Tables: added Angled headers support. Added ImGuiTableColumnFlags_AngledHeader, ImGui::TableHeadersAngledRow(), style.TableAngledHeadersAngle. (#2957)

docs/CHANGELOG.txt

@@ -94,17 +94,20 @@ Other changes:
 - Drag and Drop: Fixed submitting a tooltip from drop target location when using AcceptDragDropPayload()
   with ImGuiDragDropFlags_AcceptNoPreviewTooltip and submitting a tooltip manually.
 - TreeNode: Added ImGuiTreeNodeFlags_SpanAllColumns for use in tables. (#3151, #3565, #2451, #2438)
-- Tables: Added ImGuiTableFlags_HighlightHoveredColumn flag, currently highlighting column header.
+- Tables:
-- Tables: Fixed an edge-case when no columns are visible + table scrollbar is visible + user
+  - Added angled headers support. You need to set ImGuiTableColumnFlags_AngledHeader on selected
+    columns and call TableAngledHeadersRow(). Added style.TableAngledHeadersAngle style option.
+  - Added ImGuiTableFlags_HighlightHoveredColumn flag, currently highlighting column header.
+  - Fixed an edge-case when no columns are visible + table scrollbar is visible + user
     code is always testing return value of TableSetColumnIndex() to coarse clip. With an active
     clipper it would have asserted. Without a clipper, the scrollbar range would be wrong.
-- Tables: Request user to submit contents when outer host-window is requesting auto-resize,
+  - Request user to submit contents when outer host-window is requesting auto-resize,
     so a scrolling table can contribute to initial window size. (#6510)
-- Tables: Fixed subtle drawing overlap between borders in some situations.
+  - Fixed subtle drawing overlap between borders in some situations.
-- Tables: Fixed bottom-most and right-most outer border offset by one. (#6765, #3752) [@v-ein]
+  - Fixed bottom-most and right-most outer border offset by one. (#6765, #3752) [@v-ein]
-- Tables: Fixed top-most outer border being drawn with both TableBorderLight and TableBorderStrong
+  - Fixed top-most outer border being drawn with both TableBorderLight and TableBorderStrong
     in some situations, causing the earlier to be visible underneath when alpha is not 1.0f.
-- Tables: fixed right-clicking right-most section (past right-most column) from highlighting a column.
+  - fixed right-clicking right-most section (past right-most column) from highlighting a column.
 - TabBar: Fixed position of unsaved document marker (ImGuiTabItemFlags_UnsavedDocument) which was
   accidentally offset in 1.89.9. (#6862) [@alektron]
 - Fonts: 'float size_pixels' passed to AddFontXXX() functions is now rounded to lowest integer.

imgui.cpp

@@ -1188,6 +1188,7 @@ ImGuiStyle::ImGuiStyle()
     TabBorderSize           = 0.0f;             // Thickness of border around tabs.
     TabMinWidthForCloseButton = 0.0f;           // Minimum width for close button to appear on an unselected tab when hovered. Set to 0.0f to always show when hovering, set to FLT_MAX to never show close button unless selected.
     TabBarBorderSize        = 1.0f;             // Thickness of tab-bar separator, which takes on the tab active color to denote focus.
+    TableAngledHeadersAngle = 35.0f * (IM_PI / 180.0f); // Angle of angled headers (supported values range from -50 degrees to +50 degrees).
     ColorButtonPosition     = ImGuiDir_Right;   // Side of the color button in the ColorEdit4 widget (left/right). Defaults to ImGuiDir_Right.
     ButtonTextAlign         = ImVec2(0.5f,0.5f);// Alignment of button text when button is larger than text.
     SelectableTextAlign     = ImVec2(0.0f,0.0f);// Alignment of selectable text. Defaults to (0.0f, 0.0f) (top-left aligned). It's generally important to keep this left-aligned if you want to lay multiple items on a same line.

imgui.h

@@ -771,8 +771,9 @@ namespace ImGui
     // - Use TableSetupScrollFreeze() to lock columns/rows so they stay visible when scrolled.
     IMGUI_API void          TableSetupColumn(const char* label, ImGuiTableColumnFlags flags = 0, float init_width_or_weight = 0.0f, ImGuiID user_id = 0);
     IMGUI_API void          TableSetupScrollFreeze(int cols, int rows);         // lock columns/rows so they stay visible when scrolled.
-    IMGUI_API void          TableHeadersRow();                                  // submit all headers cells based on data provided to TableSetupColumn() + submit context menu
     IMGUI_API void          TableHeader(const char* label);                     // submit one header cell manually (rarely used)
+    IMGUI_API void          TableHeadersRow();                                  // submit a row with headers cells based on data provided to TableSetupColumn() + submit context menu
+    IMGUI_API void          TableAngledHeadersRow();                            // submit a row with angled headers for every column with the ImGuiTableColumnFlags_AngledHeader flag. MUST BE FIRST ROW.
 
     // Tables: Sorting & Miscellaneous functions
     // - Sorting: call TableGetSortSpecs() to retrieve latest sort specs for the table. NULL when not sorting.
@@ -1240,12 +1241,13 @@ enum ImGuiTableColumnFlags_
     ImGuiTableColumnFlags_NoSort                = 1 << 9,   // Disable ability to sort on this field (even if ImGuiTableFlags_Sortable is set on the table).
     ImGuiTableColumnFlags_NoSortAscending       = 1 << 10,  // Disable ability to sort in the ascending direction.
     ImGuiTableColumnFlags_NoSortDescending      = 1 << 11,  // Disable ability to sort in the descending direction.
-    ImGuiTableColumnFlags_NoHeaderLabel         = 1 << 12,  // TableHeadersRow() will not submit label for this column. Convenient for some small columns. Name will still appear in context menu.
+    ImGuiTableColumnFlags_NoHeaderLabel         = 1 << 12,  // TableHeadersRow() will not submit horizontal label for this column. Convenient for some small columns. Name will still appear in context menu or in angled headers.
     ImGuiTableColumnFlags_NoHeaderWidth         = 1 << 13,  // Disable header text width contribution to automatic column width.
     ImGuiTableColumnFlags_PreferSortAscending   = 1 << 14,  // Make the initial sort direction Ascending when first sorting on this column (default).
     ImGuiTableColumnFlags_PreferSortDescending  = 1 << 15,  // Make the initial sort direction Descending when first sorting on this column.
     ImGuiTableColumnFlags_IndentEnable          = 1 << 16,  // Use current Indent value when entering cell (default for column 0).
     ImGuiTableColumnFlags_IndentDisable         = 1 << 17,  // Ignore current Indent value when entering cell (default for columns > 0). Indentation changes _within_ the cell will still be honored.
+    ImGuiTableColumnFlags_AngledHeader          = 1 << 18,  // TableHeadersRow() will submit an angled header row for this column. Note this will add an extra row.
 
     // Output status flags, read-only via TableGetColumnFlags()
     ImGuiTableColumnFlags_IsEnabled             = 1 << 24,  // Status: is enabled == not hidden by user/api (referred to as "Hide" in _DefaultHide and _NoHide) flags.
@@ -1926,6 +1928,7 @@ struct ImGuiStyle
     float       TabBorderSize;              // Thickness of border around tabs.
     float       TabMinWidthForCloseButton;  // Minimum width for close button to appear on an unselected tab when hovered. Set to 0.0f to always show when hovering, set to FLT_MAX to never show close button unless selected.
     float       TabBarBorderSize;           // Thickness of tab-bar separator, which takes on the tab active color to denote focus.
+    float       TableAngledHeadersAngle;    // Angle of angled headers (supported values range from -50.0f degrees to +50.0f degrees).
     ImGuiDir    ColorButtonPosition;        // Side of the color button in the ColorEdit4 widget (left/right). Defaults to ImGuiDir_Right.
     ImVec2      ButtonTextAlign;            // Alignment of button text when button is larger than text. Defaults to (0.5f, 0.5f) (centered).
     ImVec2      SelectableTextAlign;        // Alignment of selectable text. Defaults to (0.0f, 0.0f) (top-left aligned). It's generally important to keep this left-aligned if you want to lay multiple items on a same line.

imgui_demo.cpp

@@ -3949,6 +3949,7 @@ static void EditTableColumnsFlags(ImGuiTableColumnFlags* p_flags)
     ImGui::CheckboxFlags("_PreferSortDescending", p_flags, ImGuiTableColumnFlags_PreferSortDescending);
     ImGui::CheckboxFlags("_IndentEnable", p_flags, ImGuiTableColumnFlags_IndentEnable); ImGui::SameLine(); HelpMarker("Default for column 0");
     ImGui::CheckboxFlags("_IndentDisable", p_flags, ImGuiTableColumnFlags_IndentDisable); ImGui::SameLine(); HelpMarker("Default for column >0");
+    ImGui::CheckboxFlags("_AngledHeader", p_flags, ImGuiTableColumnFlags_AngledHeader);
 }
 
 static void ShowTableColumnsStatusFlags(ImGuiTableColumnFlags flags)
@@ -4695,8 +4696,14 @@ static void ShowDemoWindowTables()
         ImVec2 outer_size = ImVec2(0.0f, TEXT_BASE_HEIGHT * 9);
         if (ImGui::BeginTable("table_columns_flags", column_count, flags, outer_size))
         {
+            bool has_angled_header = false;
             for (int column = 0; column < column_count; column++)
+            {
+                has_angled_header |= (column_flags[column] & ImGuiTableColumnFlags_AngledHeader) != 0;
                 ImGui::TableSetupColumn(column_names[column], column_flags[column]);
+            }
+            if (has_angled_header)
+                ImGui::TableAngledHeadersRow();
             ImGui::TableHeadersRow();
             for (int column = 0; column < column_count; column++)
                 column_flags_out[column] = ImGui::TableGetColumnFlags(column);
@@ -5182,6 +5189,56 @@ static void ShowDemoWindowTables()
         ImGui::TreePop();
     }
 
+    // Demonstrate using ImGuiTableColumnFlags_AngledHeader flag to create angled headers
+    if (open_action != -1)
+        ImGui::SetNextItemOpen(open_action != 0);
+    IMGUI_DEMO_MARKER("Tables/Angled headers");
+    if (ImGui::TreeNode("Angled headers"))
+    {
+        const char* column_names[] = { "Track", "cabasa", "ride", "smash", "tom-hi", "tom-mid", "tom-low", "hihat-o", "hihat-c", "snare-s", "snare-c", "clap", "rim", "kick" };
+        const int columns_count = IM_ARRAYSIZE(column_names);
+        const int rows_count = 12;
+
+        static ImGuiTableFlags table_flags = ImGuiTableFlags_SizingFixedFit | ImGuiTableFlags_ScrollX | ImGuiTableFlags_ScrollY | ImGuiTableFlags_BordersOuter | ImGuiTableFlags_BordersInnerH | ImGuiTableFlags_Hideable | ImGuiTableFlags_Resizable | ImGuiTableFlags_Reorderable | ImGuiTableFlags_HighlightHoveredColumn;
+        static bool bools[columns_count * rows_count] = {}; // Dummy storage selection storage
+        static int frozen_rows = 2;
+        ImGui::CheckboxFlags("_ScrollX", &table_flags, ImGuiTableFlags_ScrollX);
+        ImGui::CheckboxFlags("_ScrollY", &table_flags, ImGuiTableFlags_ScrollY);
+        ImGui::CheckboxFlags("_NoBordersInBody", &table_flags, ImGuiTableFlags_NoBordersInBody);
+        ImGui::CheckboxFlags("_HighlightHoveredColumn", &table_flags, ImGuiTableFlags_HighlightHoveredColumn);
+        ImGui::SetNextItemWidth(ImGui::GetFontSize() * 8);
+        ImGui::SliderInt("Frozen rows", &frozen_rows, 0, 2);
+
+        if (ImGui::BeginTable("table_angled_headers", columns_count, table_flags, ImVec2(0.0f, TEXT_BASE_HEIGHT * 12)))
+        {
+            ImGui::TableSetupColumn(column_names[0], ImGuiTableColumnFlags_NoHide | ImGuiTableColumnFlags_NoReorder);
+            for (int n = 1; n < columns_count; n++)
+                ImGui::TableSetupColumn(column_names[n], ImGuiTableColumnFlags_AngledHeader | ImGuiTableColumnFlags_WidthFixed);
+            ImGui::TableSetupScrollFreeze(0, frozen_rows);
+
+            ImGui::TableAngledHeadersRow(); // Draw angled headers for all columns with the ImGuiTableColumnFlags_AngledHeader flag.
+            ImGui::TableHeadersRow();       // Draw remaining headers and allow access to context-menu and other functions.
+            for (int row = 0; row < rows_count; row++)
+            {
+                ImGui::PushID(row);
+                ImGui::TableNextRow();
+                ImGui::TableSetColumnIndex(0);
+                ImGui::AlignTextToFramePadding();
+                ImGui::Text("Track %d", row);
+                for (int column = 1; column < columns_count; column++)
+                    if (ImGui::TableSetColumnIndex(column))
+                    {
+                        ImGui::PushID(column);
+                        ImGui::Checkbox("", &bools[row * columns_count + column]);
+                        ImGui::PopID();
+                    }
+                ImGui::PopID();
+            }
+            ImGui::EndTable();
+        }
+        ImGui::TreePop();
+    }
+
     // Demonstrate creating custom context menus inside columns, while playing it nice with context menus provided by TableHeadersRow()/TableHeader()
     if (open_action != -1)
         ImGui::SetNextItemOpen(open_action != 0);
@@ -5428,6 +5485,7 @@ static void ShowDemoWindowTables()
             | ImGuiTableFlags_RowBg | ImGuiTableFlags_Borders | ImGuiTableFlags_NoBordersInBody
             | ImGuiTableFlags_ScrollX | ImGuiTableFlags_ScrollY
             | ImGuiTableFlags_SizingFixedFit;
+        static ImGuiTableColumnFlags columns_base_flags = ImGuiTableColumnFlags_None;
 
         enum ContentsType { CT_Text, CT_Button, CT_SmallButton, CT_FillButton, CT_Selectable, CT_SelectableSpanRow };
         static int contents_type = CT_SelectableSpanRow;
@@ -5525,6 +5583,8 @@ static void ShowDemoWindowTables()
             {
                 ImGui::Checkbox("show_headers", &show_headers);
                 ImGui::CheckboxFlags("ImGuiTableFlags_HighlightHoveredColumn", &flags, ImGuiTableFlags_HighlightHoveredColumn);
+                ImGui::CheckboxFlags("ImGuiTableColumnFlags_AngledHeader", &columns_base_flags, ImGuiTableColumnFlags_AngledHeader);
+                ImGui::SameLine(); HelpMarker("Enable AngledHeader on all columns. Best enabled on selected narrow columns (see \"Angled headers\" section of the demo).");
                 ImGui::TreePop();
             }
 
@@ -5590,12 +5650,12 @@ static void ShowDemoWindowTables()
             // Declare columns
             // We use the "user_id" parameter of TableSetupColumn() to specify a user id that will be stored in the sort specifications.
             // This is so our sort function can identify a column given our own identifier. We could also identify them based on their index!
-            ImGui::TableSetupColumn("ID",           ImGuiTableColumnFlags_DefaultSort | ImGuiTableColumnFlags_WidthFixed | ImGuiTableColumnFlags_NoHide, 0.0f, MyItemColumnID_ID);
+            ImGui::TableSetupColumn("ID",           columns_base_flags | ImGuiTableColumnFlags_DefaultSort | ImGuiTableColumnFlags_WidthFixed | ImGuiTableColumnFlags_NoHide, 0.0f, MyItemColumnID_ID);
-            ImGui::TableSetupColumn("Name",         ImGuiTableColumnFlags_WidthFixed, 0.0f, MyItemColumnID_Name);
+            ImGui::TableSetupColumn("Name",         columns_base_flags | ImGuiTableColumnFlags_WidthFixed, 0.0f, MyItemColumnID_Name);
-            ImGui::TableSetupColumn("Action",       ImGuiTableColumnFlags_NoSort | ImGuiTableColumnFlags_WidthFixed, 0.0f, MyItemColumnID_Action);
+            ImGui::TableSetupColumn("Action",       columns_base_flags | ImGuiTableColumnFlags_NoSort | ImGuiTableColumnFlags_WidthFixed, 0.0f, MyItemColumnID_Action);
-            ImGui::TableSetupColumn("Quantity",     ImGuiTableColumnFlags_PreferSortDescending, 0.0f, MyItemColumnID_Quantity);
+            ImGui::TableSetupColumn("Quantity",     columns_base_flags | ImGuiTableColumnFlags_PreferSortDescending, 0.0f, MyItemColumnID_Quantity);
-            ImGui::TableSetupColumn("Description",  (flags & ImGuiTableFlags_NoHostExtendX) ? 0 : ImGuiTableColumnFlags_WidthStretch, 0.0f, MyItemColumnID_Description);
+            ImGui::TableSetupColumn("Description",  columns_base_flags | ((flags & ImGuiTableFlags_NoHostExtendX) ? 0 : ImGuiTableColumnFlags_WidthStretch), 0.0f, MyItemColumnID_Description);
-            ImGui::TableSetupColumn("Hidden",       ImGuiTableColumnFlags_DefaultHide | ImGuiTableColumnFlags_NoSort);
+            ImGui::TableSetupColumn("Hidden",       columns_base_flags |  ImGuiTableColumnFlags_DefaultHide | ImGuiTableColumnFlags_NoSort);
             ImGui::TableSetupScrollFreeze(freeze_cols, freeze_rows);
 
             // Sort our data if sort specs have been changed!
@@ -5614,6 +5674,8 @@ static void ShowDemoWindowTables()
             const bool sorts_specs_using_quantity = (ImGui::TableGetColumnFlags(3) & ImGuiTableColumnFlags_IsSorted) != 0;
 
             // Show headers
+            if (show_headers && (columns_base_flags & ImGuiTableColumnFlags_AngledHeader) != 0)
+                ImGui::TableAngledHeadersRow();
             if (show_headers)
                 ImGui::TableHeadersRow();
 
@@ -6400,7 +6462,6 @@ void ImGui::ShowStyleEditor(ImGuiStyle* ref)
             ImGui::SeparatorText("Main");
             ImGui::SliderFloat2("WindowPadding", (float*)&style.WindowPadding, 0.0f, 20.0f, "%.0f");
             ImGui::SliderFloat2("FramePadding", (float*)&style.FramePadding, 0.0f, 20.0f, "%.0f");
-            ImGui::SliderFloat2("CellPadding", (float*)&style.CellPadding, 0.0f, 20.0f, "%.0f");
             ImGui::SliderFloat2("ItemSpacing", (float*)&style.ItemSpacing, 0.0f, 20.0f, "%.0f");
             ImGui::SliderFloat2("ItemInnerSpacing", (float*)&style.ItemInnerSpacing, 0.0f, 20.0f, "%.0f");
             ImGui::SliderFloat2("TouchExtraPadding", (float*)&style.TouchExtraPadding, 0.0f, 10.0f, "%.0f");
@@ -6425,6 +6486,10 @@ void ImGui::ShowStyleEditor(ImGuiStyle* ref)
             ImGui::SliderFloat("GrabRounding", &style.GrabRounding, 0.0f, 12.0f, "%.0f");
             ImGui::SliderFloat("TabRounding", &style.TabRounding, 0.0f, 12.0f, "%.0f");
 
+            ImGui::SeparatorText("Tables");
+            ImGui::SliderFloat2("CellPadding", (float*)&style.CellPadding, 0.0f, 20.0f, "%.0f");
+            ImGui::SliderAngle("TableAngledHeadersAngle", &style.TableAngledHeadersAngle, -50.0f, +50.0f);
+
             ImGui::SeparatorText("Widgets");
             ImGui::SliderFloat2("WindowTitleAlign", (float*)&style.WindowTitleAlign, 0.0f, 1.0f, "%.2f");
             int window_menu_button_position = style.WindowMenuButtonPosition + 1;

imgui_draw.cpp

@@ -1989,6 +1989,14 @@ void ImGui::ShadeVertsLinearUV(ImDrawList* draw_list, int vert_start_idx, int ve
     }
 }
 
+void ImGui::ShadeVertsTransformPos(ImDrawList* draw_list, int vert_start_idx, int vert_end_idx, const ImVec2& pivot_in, float cos_a, float sin_a, const ImVec2& pivot_out)
+{
+    ImDrawVert* vert_start = draw_list->VtxBuffer.Data + vert_start_idx;
+    ImDrawVert* vert_end = draw_list->VtxBuffer.Data + vert_end_idx;
+    for (ImDrawVert* vertex = vert_start; vertex < vert_end; ++vertex)
+        vertex->pos = ImRotate(vertex->pos- pivot_in, cos_a, sin_a) + pivot_out;
+}
+
 //-----------------------------------------------------------------------------
 // [SECTION] ImFontConfig
 //-----------------------------------------------------------------------------

imgui_internal.h

@@ -2731,6 +2731,8 @@ struct IMGUI_API ImGuiTable
     float                       ResizedColumnNextWidth;
     float                       ResizeLockMinContentsX2;    // Lock minimum contents width while resizing down in order to not create feedback loops. But we allow growing the table.
     float                       RefScale;                   // Reference scale to be able to rescale columns on font/dpi changes.
+    float                       AngledHeadersHeight;        // Set by TableAngledHeadersRow(), used in TableUpdateLayout()
+    float                       AngledHeadersSlope;         // Set by TableAngledHeadersRow(), used in TableUpdateLayout()
     ImRect                      OuterRect;                  // Note: for non-scrolling table, OuterRect.Max.y is often FLT_MAX until EndTable(), unless a height has been specified in BeginTable().
     ImRect                      InnerRect;                  // InnerRect but without decoration. As with OuterRect, for non-scrolling tables, InnerRect.Max.y is
     ImRect                      WorkRect;
@@ -2753,6 +2755,7 @@ struct IMGUI_API ImGuiTable
     ImGuiTableColumnIdx         ColumnsEnabledCount;        // Number of enabled columns (<= ColumnsCount)
     ImGuiTableColumnIdx         ColumnsEnabledFixedCount;   // Number of enabled columns (<= ColumnsCount)
     ImGuiTableColumnIdx         DeclColumnsCount;           // Count calls to TableSetupColumn()
+    ImGuiTableColumnIdx         AngledHeadersCount;         // Count columns with angled headers
     ImGuiTableColumnIdx         HoveredColumnBody;          // Index of column whose visible region is being hovered. Important: == ColumnsCount when hovering empty region after the right-most column!
     ImGuiTableColumnIdx         HoveredColumnBorder;        // Index of column whose right-border is being hovered (for resizing).
     ImGuiTableColumnIdx         HighlightColumnHeader;      // Index of column which should be highlighted.
@@ -2802,11 +2805,12 @@ struct IMGUI_API ImGuiTable
 // Transient data that are only needed between BeginTable() and EndTable(), those buffers are shared (1 per level of stacked table).
 // - Accessing those requires chasing an extra pointer so for very frequently used data we leave them in the main table structure.
 // - We also leave out of this structure data that tend to be particularly useful for debugging/metrics.
-// sizeof() ~ 112 bytes.
+// sizeof() ~ 120 bytes.
 struct IMGUI_API ImGuiTableTempData
 {
     int                         TableIndex;                 // Index in g.Tables.Buf[] pool
     float                       LastTimeActive;             // Last timestamp this structure was used
+    float                       AngledheadersExtraWidth;    // Used in EndTable()
 
     ImVec2                      UserOuterSize;              // outer_size.x passed to BeginTable()
     ImDrawListSplitter          DrawSplitter;
@@ -3177,8 +3181,10 @@ namespace ImGui
     IMGUI_API int           TableGetHoveredColumn();    // May use (TableGetColumnFlags() & ImGuiTableColumnFlags_IsHovered) instead. Return hovered column. return -1 when table is not hovered. return columns_count if the unused space at the right of visible columns is hovered.
     IMGUI_API int           TableGetHoveredRow();       // Retrieve *PREVIOUS FRAME* hovered row. This difference with TableGetHoveredColumn() is the reason why this is not public yet.
     IMGUI_API float         TableGetHeaderRowHeight();
+    IMGUI_API float         TableGetHeaderAngledMaxLabelWidth();
     IMGUI_API void          TablePushBackgroundChannel();
     IMGUI_API void          TablePopBackgroundChannel();
+    IMGUI_API void          TableAngledHeadersRowEx(float angle, float label_width = 0.0f);
 
     // Tables: Internals
     inline    ImGuiTable*   GetCurrentTable() { ImGuiContext& g = *GImGui; return g.CurrentTable; }
@@ -3336,6 +3342,7 @@ namespace ImGui
     // Shade functions (write over already created vertices)
     IMGUI_API void          ShadeVertsLinearColorGradientKeepAlpha(ImDrawList* draw_list, int vert_start_idx, int vert_end_idx, ImVec2 gradient_p0, ImVec2 gradient_p1, ImU32 col0, ImU32 col1);
     IMGUI_API void          ShadeVertsLinearUV(ImDrawList* draw_list, int vert_start_idx, int vert_end_idx, const ImVec2& a, const ImVec2& b, const ImVec2& uv_a, const ImVec2& uv_b, bool clamp);
+    IMGUI_API void          ShadeVertsTransformPos(ImDrawList* draw_list, int vert_start_idx, int vert_end_idx, const ImVec2& pivot_in, float cos_a, float sin_a, const ImVec2& pivot_out);
 
     // Garbage collection
     IMGUI_API void          GcCompactTransientMiscBuffers();

imgui_tables.cpp

@@ -478,9 +478,10 @@ bool    ImGui::BeginTableEx(const char* name, ImGuiID id, int columns_count, ImG
     table->FreezeRowsRequest = table->FreezeRowsCount = 0; // This will be setup by TableSetupScrollFreeze(), if any
     table->FreezeColumnsRequest = table->FreezeColumnsCount = 0;
     table->IsUnfrozenRows = true;
-    table->DeclColumnsCount = 0;
+    table->DeclColumnsCount = table->AngledHeadersCount = 0;
     if (previous_frame_active + 1 < g.FrameCount)
         table->IsActiveIdInTable = false;
+    temp_data->AngledheadersExtraWidth = 0.0f;
 
     // Using opaque colors facilitate overlapping lines of the grid, otherwise we'd need to improve TableDrawBorders()
     table->BorderColorStrong = GetColorU32(ImGuiCol_TableBorderStrong);
@@ -984,6 +985,12 @@ void ImGui::TableUpdateLayout(ImGuiTable* table)
     const bool is_hovering_table = ItemHoverable(mouse_hit_rect, 0, ImGuiItemFlags_None);
     g.ActiveId = backup_active_id;
 
+    // Determine skewed MousePos.x to support angled headers.
+    float mouse_skewed_x = g.IO.MousePos.x;
+    if (table->AngledHeadersHeight > 0.0f)
+        if (g.IO.MousePos.y >= table->OuterRect.Min.y && g.IO.MousePos.y <= table->OuterRect.Min.y + table->AngledHeadersHeight)
+            mouse_skewed_x += ImTrunc((table->OuterRect.Min.y + table->AngledHeadersHeight - g.IO.MousePos.y) * table->AngledHeadersSlope);
+
     // [Part 6] Setup final position, offset, skip/clip states and clipping rectangles, detect hovered column
     // Process columns in their visible orders as we are comparing the visible order and adjusting host_clip_rect while looping.
     int visible_n = 0;
@@ -1025,7 +1032,7 @@ void ImGui::TableUpdateLayout(ImGuiTable* table)
         }
 
         // Detect hovered column
-        if (is_hovering_table && g.IO.MousePos.x >= column->ClipRect.Min.x && g.IO.MousePos.x < column->ClipRect.Max.x)
+        if (is_hovering_table && mouse_skewed_x >= column->ClipRect.Min.x && mouse_skewed_x < column->ClipRect.Max.x)
             table->HoveredColumnBody = (ImGuiTableColumnIdx)column_n;
 
         // Lock start position
@@ -1124,7 +1131,7 @@ void ImGui::TableUpdateLayout(ImGuiTable* table)
     // because of using _WidthAuto/_WidthStretch). This will hide the resizing option from the context menu.
     const float unused_x1 = ImMax(table->WorkRect.Min.x, table->Columns[table->RightMostEnabledColumn].ClipRect.Max.x);
     if (is_hovering_table && table->HoveredColumnBody == -1)
-        if (g.IO.MousePos.x >= unused_x1)
+        if (mouse_skewed_x >= unused_x1)
             table->HoveredColumnBody = (ImGuiTableColumnIdx)table->ColumnsCount;
     if (has_resizable == false && (table->Flags & ImGuiTableFlags_Resizable))
         table->Flags &= ~ImGuiTableFlags_Resizable;
@@ -1211,7 +1218,7 @@ void ImGui::TableUpdateBorders(ImGuiTable* table)
     // Actual columns highlight/render will be performed in EndTable() and not be affected.
     ImGuiTableInstanceData* table_instance = TableGetInstanceData(table, table->InstanceCurrent);
     const float hit_half_width = TABLE_RESIZE_SEPARATOR_HALF_THICKNESS;
-    const float hit_y1 = table->OuterRect.Min.y;
+    const float hit_y1 = (table->FreezeRowsCount >= 1 ? table->OuterRect.Min.y : table->WorkRect.Min.y) + table->AngledHeadersHeight;
     const float hit_y2_body = ImMax(table->OuterRect.Max.y, hit_y1 + table_instance->LastOuterHeight);
     const float hit_y2_head = hit_y1 + table_instance->LastTopHeadersRowHeight;
 
@@ -1316,7 +1323,7 @@ void    ImGui::EndTable()
             max_pos_x = ImMax(max_pos_x, table->Columns[table->RightMostEnabledColumn].WorkMaxX + table->CellPaddingX + table->OuterPaddingX - outer_padding_for_border);
         if (table->ResizedColumn != -1)
             max_pos_x = ImMax(max_pos_x, table->ResizeLockMinContentsX2);
-        table->InnerWindow->DC.CursorMaxPos.x = max_pos_x;
+        table->InnerWindow->DC.CursorMaxPos.x = max_pos_x + table->TempData->AngledheadersExtraWidth;
     }
 
     // Pop clipping rect
@@ -1434,7 +1441,7 @@ void    ImGui::EndTable()
     }
     else if (temp_data->UserOuterSize.x <= 0.0f)
     {
-        const float decoration_size = (table->Flags & ImGuiTableFlags_ScrollX) ? inner_window->ScrollbarSizes.x : 0.0f;
+        const float decoration_size = table->TempData->AngledheadersExtraWidth + ((table->Flags & ImGuiTableFlags_ScrollX) ? inner_window->ScrollbarSizes.x : 0.0f);
         outer_window->DC.IdealMaxPos.x = ImMax(outer_window->DC.IdealMaxPos.x, table->OuterRect.Min.x + table->ColumnsAutoFitWidth + decoration_size - temp_data->UserOuterSize.x);
         outer_window->DC.CursorMaxPos.x = ImMax(backup_outer_max_pos.x, ImMin(table->OuterRect.Max.x, table->OuterRect.Min.x + table->ColumnsAutoFitWidth));
     }
@@ -1501,6 +1508,11 @@ void ImGui::TableSetupColumn(const char* label, ImGuiTableColumnFlags flags, flo
     if ((flags & ImGuiTableColumnFlags_WidthMask_) == 0 && init_width_or_weight > 0.0f)
         if ((table->Flags & ImGuiTableFlags_SizingMask_) == ImGuiTableFlags_SizingFixedFit || (table->Flags & ImGuiTableFlags_SizingMask_) == ImGuiTableFlags_SizingFixedSame)
             flags |= ImGuiTableColumnFlags_WidthFixed;
+    if (flags & ImGuiTableColumnFlags_AngledHeader)
+    {
+        flags |= ImGuiTableColumnFlags_NoHeaderLabel;
+        table->AngledHeadersCount++;
+    }
 
     TableSetupColumnFlags(table, column, flags);
     column->UserID = user_id;
@@ -2623,7 +2635,7 @@ void ImGui::TableDrawBorders(ImGuiTable* table)
     // Draw inner border and resizing feedback
     ImGuiTableInstanceData* table_instance = TableGetInstanceData(table, table->InstanceCurrent);
     const float border_size = TABLE_BORDER_SIZE;
-    const float draw_y1 = table->InnerRect.Min.y + ((table->Flags & ImGuiTableFlags_BordersOuterH) ? 1.0f : 0.0f);
+    const float draw_y1 = ImMax(table->InnerRect.Min.y, (table->FreezeRowsCount >= 1 ? table->InnerRect.Min.y : table->WorkRect.Min.y) + table->AngledHeadersHeight) + ((table->Flags & ImGuiTableFlags_BordersOuterH) ? 1.0f : 0.0f);
     const float draw_y2_body = table->InnerRect.Max.y;
     const float draw_y2_head = table->IsUsingHeaders ? ImMin(table->InnerRect.Max.y, (table->FreezeRowsCount >= 1 ? table->InnerRect.Min.y : table->WorkRect.Min.y) + table_instance->LastTopHeadersRowHeight) : draw_y1;
     if (table->Flags & ImGuiTableFlags_BordersInnerV)
@@ -2896,6 +2908,8 @@ void ImGui::TableSortSpecsBuild(ImGuiTable* table)
 // - TableGetHeaderRowHeight() [Internal]
 // - TableHeadersRow()
 // - TableHeader()
+// - TableAngledHeadersRow()
+// - TableAngledHeadersRowEx() [Internal]
 //-------------------------------------------------------------------------
 
 float ImGui::TableGetHeaderRowHeight()
@@ -2914,6 +2928,18 @@ float ImGui::TableGetHeaderRowHeight()
     return row_height + g.Style.CellPadding.y * 2.0f;
 }
 
+float ImGui::TableGetHeaderAngledMaxLabelWidth()
+{
+    ImGuiContext& g = *GImGui;
+    ImGuiTable* table = g.CurrentTable;
+    float width = 0.0f;
+    for (int column_n = 0; column_n < table->ColumnsCount; column_n++)
+        if (IM_BITARRAY_TESTBIT(table->EnabledMaskByIndex, column_n))
+            if (table->Columns[column_n].Flags & ImGuiTableColumnFlags_AngledHeader)
+                width = ImMax(width, CalcTextSize(TableGetColumnName(table, column_n), NULL, true).x);
+    return width + g.Style.CellPadding.x * 2.0f;
+}
+
 // [Public] This is a helper to output TableHeader() calls based on the column names declared in TableSetupColumn().
 // The intent is that advanced users willing to create customized headers would not need to use this helper
 // and can create their own! For example: TableHeader() may be preceeded by Checkbox() or other custom widgets.
@@ -3098,6 +3124,115 @@ void ImGui::TableHeader(const char* label)
         TableOpenContextMenu(column_n);
 }
 
+// Unlike TableHeadersRow() it is not expected that you can reimplement or customize this with custom widgets.
+// FIXME: highlight without ImGuiTableFlags_HighlightHoveredColumn
+// FIXME: No hit-testing/button on the angled header.
+void ImGui::TableAngledHeadersRow()
+{
+    ImGuiContext& g = *GImGui;
+    TableAngledHeadersRowEx(g.Style.TableAngledHeadersAngle, 0.0f);
+}
+
+void ImGui::TableAngledHeadersRowEx(float angle, float max_label_width)
+{
+    ImGuiContext& g = *GImGui;
+    ImGuiTable* table = g.CurrentTable;
+    ImGuiWindow* window = g.CurrentWindow;
+    ImDrawList* draw_list = window->DrawList;
+    IM_ASSERT(table != NULL && "Need to call TableHeadersRow() after BeginTable()!");
+    IM_ASSERT(table->CurrentRow == -1 && "Must be first row");
+
+    if (max_label_width == 0.0f)
+        max_label_width = TableGetHeaderAngledMaxLabelWidth();
+
+    // Angle argument expressed in (-IM_PI/2 .. +IM_PI/2) as it is easier to think about for user.
+    const bool flip_label = (angle < 0.0f);
+    angle -= IM_PI * 0.5f;
+    const float cos_a = ImCos(angle);
+    const float sin_a = ImSin(angle);
+    const float label_cos_a = flip_label ? ImCos(angle + IM_PI) : cos_a;
+    const float label_sin_a = flip_label ? ImSin(angle + IM_PI) : sin_a;
+    const ImVec2 unit_right = ImVec2(cos_a, sin_a);
+
+    // Calculate our base metrics and set angled headers data _before_ the first call to TableNextRow()
+    // FIXME-STYLE: Would it be better for user to submit 'max_label_width' or 'row_height' ? One can be derived from the other.
+    const float header_height = table->RowCellPaddingY * 2.0f + g.FontSize;
+    const float row_height = ImFabs(ImRotate(ImVec2(max_label_width, flip_label ? +header_height : -header_height), cos_a, sin_a).y);
+    const ImVec2 header_angled_vector = unit_right * (row_height / -sin_a);
+    table->AngledHeadersHeight = row_height;
+    table->AngledHeadersSlope = (sin_a != 0.0f) ? (cos_a / sin_a) : 0.0f;
+
+    // Declare row, override and draw our own background
+    TableNextRow(ImGuiTableRowFlags_Headers, row_height);
+    TableNextColumn();
+    table->DrawSplitter->SetCurrentChannel(draw_list, TABLE_DRAW_CHANNEL_BG0);
+    PushClipRect(table->BgClipRect.Min, table->BgClipRect.Max, false); // Span all columns
+    TableSetBgColor(ImGuiTableBgTarget_RowBg0, 0); // Cancel
+    draw_list->AddRectFilled(table->BgClipRect.Min, table->BgClipRect.Max, GetColorU32(ImGuiCol_TableHeaderBg, 0.25f)); // FIXME-STYLE: Change row background with an arbitrary color.
+
+    const ImRect row_r(table->WorkRect.Min.x, table->BgClipRect.Min.y, table->WorkRect.Max.x, window->DC.CursorPos.y + row_height);
+    const ImGuiID row_id = GetID("##AngledHeaders");
+    ButtonBehavior(row_r, row_id, NULL, NULL);
+    KeepAliveID(row_id);
+
+    ImGuiTableInstanceData* table_instance = TableGetInstanceData(table, table->InstanceCurrent);
+    int highlight_column_n = table->HighlightColumnHeader;
+    if (highlight_column_n == -1 && table->HoveredColumnBody != -1)
+        if (table_instance->HoveredRowLast == 0 && table->HoveredColumnBorder == -1 && (g.ActiveId == 0 || g.ActiveId == row_id || (table->IsActiveIdInTable || g.DragDropActive)))
+            highlight_column_n = table->HoveredColumnBody;
+
+    float max_x = 0.0f;
+    for (int pass = 0; pass < 2; pass++)
+        for (int order_n = 0; order_n < table->ColumnsCount; order_n++)
+        {
+            if (!IM_BITARRAY_TESTBIT(table->EnabledMaskByDisplayOrder, order_n))
+                continue;
+            const int column_n = table->DisplayOrderToIndex[order_n];
+            ImGuiTableColumn* column = &table->Columns[column_n];
+            if ((column->Flags & ImGuiTableColumnFlags_AngledHeader) == 0) // Note: can't rely on ImGuiTableColumnFlags_IsVisible test here.
+                continue;
+
+            ImVec2 bg_shape[4];
+            bg_shape[0] = ImVec2(column->MaxX, row_r.Max.y);
+            bg_shape[1] = ImVec2(column->MinX, row_r.Max.y);
+            bg_shape[2] = bg_shape[1] + header_angled_vector;
+            bg_shape[3] = bg_shape[0] + header_angled_vector;
+            if (pass == 0)
+            {
+                // Draw shape
+                draw_list->AddQuadFilled(bg_shape[0], bg_shape[1], bg_shape[2], bg_shape[3], GetColorU32(ImGuiCol_TableHeaderBg));
+                if (column_n == highlight_column_n)
+                    draw_list->AddQuadFilled(bg_shape[0], bg_shape[1], bg_shape[2], bg_shape[3], GetColorU32(ImGuiCol_Header)); // Highlight on hover
+                //draw_list->AddQuad(bg_shape[0], bg_shape[1], bg_shape[2], bg_shape[3], GetColorU32(ImGuiCol_TableBorderLight), 1.0f);
+                max_x = ImMax(max_x, bg_shape[3].x);
+
+                // Draw label (first draw at an offset where RenderTextXXX() function won't meddle with applying current ClipRect, then transform to final offset)
+                // FIXME: May be worth tidying up all those operations to make them easier to understand.
+                const char* label_name = TableGetColumnName(table, column_n);
+                const float clip_width = max_label_width - (sin_a * table->RowCellPaddingY);
+                ImRect label_r(window->ClipRect.Min, window->ClipRect.Min + ImVec2(clip_width + (flip_label ? 0.0f : table->CellPaddingX), header_height + table->RowCellPaddingY));
+                ImVec2 label_size = CalcTextSize(label_name, NULL, true);
+                ImVec2 label_off = ImVec2(flip_label ? ImMax(0.0f, max_label_width - label_size.x - table->CellPaddingX) : table->CellPaddingX, table->RowCellPaddingY);
+                int vtx_idx_begin = draw_list->_VtxCurrentIdx;
+                RenderTextEllipsis(draw_list, label_r.Min + label_off, label_r.Max, label_r.Max.x, label_r.Max.x, label_name, NULL, &label_size);
+                //if (g.IO.KeyShift) { draw_list->AddRect(label_r.Min, label_r.Max, IM_COL32(0, 255, 0, 255), 0.0f, 0, 2.0f); }
+                int vtx_idx_end = draw_list->_VtxCurrentIdx;
+
+                // Rotate and offset label
+                ImVec2 pivot_in = label_r.GetBL();
+                ImVec2 pivot_out = ImVec2(column->WorkMinX, row_r.Max.y) + (flip_label ? (unit_right * clip_width) : ImVec2(header_height, 0.0f));
+                ShadeVertsTransformPos(draw_list, vtx_idx_begin, vtx_idx_end, pivot_in, label_cos_a, label_sin_a, pivot_out); // Rotate and offset
+            }
+            if (pass == 1)
+            {
+                // Draw border
+                draw_list->AddLine(bg_shape[0], bg_shape[3], TableGetColumnBorderCol(table, order_n, column_n));
+            }
+        }
+    PopClipRect();
+    table->TempData->AngledheadersExtraWidth = ImMax(0.0f, max_x - table->Columns[table->RightMostEnabledColumn].MaxX);
+}
+
 //-------------------------------------------------------------------------
 // [SECTION] Tables: Context Menu
 //-------------------------------------------------------------------------