From 840c50b00d2f7d8a8f9620872eae1ecbb81e1f3f Mon Sep 17 00:00:00 2001
From: Olivier Fourdan <ofourdan@redhat.com>
Date: Tue, 4 Feb 2020 14:58:30 +0100
Subject: [PATCH] window-actor: Ensure clipping in `capture_into()`

The clip bounds passed in `meta_window_actor_capture_into()` represent
the actual allocated buffer size where the window actor image will be
eventually copied.

As such, it is completely agnostic to the scaling factors that might
affect the different surface actors which compose the window actor.

So instead of trying to compute the scale factor by which the given
clipping bounds need to be adjusted, simply clip the resulting image
based on the given bounds to make sure we never overflow the destination
buffer.

https://gitlab.gnome.org/GNOME/mutter/merge_requests/1022
---
 src/compositor/meta-window-actor.c | 24 ++++++++++++++----------
 1 file changed, 14 insertions(+), 10 deletions(-)

diff --git a/src/compositor/meta-window-actor.c b/src/compositor/meta-window-actor.c
index 9f4568662..8ce6bc609 100644
--- a/src/compositor/meta-window-actor.c
+++ b/src/compositor/meta-window-actor.c
@@ -1259,32 +1259,36 @@ meta_window_actor_capture_into (MetaScreenCastWindow *screen_cast_window,
   cr_height = cairo_image_surface_get_height (image);
   cr_stride = cairo_image_surface_get_stride (image);
 
-  if (cr_width < bounds->width || cr_height < bounds->height)
+  if (cr_width == bounds->width && cr_height == bounds->height)
     {
+      memcpy (data, cr_data, cr_height * cr_stride);
+    }
+  else
+    {
+      int width = MIN (bounds->width, cr_width);
+      int height = MIN (bounds->height, cr_height);
+      int stride = width * bpp;
       uint8_t *src, *dst;
+
       src = cr_data;
       dst = data;
 
-      for (int i = 0; i < cr_height; i++)
+      for (int i = 0; i < height; i++)
         {
-          memcpy (dst, src, cr_stride);
-          if (cr_width < bounds->width)
-            memset (dst + cr_stride, 0, (bounds->width * bpp) - cr_stride);
+          memcpy (dst, src, stride);
+          if (width < bounds->width)
+            memset (dst + stride, 0, (bounds->width * bpp) - stride);
 
           src += cr_stride;
           dst += bounds->width * bpp;
         }
 
-      for (int i = cr_height; i < bounds->height; i++)
+      for (int i = height; i < bounds->height; i++)
         {
           memset (dst, 0, bounds->width * bpp);
           dst += bounds->width * bpp;
         }
     }
-  else
-    {
-      memcpy (data, cr_data, cr_height * cr_stride);
-    }
 
   cairo_surface_destroy (image);
 }