gtk2/demos/gtk-demo/ripple.glsl

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uniform float u_time;
uniform vec2 u_mouse;
uniform sampler2D u_texture1;
#define PI 3.141592654
float decay(float v, float t)
{
return v * (1.0 / (1.0 + t*t));
}
void mainImage(out vec4 fragColor, in vec2 fragCoord, in vec2 resolution, in vec2 uv)
{
// Temporary to loop time every 1 sec
float time = u_time;
// we normalize all the effects according to the min height/width
float size = min(resolution.x, resolution.y);
// Animate one wave over size in 0.3 sec
float wave_speed = size / 0.3;
float wave_length = size / 1.0;
float wave_height = size * 0.1;
vec2 center = u_mouse;
vec2 direction_from_center = fragCoord - center;
float distance_from_center = length(direction_from_center);
/* Normalize direction */
direction_from_center = direction_from_center / distance_from_center;
float propagation_length = time * wave_speed;
float t = (propagation_length - distance_from_center) / wave_length;
float offset_magnitude = 0;
if (t > 0.0)
offset_magnitude = decay(wave_height * sin(t * 2.0 * PI), t);
vec2 offset = direction_from_center * min(offset_magnitude, distance_from_center);
vec2 source = fragCoord - offset;
vec2 uv2 = source / resolution;
fragColor = GskTexture(u_texture1, vec2(uv2.x, 1.0-uv2.y));
}