UI: Visual style update to panels

Back in Blender 2.30, the GUI project brought panels into Blender among other important visual updates.
For the first time it was possible to move the wall of buttons around. Providing a clear separation
between sections (it even allowed the grouping of panels in tabs!)

During the 2.5 redesign, the separation between panels became a line on top of each panel, and panels received
theme settings for background and header colors. The default theme used the same color for both.

In 2.8 the background color of panels was different from headers in the default theme, so the separator
line was removed. While the separator line wasn't elegant (only on top, non-themeable, hard-coded emboss effect),
it provided a sort of separation between panels.

This patch solves the panels-separation by simply adding a margin space around them (not visible in default theme yet).
Even though the margin reduces the width of the working area slightly, it makes room for the upcoming always-visible scrollbars.

Other adjustments:
* Use arrow icon instead of triangle to collapse/expand
* Use rounded corners to match the rest of the UI (editor corners, nodes, etc).

{F10953929, size=full}

Margin on panels makes use of the `style->panelouter` property that hasn't been
used in a while. Also slight tweaks to `boxspace` and `templatespace` style properties so they
are multiples of 2 and operations on them round better.

There is technically no need to update the themes for them to work, so no theme changes are included in this patch.

{F10953931, size=full}

{F10953933, size=full}

{F10953934, size=full}

{F10954003, size=full}

----

A new theme setting under Style controls the roundness of all panels (added it to Style instead of ThemeSpace because I think controlling the panel roundness per editor is a bit overkill):
{F11091561, size=full, autoplay, loop}

Reviewed By: HooglyBoogly

Differential Revision: https://developer.blender.org/D12814

6 files changed, 72 insertions, 124 deletions

diff --git a/source/blender/editors/animation/fmodifier_ui.c b/source/blender/editors/animation/fmodifier_ui.c
index 40871fba2be..cea0e50a21f 100644
--- a/source/blender/editors/animation/fmodifier_ui.c
+++ b/source/blender/editors/animation/fmodifier_ui.c
@@ -187,7 +187,7 @@ static PanelType *fmodifier_panel_register(ARegionType *region_type,
 
   /* Give the panel the special flag that says it was built here and corresponds to a
    * modifier rather than a #PanelType. */
-  panel_type->flag = PANEL_TYPE_HEADER_EXPAND | PANEL_TYPE_DRAW_BOX | PANEL_TYPE_INSTANCED;
+  panel_type->flag = PANEL_TYPE_HEADER_EXPAND  | PANEL_TYPE_INSTANCED;
   panel_type->reorder = fmodifier_reorder;
   panel_type->get_list_data_expand_flag = get_fmodifier_expand_flag;
   panel_type->set_list_data_expand_flag = set_fmodifier_expand_flag;
@@ -221,7 +221,7 @@ static PanelType *fmodifier_subpanel_register(ARegionType *region_type,
   panel_type->draw_header = draw_header;
   panel_type->draw = draw;
   panel_type->poll = poll;
-  panel_type->flag = PANEL_TYPE_DEFAULT_CLOSED | PANEL_TYPE_DRAW_BOX;
+  panel_type->flag = PANEL_TYPE_DEFAULT_CLOSED ;
 
   BLI_assert(parent != NULL);
   BLI_strncpy(panel_type->parent_id, parent->idname, BKE_ST_MAXNAME);
diff --git a/source/blender/editors/include/UI_interface.h b/source/blender/editors/include/UI_interface.h
index ddd5e77cbb6..c808a42a44a 100644
--- a/source/blender/editors/include/UI_interface.h
+++ b/source/blender/editors/include/UI_interface.h
@@ -252,7 +252,8 @@ enum {
 
 #define UI_PANEL_CATEGORY_MARGIN_WIDTH (U.widget_unit * 1.0f)
 
-#define UI_PANEL_BOX_STYLE_MARGIN (U.widget_unit * 0.2f)
+#define UI_PANEL_MARGIN_X (U.widget_unit * 0.4f)
+#define UI_PANEL_MARGIN_Y (U.widget_unit * 0.2f)
 
 /* but->drawflag - these flags should only affect how the button is drawn. */
 /* NOTE: currently, these flags *are not passed* to the widget's state() or draw() functions
diff --git a/source/blender/editors/interface/interface_intern.h b/source/blender/editors/interface/interface_intern.h
index c7781d65058..0301ab9156e 100644
--- a/source/blender/editors/interface/interface_intern.h
+++ b/source/blender/editors/interface/interface_intern.h
@@ -116,7 +116,7 @@ extern const char ui_radial_dir_to_numpad[8];
 extern const short ui_radial_dir_to_angle[8];
 
 /* internal panel drawing defines */
-#define PNL_HEADER (UI_UNIT_Y * 1.2) /* 24 default */
+#define PNL_HEADER (UI_UNIT_Y * 1.25) /* 24 default */
 
 /* bit button defines */
 /* Bit operations */
diff --git a/source/blender/editors/interface/interface_panel.c b/source/blender/editors/interface/interface_panel.c
index a64797af24f..e5f84f63d35 100644
--- a/source/blender/editors/interface/interface_panel.c
+++ b/source/blender/editors/interface/interface_panel.c
@@ -1112,23 +1112,14 @@ static void panel_draw_highlight_border(const Panel *panel,
                                         const rcti *rect,
                                         const rcti *header_rect)
 {
-  const bool draw_box_style = panel->type->flag & PANEL_TYPE_DRAW_BOX;
   const bool is_subpanel = panel->type->parent != NULL;
   if (is_subpanel) {
     return;
   }
 
-  float radius;
-  if (draw_box_style) {
-    /* Use the theme for box widgets. */
-    const uiWidgetColors *box_wcol = &UI_GetTheme()->tui.wcol_box;
-    UI_draw_roundbox_corner_set(UI_CNR_ALL);
-    radius = box_wcol->roundness * U.widget_unit;
-  }
-  else {
-    UI_draw_roundbox_corner_set(UI_CNR_NONE);
-    radius = 0.0f;
-  }
+  const bTheme *btheme = UI_GetTheme();
+  const float radius = btheme->tui.panel_roundness * U.widget_unit * 0.5f;
+  UI_draw_roundbox_corner_set(UI_CNR_ALL);
 
   float color[4];
   UI_GetThemeColor4fv(TH_SELECT_ACTIVE, color);
@@ -1172,18 +1163,17 @@ static void panel_draw_aligned_widgets(const uiStyle *style,
 
   /* Draw collapse icon. */
   {
-    rctf collapse_rect = {
-        .xmin = widget_rect.xmin,
-        .xmax = widget_rect.xmin + header_height,
-        .ymin = widget_rect.ymin,
-        .ymax = widget_rect.ymax,
-    };
-    BLI_rctf_scale(&collapse_rect, 0.25f);
-
-    float triangle_color[4];
-    rgba_uchar_to_float(triangle_color, title_color);
-
-    ui_draw_anti_tria_rect(&collapse_rect, UI_panel_is_closed(panel) ? 'h' : 'v', triangle_color);
+    const float size_y = BLI_rcti_size_y(&widget_rect);
+    GPU_blend(GPU_BLEND_ALPHA);
+    UI_icon_draw_ex(widget_rect.xmin + size_y * 0.2f,
+                    widget_rect.ymin + size_y * 0.2f,
+                    UI_panel_is_closed(panel) ? ICON_RIGHTARROW : ICON_DOWNARROW_HLT,
+                    aspect * U.inv_dpi_fac,
+                    0.7f,
+                    0.0f,
+                    title_color,
+                    false);
+    GPU_blend(GPU_BLEND_NONE);
   }
 
   /* Draw text label. */
@@ -1243,7 +1233,6 @@ static void panel_draw_aligned_backdrop(const Panel *panel,
                                         const rcti *rect,
                                         const rcti *header_rect)
 {
-  const bool draw_box_style = panel->type->flag & PANEL_TYPE_DRAW_BOX;
   const bool is_subpanel = panel->type->parent != NULL;
   const bool is_open = !UI_panel_is_closed(panel);
 
@@ -1251,90 +1240,52 @@ static void panel_draw_aligned_backdrop(const Panel *panel,
     return;
   }
 
-  const uint pos = GPU_vertformat_attr_add(
-      immVertexFormat(), "pos", GPU_COMP_F32, 2, GPU_FETCH_FLOAT);
+  const bTheme *btheme = UI_GetTheme();
+  const float radius = btheme->tui.panel_roundness * U.widget_unit * 0.5f;
 
-  /* Draw with an opaque box backdrop for box style panels. */
-  if (draw_box_style) {
-    /* Use the theme for box widgets. */
-    const uiWidgetColors *box_wcol = &UI_GetTheme()->tui.wcol_box;
-
-    if (is_subpanel) {
-      /* Use rounded bottom corners for the last subpanel. */
-      if (panel->next == NULL) {
-        UI_draw_roundbox_corner_set(UI_CNR_BOTTOM_RIGHT | UI_CNR_BOTTOM_LEFT);
-        float color[4];
-        UI_GetThemeColor4fv(TH_PANEL_SUB_BACK, color);
-        /* Change the width a little bit to line up with sides. */
-        UI_draw_roundbox_aa(
-            &(const rctf){
-                .xmin = rect->xmin + U.pixelsize,
-                .xmax = rect->xmax - U.pixelsize,
-                .ymin = rect->ymin + U.pixelsize,
-                .ymax = rect->ymax,
-            },
-            true,
-            box_wcol->roundness * U.widget_unit,
-            color);
-      }
-      else {
-        immBindBuiltinProgram(GPU_SHADER_2D_UNIFORM_COLOR);
-        immUniformThemeColor(TH_PANEL_SUB_BACK);
-        immRectf(pos, rect->xmin + U.pixelsize, rect->ymin, rect->xmax - U.pixelsize, rect->ymax);
-        immUnbindProgram();
-      }
-    }
-    else {
-      /* Expand the top a tiny bit to give header buttons equal size above and below. */
-      rcti box_rect = {
-          .xmin = rect->xmin,
-          .xmax = rect->xmax,
-          .ymin = is_open ? rect->ymin : header_rect->ymin,
-          .ymax = header_rect->ymax + U.pixelsize,
-      };
-      ui_draw_box_opaque(&box_rect, UI_CNR_ALL);
-
-      /* Mimic the border between aligned box widgets for the bottom of the header. */
-      if (is_open) {
-        immBindBuiltinProgram(GPU_SHADER_2D_UNIFORM_COLOR);
-        GPU_blend(GPU_BLEND_ALPHA);
-
-        /* Top line. */
-        immUniformColor4ubv(box_wcol->outline);
-        immRectf(pos, rect->xmin, header_rect->ymin - U.pixelsize, rect->xmax, header_rect->ymin);
-
-        /* Bottom "shadow" line. */
-        immUniformThemeColor(TH_WIDGET_EMBOSS);
-        immRectf(pos,
-                 rect->xmin,
-                 header_rect->ymin - U.pixelsize,
-                 rect->xmax,
-                 header_rect->ymin - U.pixelsize - 1);
-
-        GPU_blend(GPU_BLEND_NONE);
-        immUnbindProgram();
-      }
-    }
-  }
-  else {
-    immBindBuiltinProgram(GPU_SHADER_2D_UNIFORM_COLOR);
-    GPU_blend(GPU_BLEND_ALPHA);
-
-    /* Panel backdrop. */
-    if (is_open || panel->type->flag & PANEL_TYPE_NO_HEADER) {
-      immUniformThemeColor(is_subpanel ? TH_PANEL_SUB_BACK : TH_PANEL_BACK);
-      immRectf(pos, rect->xmin, rect->ymin, rect->xmax, rect->ymax);
-    }
-
-    /* Panel header backdrops for non sub-panels. */
-    if (!is_subpanel) {
-      immUniformThemeColor(UI_panel_matches_search_filter(panel) ? TH_MATCH : TH_PANEL_HEADER);
-      immRectf(pos, rect->xmin, header_rect->ymin, rect->xmax, header_rect->ymax);
-    }
-
-    GPU_blend(GPU_BLEND_NONE);
-    immUnbindProgram();
-  }
+  immBindBuiltinProgram(GPU_SHADER_2D_UNIFORM_COLOR);
+  GPU_blend(GPU_BLEND_ALPHA);
+
+  /* Panel backdrop. */
+  if (is_open || panel->type->flag & PANEL_TYPE_NO_HEADER) {
+    float panel_backcolor[4];
+    UI_draw_roundbox_corner_set(is_open ? UI_CNR_BOTTOM_RIGHT | UI_CNR_BOTTOM_LEFT : UI_CNR_ALL);
+    UI_GetThemeColor4fv((is_subpanel ? TH_PANEL_SUB_BACK : TH_PANEL_BACK), panel_backcolor);
+
+    UI_draw_roundbox_4fv(
+        &(const rctf){
+            .xmin = rect->xmin,
+            .xmax = rect->xmax,
+            .ymin = rect->ymin,
+            .ymax = rect->ymax,
+        },
+        true,
+        radius,
+        panel_backcolor);
+  }
+
+  /* Panel header backdrops for non sub-panels. */
+  if (!is_subpanel) {
+    float panel_headercolor[4];
+    UI_GetThemeColor4fv(UI_panel_matches_search_filter(panel) ? TH_MATCH : TH_PANEL_HEADER,
+                        panel_headercolor);
+    UI_draw_roundbox_corner_set(is_open ? UI_CNR_TOP_RIGHT | UI_CNR_TOP_LEFT : UI_CNR_ALL);
+
+    /* Change the width a little bit to line up with the sides. */
+    UI_draw_roundbox_4fv(
+        &(const rctf){
+            .xmin = rect->xmin,
+            .xmax = rect->xmax,
+            .ymin = header_rect->ymin,
+            .ymax = header_rect->ymax,
+        },
+        true,
+        radius,
+        panel_headercolor);
+  }
+
+  GPU_blend(GPU_BLEND_NONE);
+  immUnbindProgram();
 }
 
 /**
@@ -1789,9 +1740,9 @@ 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 use_box = ps->panel->type->flag & PANEL_TYPE_DRAW_BOX;
+    const bool no_header = ps->panel->type->flag & PANEL_TYPE_NO_HEADER;
     ps->panel->runtime.region_ofsx = region_offset_x;
-    ps->new_offset_x = region_offset_x + ((use_box) ? UI_PANEL_BOX_STYLE_MARGIN : 0);
+    ps->new_offset_x = region_offset_x + (no_header ? 0 : UI_PANEL_MARGIN_X);
   }
 
   /* Y offset. */
@@ -1799,10 +1750,7 @@ static bool uiAlignPanelStep(ARegion *region, const float factor, const bool dra
     PanelSort *ps = &panel_sort[i];
     y -= get_panel_real_size_y(ps->panel);
 
-    const bool use_box = ps->panel->type->flag & PANEL_TYPE_DRAW_BOX;
-    if (use_box) {
-      y -= UI_PANEL_BOX_STYLE_MARGIN;
-    }
+    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)) {
diff --git a/source/blender/editors/screen/area.c b/source/blender/editors/screen/area.c
index 473674f1059..406f5c0904f 100644
--- a/source/blender/editors/screen/area.c
+++ b/source/blender/editors/screen/area.c
@@ -2977,12 +2977,11 @@ void ED_region_panels_layout_ex(const bContext *C,
     margin_x = category_tabs_width;
   }
 
-  const int w = BLI_rctf_size_x(&v2d->cur) - margin_x;
+  const int width_no_header = BLI_rctf_size_x(&v2d->cur) - margin_x;
+  const int width = width_no_header - UI_PANEL_MARGIN_X * 2.0f;
   /* Works out to 10 * UI_UNIT_X or 20 * UI_UNIT_X. */
   const int em = (region->type->prefsizex) ? 10 : 20;
 
-  const int w_box_panel = w - UI_PANEL_BOX_STYLE_MARGIN * 2.0f;
-
   /* create panels */
   UI_panels_begin(C, region);
 
@@ -3018,7 +3017,7 @@ void ED_region_panels_layout_ex(const bContext *C,
                   &region->panels,
                   pt,
                   panel,
-                  (pt->flag & PANEL_TYPE_DRAW_BOX) ? w_box_panel : w,
+                  (pt->flag & PANEL_TYPE_NO_HEADER) ? width_no_header : width,
                   em,
                   NULL,
                   search_filter);
@@ -3052,7 +3051,7 @@ void ED_region_panels_layout_ex(const bContext *C,
                     &region->panels,
                     panel->type,
                     panel,
-                    (panel->type->flag & PANEL_TYPE_DRAW_BOX) ? w_box_panel : w,
+                    (panel->type->flag & PANEL_TYPE_NO_HEADER) ? width_no_header : width,
                     em,
                     unique_panel_str,
                     search_filter);
diff --git a/source/blender/editors/space_spreadsheet/spreadsheet_row_filter_ui.cc b/source/blender/editors/space_spreadsheet/spreadsheet_row_filter_ui.cc
index 219d03c1dcd..78804172981 100644
--- a/source/blender/editors/space_spreadsheet/spreadsheet_row_filter_ui.cc
+++ b/source/blender/editors/space_spreadsheet/spreadsheet_row_filter_ui.cc
@@ -336,7 +336,7 @@ void register_row_filter_panels(ARegionType &region_type)
     strcpy(panel_type->label, "");
     strcpy(panel_type->category, "Filters");
     strcpy(panel_type->translation_context, BLT_I18NCONTEXT_DEFAULT_BPYRNA);
-    panel_type->flag = PANEL_TYPE_INSTANCED | PANEL_TYPE_DRAW_BOX | PANEL_TYPE_HEADER_EXPAND;
+    panel_type->flag = PANEL_TYPE_INSTANCED  | PANEL_TYPE_HEADER_EXPAND;
     panel_type->draw_header = spreadsheet_filter_panel_draw_header;
     panel_type->draw = spreadsheet_filter_panel_draw;
     panel_type->get_list_data_expand_flag = get_filter_expand_flag;