[mutter] clutter/stage: Make paint_to_buffer use the correct texture/buffer size

[Jonas Ådahl <jadahl src gnome org>]

commit e216d9c6ad377ba5ed51d0edf9805ca7c73a7e63
Author: Sebastian Keller <skeller gnome org>
Date:   Wed Jun 17 15:32:54 2020 +0200

    clutter/stage: Make paint_to_buffer use the correct texture/buffer size
    
    The size of the buffer the texture will be written to by
    paint_to_buffer() is determined based on
    meta_screen_cast_area_stream_src_get_specs() which uses roundf() to
    calculate the width and height after scaling. Because the size of the
    texture to be written to that buffer is calculated using ceilf(), it
    might exceed the allocated buffer when using fractional scaling.
    
    In 3.36 paint_to_buffer() is used from capture_view() which also uses
    roundf() to allocate its buffer. Here this leads to a memory corruption
    resulting in a crash when taking screenshots of an area.
    
    Fixes https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/2842
    
    https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1320

 clutter/clutter/clutter-stage.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/clutter/clutter/clutter-stage.c b/clutter/clutter/clutter-stage.c
index 04ad08eb3b..1567bf0937 100644
--- a/clutter/clutter/clutter-stage.c
+++ b/clutter/clutter/clutter-stage.c
@@ -4176,8 +4176,8 @@ clutter_stage_paint_to_buffer (ClutterStage                 *stage,
   CoglFramebuffer *framebuffer;
   CoglBitmap *bitmap;
 
-  texture_width = (int) ceilf (rect->width * scale);
-  texture_height = (int) ceilf (rect->height * scale);
+  texture_width = (int) roundf (rect->width * scale);
+  texture_height = (int) roundf (rect->height * scale);
   texture = cogl_texture_2d_new_with_size (cogl_context,
                                            texture_width,
                                            texture_height);