1 #include "shaders_common.h"
2 
3 static const char *stock_fragment_xmb_simple_snow = GLSL(
4    uniform float time;
5    uniform vec2 OutputSize;
6 
7    float baseScale = 1.25; /* [1.0  .. 10.0] */
8    float density   = 0.5;  /* [0.01 ..  1.0] */
9    float speed     = 0.15; /* [0.1  ..  1.0] */
10 
11    float rand(vec2 co)
12    {
13       return fract(sin(dot(co.xy, vec2(12.9898, 78.233))) * 43758.5453);
14    }
15 
16    float dist_func(vec2 distv)
17    {
18       float dist = sqrt((distv.x * distv.x) + (distv.y * distv.y)) * (40.0 / baseScale);
19       dist = clamp(dist, 0.0, 1.0);
20       return cos(dist * (3.14159265358 * 0.5)) * 0.5;
21    }
22 
23    float random_dots(vec2 co)
24    {
25       float part = 1.0 / 20.0;
26       vec2 cd = floor(co / part);
27       float p = rand(cd);
28 
29       if (p > 0.005 * (density * 40.0))
30          return 0.0;
31 
32       vec2 dpos = (vec2(fract(p * 2.0) , p) + vec2(2.0, 2.0)) * 0.25;
33 
34       vec2 cellpos = fract(co / part);
35       vec2 distv = (cellpos - dpos);
36 
37       return dist_func(distv);
38    }
39 
40    float snow(vec2 pos, float time, float scale)
41    {
42       /* add wobble */
43       pos.x += cos(pos.y * 1.2 + time * 3.14159 * 2.0 + 1.0 / scale) / (8.0 / scale) * 4.0;
44       /* add gravity */
45       pos += time * scale * vec2(-0.5, 1.0) * 4.0;
46       return random_dots(pos / scale) * (scale * 0.5 + 0.5);
47    }
48 
49    void main(void)
50    {
51       float tim = time * 0.4 * speed;
52       vec2 pos = gl_FragCoord.xy / OutputSize.xx;
53       float a = 0.0;
54       /**
55        * Each of these is a layer of snow
56        * Remove some for better performance
57        * Changing the scale (3rd value) will mess with the looping
58        **/
59       a += snow(pos, tim, 1.0);
60       a += snow(pos, tim, 0.7);
61       a += snow(pos, tim, 0.6);
62       a += snow(pos, tim, 0.5);
63       a += snow(pos, tim, 0.4);
64       a += snow(pos, tim, 0.3);
65       a += snow(pos, tim, 0.25);
66       a += snow(pos, tim, 0.125);
67       a = a * min(pos.y * 4.0, 1.0);
68       gl_FragColor = vec4(1.0, 1.0, 1.0, a);
69    }
70 
71 );
72