UI: Add support for row-aligned icon buttons in menus

This adds support for drawing icon buttons as a row in menus. This is
needed for drawing collection color tagging icons in the outliner
context menu in T77777.

Part of T77408

Differential Revision: https://developer.blender.org/D8317

3 files changed, 59 insertions, 3 deletions

diff --git a/source/blender/editors/interface/interface.c b/source/blender/editors/interface/interface.c
index 10650da4b0e..8e7fc807835 100644
--- a/source/blender/editors/interface/interface.c
+++ b/source/blender/editors/interface/interface.c
@@ -367,6 +367,12 @@ void UI_block_translate(uiBlock *block, int x, int y)
   BLI_rctf_translate(&block->rect, x, y);
 }
 
+static bool ui_but_is_row_alignment_group(const uiBut *left, const uiBut *right)
+{
+  const bool is_same_align_group = (left->alignnr && (left->alignnr == right->alignnr));
+  return is_same_align_group && (left->rect.xmin < right->rect.xmin);
+}
+
 static void ui_block_bounds_calc_text(uiBlock *block, float offset)
 {
   const uiStyle *style = UI_style_get();
@@ -385,7 +391,26 @@ static void ui_block_bounds_calc_text(uiBlock *block, float offset)
       }
     }
 
-    if (bt->next && bt->rect.xmin < bt->next->rect.xmin) {
+    /* Skip all buttons that are in a horizontal alignment group.
+     * We don't want to split them appart (but still check the row's width and apply current
+     * offsets). */
+    if (bt->next && ui_but_is_row_alignment_group(bt, bt->next)) {
+      int width = 0;
+      int alignnr = bt->alignnr;
+      for (col_bt = bt; col_bt && col_bt->alignnr == alignnr; col_bt = col_bt->next) {
+        width += BLI_rctf_size_x(&col_bt->rect);
+        col_bt->rect.xmin += x1addval;
+        col_bt->rect.xmax += x1addval;
+      }
+      if (width > i) {
+        i = width;
+      }
+      /* Give the following code the last button in the alignment group, there might have to be a
+       * split immediately after. */
+      bt = col_bt ? col_bt->prev : NULL;
+    }
+
+    if (bt && bt->next && bt->rect.xmin < bt->next->rect.xmin) {
       /* End of this column, and it's not the last one. */
       for (col_bt = init_col_bt; col_bt->prev != bt; col_bt = col_bt->next) {
         col_bt->rect.xmin = x1addval;
@@ -403,6 +428,17 @@ static void ui_block_bounds_calc_text(uiBlock *block, float offset)
 
   /* Last column. */
   for (col_bt = init_col_bt; col_bt; col_bt = col_bt->next) {
+    /* Recognize a horizontally arranged alignment group and skip its items. */
+    if (col_bt->next && ui_but_is_row_alignment_group(col_bt, col_bt->next)) {
+      int alignnr = col_bt->alignnr;
+      for (; col_bt && col_bt->alignnr == alignnr; col_bt = col_bt->next) {
+        /* pass */
+      }
+    }
+    if (!col_bt) {
+      break;
+    }
+
     col_bt->rect.xmin = x1addval;
     col_bt->rect.xmax = max_ff(x1addval + i + block->bounds, offset + block->minbounds);
 
diff --git a/source/blender/editors/interface/interface_layout.c b/source/blender/editors/interface/interface_layout.c
index a37f87e593b..f00ce7ee923 100644
--- a/source/blender/editors/interface/interface_layout.c
+++ b/source/blender/editors/interface/interface_layout.c
@@ -1434,6 +1434,26 @@ void uiItemsFullEnumO_items(uiLayout *layout,
   if (radial) {
     target = uiLayoutRadial(layout);
   }
+  else if ((uiLayoutGetLocalDir(layout) == UI_LAYOUT_HORIZONTAL) && (flag & UI_ITEM_R_ICON_ONLY)) {
+    target = layout;
+    UI_block_layout_set_current(block, target);
+
+    /* Add a blank button to the beginning of the row. */
+    uiDefIconBut(block,
+                 UI_BTYPE_LABEL,
+                 0,
+                 ICON_BLANK1,
+                 0,
+                 0,
+                 1.25f * UI_UNIT_X,
+                 UI_UNIT_Y,
+                 NULL,
+                 0,
+                 0,
+                 0,
+                 0,
+                 NULL);
+  }
   else {
     split = uiLayoutSplit(layout, 0.0f, false);
     target = uiLayoutColumn(split, layout->align);
@@ -1489,7 +1509,7 @@ void uiItemsFullEnumO_items(uiLayout *layout,
       if (item->name) {
         uiBut *but;
 
-        if (item != item_array && !radial) {
+        if (item != item_array && !radial && split) {
           target = uiLayoutColumn(split, layout->align);
 
           /* inconsistent, but menus with labels do not look good flipped */
diff --git a/source/blender/editors/interface/interface_widgets.c b/source/blender/editors/interface/interface_widgets.c
index 0cbb8f268a2..c7840aae07a 100644
--- a/source/blender/editors/interface/interface_widgets.c
+++ b/source/blender/editors/interface/interface_widgets.c
@@ -2378,7 +2378,7 @@ static void widget_draw_text_icon(const uiFontStyle *fstyle,
         rect->xmin += 0.3f * U.widget_unit;
       }
     }
-    else if (ui_block_is_menu(but->block)) {
+    else if (ui_block_is_menu(but->block) && but->alignnr == 0) {
       rect->xmin += 0.2f * U.widget_unit;
     }