                                if sx >= 0 and sx < W then
+                                if sx >= kx0 and sx < kx1 then
                                     local o = (ty * sz + tx) * 4
                                     local a = buffer.readu8(px, o + 3)
                                     if a > 0 then
@@ -43,11 +48,11 @@ local function composite(gui)
                         end
                     end
                 end
-                walk(c, x, y)
+                walk(c, x, y, cx0, cy0, cx1, cy1)
             end
         end
     end
-    walk(gui, 0, 0)
+    walk(gui, 0, 0, 0, 0, W, H)
     return screen
 end