[gnome-shell] blur-effect: Don't use stage view when drawing off-stage

[Marge Bot <marge-bot src gnome org>]

commit 09602ae2aee963710bd1cbbf7102fc1632d4e0df
Author: Jonas Dreßler <verdre v0yd nl>
Date:   Sat Feb 13 16:07:22 2021 +0100

    blur-effect: Don't use stage view when drawing off-stage
    
    When we're painting off-stage, for example because we're screencasting
    or taking a screenshot, there won't be a stage-view associated with the
    paint context. The BlurEffect previously didn't handle that case and
    would crash.
    
    Fix that and handle that case by assuming the scale is 1 and not
    offsetting the rectangle we blit from the draw framebuffer.
    
    Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1673>

 src/shell-blur-effect.c | 21 ++++++++++++++++-----
 1 file changed, 16 insertions(+), 5 deletions(-)
---
diff --git a/src/shell-blur-effect.c b/src/shell-blur-effect.c
index 16bf086de6..8ea333f0cf 100644
--- a/src/shell-blur-effect.c
+++ b/src/shell-blur-effect.c
@@ -327,7 +327,6 @@ update_actor_box (ShellBlurEffect     *self,
   float box_scale_factor = 1.0f;
   float origin_x, origin_y;
   float width, height;
-  cairo_rectangle_int_t stage_view_layout;
 
   switch (self->mode)
     {
@@ -337,14 +336,26 @@ update_actor_box (ShellBlurEffect     *self,
 
     case SHELL_BLUR_MODE_BACKGROUND:
       stage_view = clutter_paint_context_get_stage_view (paint_context);
-      box_scale_factor = clutter_stage_view_get_scale (stage_view);
-      clutter_stage_view_get_layout (stage_view, &stage_view_layout);
 
       clutter_actor_get_transformed_position (self->actor, &origin_x, &origin_y);
       clutter_actor_get_transformed_size (self->actor, &width, &height);
 
-      origin_x -= stage_view_layout.x;
-      origin_y -= stage_view_layout.y;
+      if (stage_view)
+        {
+          cairo_rectangle_int_t stage_view_layout;
+
+          box_scale_factor = clutter_stage_view_get_scale (stage_view);
+          clutter_stage_view_get_layout (stage_view, &stage_view_layout);
+
+          origin_x -= stage_view_layout.x;
+          origin_y -= stage_view_layout.y;
+        }
+      else
+        {
+          /* If we're drawing off stage, just assume scale = 1, this won't work
+           * with stage-view scaling though.
+           */
+        }
 
       clutter_actor_box_set_origin (source_actor_box, origin_x, origin_y);
       clutter_actor_box_set_size (source_actor_box, width, height);