Fix T92313: Heading of redo panel is not aligned properly

This corrects some alignments issues through new margins introduced in
93544b641bd6. Basic idea of this fix is to only add the new margins when
drawing a panel with background. These margins were added specifically
for the background boxes, so that makes sense.

Alternative fix to D13199.

This also fixes some margings added unintentionally in mentioned commit.
There is a little jump of the toolbar and the tabs in the Properties
when comparing the UI without this fix to 2.93:
{F12158085} {F12158039}
The jump is gone with this fix applied (compare to the 2.93 screenshot):
{F12158064}
While not a serious issue, this confirms that this fix actually tackles
the root of the issue.

2 files changed, 29 insertions, 17 deletions

diff --git a/source/blender/editors/interface/interface.c b/source/blender/editors/interface/interface.c
index 6ad0ef9de18..c5ccdbaac3b 100644
--- a/source/blender/editors/interface/interface.c
+++ b/source/blender/editors/interface/interface.c
@@ -2075,24 +2075,11 @@ void UI_block_draw(const bContext *C, uiBlock *block)
     ui_draw_menu_back(&style, block, &rect);
   }
   else if (block->panel) {
-    bool show_background = region->alignment != RGN_ALIGN_FLOAT;
-    if (show_background) {
-      if (block->panel->type && (block->panel->type->flag & PANEL_TYPE_NO_HEADER)) {
-        if (region->regiontype == RGN_TYPE_TOOLS) {
-          /* We never want a background around active tools. */
-          show_background = false;
-        }
-        else {
-          /* Without a header there is no background except for region overlap. */
-          show_background = region->overlap != 0;
-        }
-      }
-    }
     ui_draw_aligned_panel(&style,
                           block,
                           &rect,
                           UI_panel_category_is_visible(region),
-                          show_background,
+                          UI_panel_should_show_background(region, block->panel->type),
                           region->flag & RGN_FLAG_SEARCH_FILTER_ACTIVE);
   }
 
diff --git a/source/blender/editors/interface/interface_panel.c b/source/blender/editors/interface/interface_panel.c
index 6aa4c5bb4a7..d1daf5b48bf 100644
--- a/source/blender/editors/interface/interface_panel.c
+++ b/source/blender/editors/interface/interface_panel.c
@@ -1334,6 +1334,26 @@ void ui_draw_aligned_panel(const uiStyle *style,
   }
 }
 
+bool UI_panel_should_show_background(const ARegion *region, const PanelType *panel_type)
+{
+  if (region->alignment == RGN_ALIGN_FLOAT) {
+    return false;
+  }
+
+  if (panel_type && panel_type->flag & PANEL_TYPE_NO_HEADER) {
+    if (region->regiontype == RGN_TYPE_TOOLS) {
+      /* We never want a background around active tools. */
+      return false;
+    }
+    else {
+      /* Without a header there is no background except for region overlap. */
+      return region->overlap != 0;
+    }
+  }
+
+  return true;
+}
+
 /** \} */
 
 /* -------------------------------------------------------------------- */
@@ -1746,17 +1766,22 @@ static bool uiAlignPanelStep(ARegion *region, const float factor, const bool dra
   const int region_offset_x = panel_region_offset_x_get(region);
   for (int i = 0; i < active_panels_len; i++) {
     PanelSort *ps = &panel_sort[i];
-    const bool no_header = ps->panel->type->flag & PANEL_TYPE_NO_HEADER;
+    const bool show_background = UI_panel_should_show_background(region, ps->panel->type);
     ps->panel->runtime.region_ofsx = region_offset_x;
-    ps->new_offset_x = region_offset_x + (no_header ? 0 : UI_PANEL_MARGIN_X);
+    ps->new_offset_x = region_offset_x + (show_background ? UI_PANEL_MARGIN_X : 0);
   }
 
   /* Y offset. */
   for (int i = 0, y = 0; i < active_panels_len; i++) {
     PanelSort *ps = &panel_sort[i];
+    const bool show_background = UI_panel_should_show_background(region, ps->panel->type);
+
     y -= get_panel_real_size_y(ps->panel);
 
-    y -= UI_PANEL_MARGIN_Y;
+    /* Separate panel boxes a bit further (if they are drawn). */
+    if (show_background) {
+      y -= UI_PANEL_MARGIN_Y;
+    }
     ps->new_offset_y = y;
     /* The header still draws offset by the size of closed panels, so apply the offset here. */
     if (UI_panel_is_closed(ps->panel)) {