[mutter] MetaBackgroundActor: glsl: do not mix int and float.

[Adel Gadllah <agadllah src gnome org>]

commit f858f66fe050459beeb349a4448c165d95de0450
Author: Alban Browaeys <prahal yahoo com>
Date:   Mon Mar 2 11:34:40 2015 +0100

    MetaBackgroundActor: glsl: do not mix int and float.
    
    Implicit conversion from int to float is not supported by
    GLSL ES.
    
    Fixes:
    (gnome-shell:8954): Cogl-WARNING **: Shader compilation failed:
    1:2: P0004: High precision not supported, instead compiling high precision as medium precision
    4:17: S0001: Type mismatch in arithmetic operation between 'int' and 'float'
    when one trigger the overview mode on Mali 400 r1p1 GPU.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=745442

 src/compositor/meta-background-actor.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/src/compositor/meta-background-actor.c b/src/compositor/meta-background-actor.c
index abc6fda..132494d 100644
--- a/src/compositor/meta-background-actor.c
+++ b/src/compositor/meta-background-actor.c
@@ -115,7 +115,7 @@ typedef enum {
 #define FRAGMENT_SHADER_CODE                                                   \
 "float t = 2.0 * length(position);\n"                                          \
 "t = min(t, 1.0);\n"                                                           \
-"float pixel_brightness = 1 - t * vignette_sharpness;\n"                       \
+"float pixel_brightness = 1.0 - t * vignette_sharpness;\n"                       \
 "cogl_color_out.rgb = cogl_color_out.rgb * pixel_brightness;\n"                \
 
 typedef struct _MetaBackgroundLayer MetaBackgroundLayer;