[gtk/wip/chergert/popover-opaque-region: 1/3] native: add API to update opaque region

[Christian Hergert <chergert src gnome org>]

commit 8decf098bdbeb90c360d20e33321f96b41b30d64
Author: Christian Hergert <chergert redhat com>
Date:   Thu Feb 10 16:21:48 2022 -0800

    native: add API to update opaque region
    
    This abstracts the machinery to update the opaque region for a GtkWindow
    into GtkNative so it may be used from other native impelementations such
    as GtkPopover.
    
    Related #4689

 gtk/gtknative.c        | 154 ++++++++++++++++++++++++++++++++++++++++++++++++-
 gtk/gtknativeprivate.h |   5 ++
 2 files changed, 157 insertions(+), 2 deletions(-)
---
diff --git a/gtk/gtknative.c b/gtk/gtknative.c
index 0154781379..f65d65f55f 100644
--- a/gtk/gtknative.c
+++ b/gtk/gtknative.c
@@ -19,10 +19,15 @@
 
 #include "config.h"
 
-#include "gtknativeprivate.h"
-#include "gtkwidgetprivate.h"
 #include "gtkintl.h"
+
+#include "gtkcssboxesimplprivate.h"
+#include "gtkcsscolorvalueprivate.h"
+#include "gtkcsscornervalueprivate.h"
 #include "gtkcssnodeprivate.h"
+#include "gtkcssshadowvalueprivate.h"
+#include "gtknativeprivate.h"
+#include "gtkwidgetprivate.h"
 
 #include "gdk/gdksurfaceprivate.h"
 
@@ -297,3 +302,148 @@ gtk_native_queue_relayout (GtkNative *self)
   gdk_frame_clock_request_phase (clock, GDK_FRAME_CLOCK_PHASE_UPDATE);
   gdk_surface_request_layout (surface);
 }
+
+static void
+corner_rect (cairo_rectangle_int_t *rect,
+             const GtkCssValue     *value)
+{
+  rect->width = _gtk_css_corner_value_get_x (value, 100);
+  rect->height = _gtk_css_corner_value_get_y (value, 100);
+}
+
+static void
+subtract_decoration_corners_from_region (cairo_region_t        *region,
+                                         cairo_rectangle_int_t *extents,
+                                         GtkCssStyle           *style)
+{
+  cairo_rectangle_int_t rect;
+
+  corner_rect (&rect, style->border->border_top_left_radius);
+  rect.x = extents->x;
+  rect.y = extents->y;
+  cairo_region_subtract_rectangle (region, &rect);
+
+  corner_rect (&rect, style->border->border_top_right_radius);
+  rect.x = extents->x + extents->width - rect.width;
+  rect.y = extents->y;
+  cairo_region_subtract_rectangle (region, &rect);
+
+  corner_rect (&rect, style->border->border_bottom_left_radius);
+  rect.x = extents->x;
+  rect.y = extents->y + extents->height - rect.height;
+  cairo_region_subtract_rectangle (region, &rect);
+
+  corner_rect (&rect, style->border->border_bottom_right_radius);
+  rect.x = extents->x + extents->width - rect.width;
+  rect.y = extents->y + extents->height - rect.height;
+  cairo_region_subtract_rectangle (region, &rect);
+}
+
+static gboolean
+get_opaque_rect (GtkNative             *native,
+                 GtkCssStyle           *style,
+                 cairo_rectangle_int_t *rect)
+{
+  gboolean is_opaque;
+
+  g_assert (GTK_IS_NATIVE (native));
+  g_assert (_gtk_widget_get_realized (GTK_WIDGET (native)));
+  g_assert (style != NULL);
+  g_assert (rect != NULL);
+
+  is_opaque = gdk_rgba_is_opaque (gtk_css_color_value_get_rgba (style->background->background_color));
+
+  if (is_opaque && gtk_widget_get_opacity (GTK_WIDGET (native)) < 1.0)
+    is_opaque = FALSE;
+
+  if (is_opaque)
+    {
+      const graphene_rect_t *border_rect;
+      GtkCssBoxes css_boxes;
+      double native_x, native_y;
+
+      gtk_native_get_surface_transform (native, &native_x, &native_y);
+
+      gtk_css_boxes_init (&css_boxes, GTK_WIDGET (native));
+      border_rect = gtk_css_boxes_get_border_rect (&css_boxes);
+
+      rect->x = native_x + border_rect->origin.x;
+      rect->y = native_y + border_rect->origin.y;
+      rect->width = border_rect->size.width;
+      rect->height = border_rect->size.height;
+    }
+
+  return is_opaque;
+}
+
+static void
+get_shadow_width (GtkWidget *widget,
+                  GtkBorder *shadow_width,
+                  int        resize_handle_size)
+{
+  GtkCssNode *css_node = gtk_widget_get_css_node (widget);
+  GtkCssStyle *style = gtk_css_node_get_style (css_node);
+
+  gtk_css_shadow_value_get_extents (style->background->box_shadow, shadow_width);
+
+  shadow_width->left = MAX (shadow_width->left, resize_handle_size);
+  shadow_width->top = MAX (shadow_width->top, resize_handle_size);
+  shadow_width->bottom = MAX (shadow_width->bottom, resize_handle_size);
+  shadow_width->right = MAX (shadow_width->right, resize_handle_size);
+}
+
+void
+gtk_native_update_opaque_region (GtkNative  *native,
+                                 GtkWidget  *contents,
+                                 gboolean    subtract_decoration_corners,
+                                 gboolean    subtract_shadow,
+                                 int         resize_handle_size)
+{
+  cairo_rectangle_int_t rect;
+  cairo_region_t *opaque_region = NULL;
+  GtkCssStyle *style;
+  GtkCssNode *css_node;
+  GdkSurface *surface;
+  GtkBorder shadow;
+
+  g_return_if_fail (GTK_IS_NATIVE (native));
+  g_return_if_fail (!contents || GTK_IS_WIDGET (contents));
+
+  if (!_gtk_widget_get_realized (GTK_WIDGET (native)))
+    return;
+
+  if (contents != NULL)
+    css_node = gtk_widget_get_css_node (contents);
+  else
+    css_node = gtk_widget_get_css_node (GTK_WIDGET (native));
+
+  if (subtract_shadow)
+    get_shadow_width (GTK_WIDGET (native), &shadow, resize_handle_size);
+  else
+    shadow = (GtkBorder) {0, 0, 0, 0};
+
+  surface = gtk_native_get_surface (native);
+  style = gtk_css_node_get_style (css_node);
+
+  if (get_opaque_rect (native, style, &rect))
+    {
+      opaque_region = cairo_region_create_rectangle (&rect);
+
+      if (subtract_decoration_corners)
+        subtract_decoration_corners_from_region (opaque_region, &rect, style);
+
+      if (contents != NULL)
+        {
+          GtkAllocation alloc;
+
+          gtk_widget_get_allocation (contents, &alloc);
+
+          rect.x += alloc.x;
+          rect.y += alloc.y;
+        }
+    }
+
+  gdk_surface_set_opaque_region (surface, opaque_region);
+
+  cairo_region_destroy (opaque_region);
+}
diff --git a/gtk/gtknativeprivate.h b/gtk/gtknativeprivate.h
index 021402dcbf..d00ebc50cd 100644
--- a/gtk/gtknativeprivate.h
+++ b/gtk/gtknativeprivate.h
@@ -29,6 +29,11 @@ struct _GtkNativeInterface
 };
 
 void    gtk_native_queue_relayout         (GtkNative    *native);
+void    gtk_native_update_opaque_region   (GtkNative    *native,
+                                           GtkWidget    *contents,
+                                           gboolean      subtract_decoration_corners,
+                                           gboolean      subtract_shadow,
+                                           int           resize_handle_size);
 
 G_END_DECLS