UI Code Quality: Use derived struct for color buttons

For the main rationale behind this design, see 03b122e2a18df. Further,
this removes users of `uiBut.a1`/`uiBut.a2`, which is a very ugly design
choice (hard to reason about).

Part of Part of T74432.

7 files changed, 50 insertions, 41 deletions

diff --git a/source/blender/editors/include/UI_interface.h b/source/blender/editors/include/UI_interface.h
index 4a98d72a463..e8352bc6b21 100644
--- a/source/blender/editors/include/UI_interface.h
+++ b/source/blender/editors/include/UI_interface.h
@@ -390,8 +390,6 @@ enum {
   UI_GRAD_L_ALT = 10,
 };
 
-#define UI_PALETTE_COLOR 20
-
 /* Drawing
  *
  * Functions to draw various shapes, taking theme settings into account.
diff --git a/source/blender/editors/interface/interface.c b/source/blender/editors/interface/interface.c
index 9a4eb73c20e..0d8f682ea51 100644
--- a/source/blender/editors/interface/interface.c
+++ b/source/blender/editors/interface/interface.c
@@ -2329,7 +2329,8 @@ bool ui_but_supports_cycling(const uiBut *but)
 {
   return ((ELEM(but->type, UI_BTYPE_ROW, UI_BTYPE_NUM, UI_BTYPE_NUM_SLIDER, UI_BTYPE_LISTBOX)) ||
           (but->type == UI_BTYPE_MENU && ui_but_menu_step_poll(but)) ||
-          (but->type == UI_BTYPE_COLOR && but->a1 != -1) || (but->menu_step_func != NULL));
+          (but->type == UI_BTYPE_COLOR && ((uiButColor *)but)->is_pallete_color) ||
+          (but->menu_step_func != NULL));
 }
 
 double ui_but_value_get(uiBut *but)
@@ -3772,6 +3773,10 @@ static void ui_but_alloc_info(const eButType type,
   bool has_custom_type = true;
 
   switch (type) {
+    case UI_BTYPE_COLOR:
+      alloc_size = sizeof(uiButColor);
+      alloc_str = "uiButColor";
+      break;
     case UI_BTYPE_DECORATOR:
       alloc_size = sizeof(uiButDecorator);
       alloc_str = "uiButDecorator";
diff --git a/source/blender/editors/interface/interface_handlers.c b/source/blender/editors/interface/interface_handlers.c
index f55d8d5ccc6..999ddca65b9 100644
--- a/source/blender/editors/interface/interface_handlers.c
+++ b/source/blender/editors/interface/interface_handlers.c
@@ -5713,21 +5713,24 @@ static bool ui_numedit_but_UNITVEC(
   return changed;
 }
 
-static void ui_palette_set_active(uiBut *but)
+static void ui_palette_set_active(uiButColor *color_but)
 {
-  if ((int)(but->a1) == UI_PALETTE_COLOR) {
-    Palette *palette = (Palette *)but->rnapoin.owner_id;
-    PaletteColor *color = but->rnapoin.data;
+  if (color_but->is_pallete_color) {
+    Palette *palette = (Palette *)color_but->but.rnapoin.owner_id;
+    PaletteColor *color = color_but->but.rnapoin.data;
     palette->active_color = BLI_findindex(&palette->colors, color);
   }
 }
 
 static int ui_do_but_COLOR(bContext *C, uiBut *but, uiHandleButtonData *data, const wmEvent *event)
 {
+  BLI_assert(but->type == UI_BTYPE_COLOR);
+  uiButColor *color_but = (uiButColor *)but;
+
   if (data->state == BUTTON_STATE_HIGHLIGHT) {
     /* first handle click on icondrag type button */
     if (event->type == LEFTMOUSE && but->dragpoin && event->val == KM_PRESS) {
-      ui_palette_set_active(but);
+      ui_palette_set_active(color_but);
       if (ui_but_contains_point_px_icon(but, data->region, event)) {
         button_activate_state(C, but, BUTTON_STATE_WAIT_DRAG);
         data->dragstartx = event->x;
@@ -5737,7 +5740,7 @@ static int ui_do_but_COLOR(bContext *C, uiBut *but, uiHandleButtonData *data, co
     }
 #ifdef USE_DRAG_TOGGLE
     if (event->type == LEFTMOUSE && event->val == KM_PRESS) {
-      ui_palette_set_active(but);
+      ui_palette_set_active(color_but);
       button_activate_state(C, but, BUTTON_STATE_WAIT_DRAG);
       data->dragstartx = event->x;
       data->dragstarty = event->y;
@@ -5746,7 +5749,7 @@ static int ui_do_but_COLOR(bContext *C, uiBut *but, uiHandleButtonData *data, co
 #endif
     /* regular open menu */
     if (ELEM(event->type, LEFTMOUSE, EVT_PADENTER, EVT_RETKEY) && event->val == KM_PRESS) {
-      ui_palette_set_active(but);
+      ui_palette_set_active(color_but);
       button_activate_state(C, but, BUTTON_STATE_MENU_OPEN);
       return WM_UI_HANDLER_BREAK;
     }
@@ -5777,8 +5780,7 @@ static int ui_do_but_COLOR(bContext *C, uiBut *but, uiHandleButtonData *data, co
       ui_apply_but(C, but->block, but, data, true);
       return WM_UI_HANDLER_BREAK;
     }
-    if ((int)(but->a1) == UI_PALETTE_COLOR && event->type == EVT_DELKEY &&
-        event->val == KM_PRESS) {
+    if (color_but->is_pallete_color && (event->type == EVT_DELKEY) && (event->val == KM_PRESS)) {
       Palette *palette = (Palette *)but->rnapoin.owner_id;
       PaletteColor *color = but->rnapoin.data;
 
@@ -5809,7 +5811,7 @@ static int ui_do_but_COLOR(bContext *C, uiBut *but, uiHandleButtonData *data, co
     }
 
     if (event->type == LEFTMOUSE && event->val == KM_RELEASE) {
-      if ((int)(but->a1) == UI_PALETTE_COLOR) {
+      if (color_but->is_pallete_color) {
         if (!event->ctrl) {
           float color[3];
           Paint *paint = BKE_paint_get_active_from_context(C);
@@ -7613,13 +7615,7 @@ static int ui_do_button(bContext *C, uiBlock *block, uiBut *but, const wmEvent *
       retval = ui_do_but_BUT(C, but, data, event);
       break;
     case UI_BTYPE_COLOR:
-      if (but->a1 == -1) {
-        /* signal to prevent calling up color picker */
-        retval = ui_do_but_EXIT(C, but, data, event);
-      }
-      else {
-        retval = ui_do_but_COLOR(C, but, data, event);
-      }
+      retval = ui_do_but_COLOR(C, but, data, event);
       break;
     case UI_BTYPE_UNITVEC:
       retval = ui_do_but_UNITVEC(C, block, but, data, event);
diff --git a/source/blender/editors/interface/interface_intern.h b/source/blender/editors/interface/interface_intern.h
index 0dfa23a4332..9840444c0e0 100644
--- a/source/blender/editors/interface/interface_intern.h
+++ b/source/blender/editors/interface/interface_intern.h
@@ -177,7 +177,6 @@ struct uiBut {
    * - UI_BTYPE_LABEL:        Use `(a1 == 1.0f)` to use a2 as a blending factor (imaginative!).
    * - UI_BTYPE_SCROLL:       Use as scroll size.
    * - UI_BTYPE_SEARCH_MENU:  Use as number or rows.
-   * - UI_BTYPE_COLOR:        Use as indication of color palette.
    * - UI_BTYPE_PROGRESS_BAR: Use to store progress (0..1).
    */
   float a1;
@@ -188,7 +187,6 @@ struct uiBut {
    * - UI_BTYPE_NUM:          Use to store RNA 'precision' value, for dragging and click-step.
    * - UI_BTYPE_LABEL:        If `(a1 == 1.0f)` use a2 as a blending factor.
    * - UI_BTYPE_SEARCH_MENU:  Use as number or columns.
-   * - UI_BTYPE_COLOR:        Use as index in palette (not so good, needs refactor).
    */
   float a2;
 
@@ -281,6 +279,14 @@ struct uiBut {
   uiBlock *block;
 };
 
+/** Derived struct for #UI_BTYPE_COLOR */
+typedef struct uiButColor {
+  uiBut but;
+
+  bool is_pallete_color;
+  int palette_color_index;
+} uiButColor;
+
 /** Derived struct for #UI_BTYPE_TAB */
 typedef struct uiButTab {
   uiBut but;
diff --git a/source/blender/editors/interface/interface_templates.c b/source/blender/editors/interface/interface_templates.c
index 8c1d070b5e4..8593e7e3118 100644
--- a/source/blender/editors/interface/interface_templates.c
+++ b/source/blender/editors/interface/interface_templates.c
@@ -5512,22 +5512,24 @@ void uiTemplatePalette(uiLayout *layout,
     }
 
     RNA_pointer_create(&palette->id, &RNA_PaletteColor, color, &color_ptr);
-    uiDefButR(block,
-              UI_BTYPE_COLOR,
-              0,
-              "",
-              0,
-              0,
-              UI_UNIT_X,
-              UI_UNIT_Y,
-              &color_ptr,
-              "color",
-              -1,
-              0.0,
-              1.0,
-              UI_PALETTE_COLOR,
-              col_id,
-              "");
+    uiButColor *color_but = (uiButColor *)uiDefButR(block,
+                                                    UI_BTYPE_COLOR,
+                                                    0,
+                                                    "",
+                                                    0,
+                                                    0,
+                                                    UI_UNIT_X,
+                                                    UI_UNIT_Y,
+                                                    &color_ptr,
+                                                    "color",
+                                                    -1,
+                                                    0.0,
+                                                    1.0,
+                                                    0.0,
+                                                    0.0,
+                                                    "");
+    color_but->is_pallete_color = true;
+    color_but->palette_color_index = col_id;
     row_cols++;
     col_id++;
   }
diff --git a/source/blender/editors/interface/interface_utils.c b/source/blender/editors/interface/interface_utils.c
index 208fd7136da..4a1c7be918e 100644
--- a/source/blender/editors/interface/interface_utils.c
+++ b/source/blender/editors/interface/interface_utils.c
@@ -148,7 +148,7 @@ uiBut *uiDefAutoButR(uiBlock *block,
       if (RNA_property_array_check(prop) && index == -1) {
         if (ELEM(RNA_property_subtype(prop), PROP_COLOR, PROP_COLOR_GAMMA)) {
           but = uiDefButR_prop(
-              block, UI_BTYPE_COLOR, 0, name, x1, y1, x2, y2, ptr, prop, -1, 0, 0, -1, -1, NULL);
+              block, UI_BTYPE_COLOR, 0, name, x1, y1, x2, y2, ptr, prop, -1, 0, 0, 0, 0, NULL);
         }
         else {
           return NULL;
diff --git a/source/blender/editors/interface/interface_widgets.c b/source/blender/editors/interface/interface_widgets.c
index 01f89a8bdb1..5d342e928f9 100644
--- a/source/blender/editors/interface/interface_widgets.c
+++ b/source/blender/editors/interface/interface_widgets.c
@@ -3768,6 +3768,8 @@ static void widget_numslider(
 static void widget_swatch(
     uiBut *but, uiWidgetColors *wcol, rcti *rect, int state, int roundboxalign)
 {
+  BLI_assert(but->type == UI_BTYPE_COLOR);
+  uiButColor *color_but = (uiButColor *)but;
   uiWidgetBase wtb;
   float rad, col[4];
 
@@ -3822,8 +3824,8 @@ static void widget_swatch(
   }
 
   widgetbase_draw_ex(&wtb, wcol, show_alpha_checkers);
-  if (but->a1 == UI_PALETTE_COLOR &&
-      ((Palette *)but->rnapoin.owner_id)->active_color == (int)but->a2) {
+  if (color_but->is_pallete_color &&
+      ((Palette *)but->rnapoin.owner_id)->active_color == color_but->palette_color_index) {
     float width = rect->xmax - rect->xmin;
     float height = rect->ymax - rect->ymin;
     /* find color luminance and change it slightly */