[mutter] clutter/stage: Round viewport coordinates before setting

[Jonas Ådahl <jadahl src gnome org>]

commit 4baefe46b30fcc9b22849a5ccab0622d04fbe451
Author: Jonas Ådahl <jadahl gmail com>
Date:   Fri Oct 27 04:37:46 2017 -0500

    clutter/stage: Round viewport coordinates before setting
    
    cogl_(fromebuffer)_set_viewport will implicitly cast away the fraction
    of a floating point number, meaning if a coordinate calculation
    resulted in just below the integer (which for example ~1.75 scaling on
    a 1920x1080 did), we'd set a one pixel too narrow viewport. Fix this by
    always rounding the floating point to the closest int before passing,
    avoiding the precision loss.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=765011

 clutter/clutter/clutter-stage.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)
---
diff --git a/clutter/clutter/clutter-stage.c b/clutter/clutter/clutter-stage.c
index 828071a48..8fa92dd7f 100644
--- a/clutter/clutter/clutter-stage.c
+++ b/clutter/clutter/clutter-stage.c
@@ -3627,6 +3627,10 @@ _clutter_stage_maybe_setup_viewport (ClutterStage     *stage,
       float fb_scale;
       float viewport_offset_x;
       float viewport_offset_y;
+      float viewport_x;
+      float viewport_y;
+      float viewport_width;
+      float viewport_height;
       float z_2d;
 
       CLUTTER_NOTE (PAINT,
@@ -3639,11 +3643,13 @@ _clutter_stage_maybe_setup_viewport (ClutterStage     *stage,
 
       viewport_offset_x = view_layout.x * fb_scale;
       viewport_offset_y = view_layout.y * fb_scale;
+      viewport_x = roundf (priv->viewport[0] * fb_scale - viewport_offset_x);
+      viewport_y = roundf (priv->viewport[1] * fb_scale - viewport_offset_y);
+      viewport_width = roundf (priv->viewport[2] * fb_scale);
+      viewport_height = roundf (priv->viewport[3] * fb_scale);
       cogl_framebuffer_set_viewport (fb,
-                                     priv->viewport[0] * fb_scale - viewport_offset_x,
-                                     priv->viewport[1] * fb_scale - viewport_offset_y,
-                                     priv->viewport[2] * fb_scale,
-                                     priv->viewport[3] * fb_scale);
+                                     viewport_x, viewport_y,
+                                     viewport_width, viewport_height);
 
       perspective = priv->perspective;