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compositor: improve vignette on background actor

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The shader used for computing a vignette currently has two
problems:

 * The math is wrong such that the vignette isn't stretched
   across the whole actor and so ends abruptly
 * There is noticeable banding in its gradient

This commit corrects both problems by fixing the computing
and introducing noise dithering.
This commit is contained in:
Nikita Churaev 2018-03-07 00:14:44 +03:00 committed by Georges Basile Stavracas Neto
parent 8e9184b62e
commit bdf8d0f1c3
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GPG Key ID: 886C17EE170D1385
1 changed files with 8 additions and 4 deletions
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6
src/compositor/meta-background-actor.c
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@ -131,15 +131,19 @@ typedef enum {
#define VIGNETTE_VERTEX_SHADER_CODE \
"position = cogl_tex_coord0_in.xy * scale + offset;\n" \
#define VIGNETTE_SQRT_2 "1.4142"
#define VIGNETTE_FRAGMENT_SHADER_DECLARATIONS \
"uniform float vignette_sharpness;\n" \
"varying vec2 position;\n" \
"float rand(vec2 p) { return fract(sin(dot(p, vec2(12.9898, 78.233))) * 43758.5453123); }\n" \
#define VIGNETTE_FRAGMENT_SHADER_CODE \
"float t = 2.0 * length(position);\n" \
"float t = " VIGNETTE_SQRT_2 " * length(position);\n" \
"t = min(t, 1.0);\n" \
"float pixel_brightness = 1.0 - t * vignette_sharpness;\n" \
"cogl_color_out.rgb = cogl_color_out.rgb * pixel_brightness;\n" \
"cogl_color_out.rgb += (rand(position) - 0.5) / 255.0;\n" \
typedef struct _MetaBackgroundLayer MetaBackgroundLayer;