Tables: clarify assumption that rendering of bg/borders in bg0/bg1 are cpu-clipped allowing frozen/unfrozen to share drawcmd + remove offset on outer borders of scrolling tables.

Author: ocornut

imgui_internal.h

@@ -2019,7 +2019,8 @@ struct ImGuiTable
     ImRect                      WorkRect;
     ImRect                      InnerClipRect;
     ImRect                      BgClipRect;                 // We use this to cpu-clip cell background color fill
-    ImRect                      BgClipRectForDrawCmd;
+    ImRect                      Bg0ClipRectForDrawCmd;      // Actual ImDrawCmd clip rect for BG0/1 channel. This tends to be == OuterWindow->ClipRect at BeginTable() because output in BG0/BG1 is cpu-clipped
+    ImRect                      Bg2ClipRectForDrawCmd;      // Actual ImDrawCmd clip rect for BG2 channel. This tends to be a correct, tight-fit, because output to BG2 are done by widgets relying on regular ClipRect.
     ImRect                      HostClipRect;               // This is used to check if we can eventually merge our columns draw calls into the current draw call of the current window.
     ImRect                      HostBackupWorkRect;         // Backup of InnerWindow->WorkRect at the end of BeginTable()
     ImRect                      HostBackupParentWorkRect;   // Backup of InnerWindow->ParentWorkRect at the end of BeginTable()

imgui_tables.cpp

@@ -1601,7 +1601,7 @@ void ImGui::TableEndRow(ImGuiTable* table)
             // In theory we could call SetWindowClipRectBeforeSetChannel() but since we know TableEndRow() is
             // always followed by a change of clipping rectangle we perform the smallest overwrite possible here.
             if ((table->Flags & ImGuiTableFlags_NoClip) == 0)
-                window->DrawList->_CmdHeader.ClipRect = table->BgClipRectForDrawCmd.ToVec4();
+                window->DrawList->_CmdHeader.ClipRect = table->Bg0ClipRectForDrawCmd.ToVec4();
             table->DrawSplitter.SetCurrentChannel(window->DrawList, TABLE_DRAW_CHANNEL_BG0);
         }
 
@@ -1657,10 +1657,10 @@ void ImGui::TableEndRow(ImGuiTable* table)
 
         // BgClipRect starts as table->InnerClipRect, reduce it now and make BgClipRectForDrawCmd == BgClipRect
         float y0 = ImMax(table->RowPosY2 + 1, window->InnerClipRect.Min.y);
-        table->BgClipRect.Min.y = table->BgClipRectForDrawCmd.Min.y = ImMin(y0, window->InnerClipRect.Max.y);
-        table->BgClipRect.Max.y = table->BgClipRectForDrawCmd.Max.y = window->InnerClipRect.Max.y;
+        table->BgClipRect.Min.y = table->Bg2ClipRectForDrawCmd.Min.y = ImMin(y0, window->InnerClipRect.Max.y);
+        table->BgClipRect.Max.y = table->Bg2ClipRectForDrawCmd.Max.y = window->InnerClipRect.Max.y;
         table->Bg2DrawChannelCurrent = table->Bg2DrawChannelUnfrozen;
-        IM_ASSERT(table->BgClipRectForDrawCmd.Min.y <= table->BgClipRectForDrawCmd.Max.y);
+        IM_ASSERT(table->Bg2ClipRectForDrawCmd.Min.y <= table->Bg2ClipRectForDrawCmd.Max.y);
 
         float row_height = table->RowPosY2 - table->RowPosY1;
         table->RowPosY2 = window->DC.CursorPos.y = table->WorkRect.Min.y + table->RowPosY2 - table->OuterRect.Min.y;
@@ -1669,7 +1669,7 @@ void ImGui::TableEndRow(ImGuiTable* table)
         {
             ImGuiTableColumn* column = &table->Columns[column_n];
             column->DrawChannelCurrent = column->DrawChannelUnfrozen;
-            column->ClipRect.Min.y = table->BgClipRectForDrawCmd.Min.y;
+            column->ClipRect.Min.y = table->Bg2ClipRectForDrawCmd.Min.y;
         }
 
         // Update cliprect ahead of TableBeginCell() so clipper can access to new ClipRect->Min.y
@@ -2019,7 +2019,7 @@ void ImGui::TablePushBackgroundChannel()
 
     // Optimization: avoid SetCurrentChannel() + PushClipRect()
     table->HostBackupInnerClipRect = window->ClipRect;
-    SetWindowClipRectBeforeSetChannel(window, table->BgClipRectForDrawCmd);
+    SetWindowClipRectBeforeSetChannel(window, table->Bg2ClipRectForDrawCmd);
     table->DrawSplitter.SetCurrentChannel(window->DrawList, table->Bg2DrawChannelCurrent);
 }
 
@@ -2046,7 +2046,7 @@ void ImGui::TablePopBackgroundChannel()
 // - We allocate 1 or 2 background draw channels. This is because we know TablePushBackgroundChannel() is only used for
 //   horizontal spanning. If we allowed vertical spanning we'd need one background draw channel per merge group (1-4).
 // Draw channel allocation (before merging):
-// - NoClip                       --> 2+D+1 channels: bg0/1 + bg2 + foreground (same clip rect == 1 draw call) (FIXME-TABLE: could merge bg2 and foreground?)
+// - NoClip                       --> 2+D+1 channels: bg0/1 + bg2 + foreground (same clip rect == always 1 draw call)
 // - Clip                         --> 2+D+N channels
 // - FreezeRows                   --> 2+D+N*2 (unless scrolling value is zero)
 // - FreezeRows || FreezeColunns  --> 3+D+N*2 (unless scrolling value is zero)
@@ -2085,7 +2085,8 @@ void ImGui::TableSetupDrawChannels(ImGuiTable* table)
     // All our cell highlight are manually clipped with BgClipRect. When unfreezing it will be made smaller to fit scrolling rect.
     // (This technically isn't part of setting up draw channels, but is reasonably related to be done here)
     table->BgClipRect = table->InnerClipRect;
-    table->BgClipRectForDrawCmd = table->HostClipRect;
+    table->Bg0ClipRectForDrawCmd = table->OuterWindow->ClipRect;
+    table->Bg2ClipRectForDrawCmd = table->HostClipRect;
     IM_ASSERT(table->BgClipRect.Min.y <= table->BgClipRect.Max.y);
 }
 
@@ -2288,19 +2289,17 @@ void ImGui::TableMergeDrawChannels(ImGuiTable* table)
 void ImGui::TableDrawBorders(ImGuiTable* table)
 {
     ImGuiWindow* inner_window = table->InnerWindow;
-    ImGuiWindow* outer_window = table->OuterWindow;
     table->DrawSplitter.SetCurrentChannel(inner_window->DrawList, TABLE_DRAW_CHANNEL_BG0);
     if (inner_window->Hidden || !table->HostClipRect.Overlaps(table->InnerClipRect))
         return;
     ImDrawList* inner_drawlist = inner_window->DrawList;
-    ImDrawList* outer_drawlist = outer_window->DrawList;
+    inner_drawlist->PushClipRect(table->Bg0ClipRectForDrawCmd.Min, table->Bg0ClipRectForDrawCmd.Max, false);
 
     // Draw inner border and resizing feedback
     const float border_size = TABLE_BORDER_SIZE;
     const float draw_y1 = table->InnerRect.Min.y;
     const float draw_y2_body = table->InnerRect.Max.y;
     const float draw_y2_head = table->IsUsingHeaders ? ((table->FreezeRowsCount >= 1 ? table->OuterRect.Min.y : table->WorkRect.Min.y) + table->LastFirstRowHeight) : draw_y1;
-
     if (table->Flags & ImGuiTableFlags_BordersInnerV)
     {
         for (int order_n = 0; order_n < table->ColumnsCount; order_n++)
@@ -2351,23 +2350,21 @@ void ImGui::TableDrawBorders(ImGuiTable* table)
         // parent. In inner_window, it won't reach out over scrollbars. Another weird solution would be to display part
         // of it in inner window, and the part that's over scrollbars in the outer window..)
         // Either solution currently won't allow us to use a larger border size: the border would clipped.
-        ImRect outer_border = table->OuterRect;
+        const ImRect outer_border = table->OuterRect;
         const ImU32 outer_col = table->BorderColorStrong;
-        if (inner_window != outer_window) // FIXME-TABLE
-            outer_border.Expand(1.0f);
         if ((table->Flags & ImGuiTableFlags_BordersOuter) == ImGuiTableFlags_BordersOuter)
         {
-            outer_drawlist->AddRect(outer_border.Min, outer_border.Max, outer_col, 0.0f, ~0, border_size);
+            inner_drawlist->AddRect(outer_border.Min, outer_border.Max, outer_col, 0.0f, ~0, border_size);
         }
         else if (table->Flags & ImGuiTableFlags_BordersOuterV)
         {
-            outer_drawlist->AddLine(outer_border.Min, ImVec2(outer_border.Min.x, outer_border.Max.y), outer_col, border_size);
-            outer_drawlist->AddLine(ImVec2(outer_border.Max.x, outer_border.Min.y), outer_border.Max, outer_col, border_size);
+            inner_drawlist->AddLine(outer_border.Min, ImVec2(outer_border.Min.x, outer_border.Max.y), outer_col, border_size);
+            inner_drawlist->AddLine(ImVec2(outer_border.Max.x, outer_border.Min.y), outer_border.Max, outer_col, border_size);
         }
         else if (table->Flags & ImGuiTableFlags_BordersOuterH)
         {
-            outer_drawlist->AddLine(outer_border.Min, ImVec2(outer_border.Max.x, outer_border.Min.y), outer_col, border_size);
-            outer_drawlist->AddLine(ImVec2(outer_border.Min.x, outer_border.Max.y), outer_border.Max, outer_col, border_size);
+            inner_drawlist->AddLine(outer_border.Min, ImVec2(outer_border.Max.x, outer_border.Min.y), outer_col, border_size);
+            inner_drawlist->AddLine(ImVec2(outer_border.Min.x, outer_border.Max.y), outer_border.Max, outer_col, border_size);
         }
     }
     if ((table->Flags & ImGuiTableFlags_BordersInnerH) && table->RowPosY2 < table->OuterRect.Max.y)
@@ -2377,6 +2374,8 @@ void ImGui::TableDrawBorders(ImGuiTable* table)
         if (border_y >= table->BgClipRect.Min.y && border_y < table->BgClipRect.Max.y)
             inner_drawlist->AddLine(ImVec2(table->BorderX1, border_y), ImVec2(table->BorderX2, border_y), table->BorderColorLight, border_size);
     }
+
+    inner_drawlist->PopClipRect();
 }
 
 //-------------------------------------------------------------------------
@@ -2638,7 +2637,6 @@ void ImGui::TableHeadersRow()
 // Emit a column header (text + optional sort order)
 // We cpu-clip text here so that all columns headers can be merged into a same draw call.
 // Note that because of how we cpu-clip and display sorting indicators, you _cannot_ use SameLine() after a TableHeader()
-// FIXME-TABLE: Style confusion between CellPadding.y and FramePadding.y
 void ImGui::TableHeader(const char* label)
 {
     ImGuiContext& g = *GImGui;
@@ -2660,7 +2658,7 @@ void ImGui::TableHeader(const char* label)
     ImVec2 label_pos = window->DC.CursorPos;
 
     // If we already got a row height, there's use that.
-    // FIXME-TABLE-PADDING: Problem if the correct outer-padding CellBgRect strays off our ClipRect
+    // FIXME-TABLE: Padding problem if the correct outer-padding CellBgRect strays off our ClipRect?
     ImRect cell_r = TableGetCellBgRect(table, column_n);
     float label_height = ImMax(label_size.y, table->RowMinHeight - table->CellPaddingY * 2.0f);
 
@@ -2671,7 +2669,7 @@ void ImGui::TableHeader(const char* label)
     const float ARROW_SCALE = 0.65f;
     if ((table->Flags & ImGuiTableFlags_Sortable) && !(column->Flags & ImGuiTableColumnFlags_NoSort))
     {
-        w_arrow = ImFloor(g.FontSize * ARROW_SCALE + g.Style.FramePadding.x);// table->CellPadding.x);
+        w_arrow = ImFloor(g.FontSize * ARROW_SCALE + g.Style.FramePadding.x);
         if (column->SortOrder > 0)
         {
             ImFormatString(sort_order_suf, IM_ARRAYSIZE(sort_order_suf), "%d", column->SortOrder + 1);