let the ui layer (via the core) construct the frame mask

Based on mutter commit:
https://git.gnome.org/browse/mutter/commit/?id=c2a9ccb7e2e0f7dc37866099a5e5a4a5727c679b

3 files changed, 115 insertions, 35 deletions

diff --git a/src/ui/frames.c b/src/ui/frames.c
index 5691d242..c6e636dd 100644
--- a/src/ui/frames.c
+++ b/src/ui/frames.c
@@ -40,6 +40,10 @@
 
 #define DEFAULT_INNER_BUTTON_BORDER 3
 
+#ifndef M_PI
+#define M_PI 3.14159265358979323846264338327
+#endif
+
 static void meta_frames_destroy       (GtkWidget *widget);
 static void meta_frames_finalize      (GObject   *object);
 static void meta_frames_style_updated (GtkWidget *widget);
@@ -841,22 +845,6 @@ meta_ui_frame_get_corner_radiuses (MetaFrames  *frames,
     *bottom_right = fgeom.bottom_right_corner_rounded_radius + sqrt(fgeom.bottom_right_corner_rounded_radius);
 }
 
-void
-meta_frames_get_corner_radiuses (MetaFrames *frames,
-                                 Window      xwindow,
-                                 float      *top_left,
-                                 float      *top_right,
-                                 float      *bottom_left,
-                                 float      *bottom_right)
-{
-  MetaUIFrame *frame;
-
-  frame = meta_frames_lookup_window (frames, xwindow);
-
-  meta_ui_frame_get_corner_radiuses (frames, frame, top_left, top_right,
-                                     bottom_left, bottom_right);
-}
-
 static void
 apply_cairo_region_to_window (Display        *display,
                               Window          xwindow,
@@ -2461,6 +2449,102 @@ find_frame_to_draw (MetaFrames *frames,
   return NULL;
 }
 
+#define TAU (2*M_PI)
+
+/*
+ * Draw the opaque and semi-opaque pixels of this frame into a mask.
+ *
+ * (0,0) in Cairo coordinates is assumed to be the top left corner of the
+ * invisible border.
+ *
+ * The parts of @cr's surface in the clip region are assumed to be
+ * initialized to fully-transparent, and the clip region is assumed to
+ * contain the invisible border and the visible parts of the frame, but
+ * not the client area.
+ *
+ * This function uses @cr to draw pixels of arbitrary color (it will
+ * typically be drawing in a %CAIRO_FORMAT_A8 surface, so the color is
+ * discarded anyway) with appropriate alpha values to reproduce this
+ * frame's alpha channel, as a mask to be applied to an opaque pixmap.
+ *
+ * @frame: This frame
+ * @xwindow: The X window for the frame, which has the client window as a child
+ * @width: The width of the framed window including any invisible borders
+ * @height: The height of the framed window including any invisible borders
+ * @cr: Used to draw the resulting mask
+ */
+void
+meta_frames_get_mask (MetaFrames          *frames,
+                      Window               xwindow,
+                      guint                width,
+                      guint                height,
+                      cairo_t             *cr)
+{
+  MetaUIFrame *frame = meta_frames_lookup_window (frames, xwindow);
+  float top_left, top_right, bottom_left, bottom_right;
+  int x, y;
+  MetaFrameBorders borders;
+
+  if (frame == NULL)
+    meta_bug ("No such frame 0x%lx\n", xwindow);
+
+  cairo_save (cr);
+
+  meta_ui_frame_get_borders (frames, frame, &borders);
+  meta_ui_frame_get_corner_radiuses (frames, frame,
+                                     &top_left, &top_right,
+                                     &bottom_left, &bottom_right);
+
+  /* top left */
+  x = borders.invisible.left;
+  y = borders.invisible.top;
+
+  cairo_arc (cr,
+             x + top_left,
+             y + top_left,
+             top_left,
+             2 * TAU / 4,
+             3 * TAU / 4);
+
+  /* top right */
+  x = width - borders.invisible.right - top_right;
+  y = borders.invisible.top;
+
+  cairo_arc (cr,
+             x,
+             y + top_right,
+             top_right,
+             3 * TAU / 4,
+             4 * TAU / 4);
+
+  /* bottom right */
+  x = width - borders.invisible.right - bottom_right;
+  y = height - borders.invisible.bottom - bottom_right;
+
+  cairo_arc (cr,
+             x,
+             y,
+             bottom_right,
+             0 * TAU / 4,
+             1 * TAU / 4);
+
+  /* bottom left */
+  x = borders.invisible.left;
+  y = height - borders.invisible.bottom - bottom_left;
+
+  cairo_arc (cr,
+             x + bottom_left,
+             y,
+             bottom_left,
+             1 * TAU / 4,
+             2 * TAU / 4);
+
+  cairo_set_source_rgba (cr, 1, 1, 1, 1);
+  cairo_fill (cr);
+
+  cairo_restore (cr);
+}
+
 static gboolean
 meta_frames_draw (GtkWidget *widget,
                   cairo_t   *cr)
diff --git a/src/ui/frames.h b/src/ui/frames.h
index dcce7a44..568a9643 100644
--- a/src/ui/frames.h
+++ b/src/ui/frames.h
@@ -146,12 +146,11 @@ cairo_region_t *meta_frames_get_frame_bounds (MetaFrames *frames,
                                               int         window_width,
                                               int         window_height);
 
-void meta_frames_get_corner_radiuses (MetaFrames *frames,
-                                      Window      xwindow,
-                                      float      *top_left,
-                                      float      *top_right,
-                                      float      *bottom_left,
-                                      float      *bottom_right);
+void meta_frames_get_mask (MetaFrames *frames,
+                           Window      xwindow,
+                           guint       width,
+                           guint       height,
+                           cairo_t    *cr);
 
 void meta_frames_move_resize_frame (MetaFrames *frames,
 				    Window      xwindow,
diff --git a/src/ui/ui.c b/src/ui/ui.c
index ccde3f5f..239c63f0 100644
--- a/src/ui/ui.c
+++ b/src/ui/ui.c
@@ -304,6 +304,16 @@ meta_ui_free (MetaUI *ui)
 }
 
 void
+meta_ui_get_frame_mask (MetaUI  *ui,
+                        Window   frame_xwindow,
+                        guint    width,
+                        guint    height,
+                        cairo_t *cr)
+{
+  meta_frames_get_mask (ui->frames, frame_xwindow, width, height, cr);
+}
+
+void
 meta_ui_get_frame_borders (MetaUI *ui,
                            Window frame_xwindow,
                            MetaFrameBorders *borders)
@@ -311,19 +321,6 @@ meta_ui_get_frame_borders (MetaUI *ui,
   meta_frames_get_borders (ui->frames, frame_xwindow, borders);
 }
 
-void
-meta_ui_get_corner_radiuses (MetaUI *ui,
-                             Window  xwindow,
-                             float  *top_left,
-                             float  *top_right,
-                             float  *bottom_left,
-                             float  *bottom_right)
-{
-  meta_frames_get_corner_radiuses (ui->frames, xwindow,
-                                   top_left, top_right,
-                                   bottom_left, bottom_right);
-}
-
 static void
 set_background_none (Display *xdisplay,
                      Window   xwindow)