#version 150

uniform sampler2D t0, ts;
uniform vec2 dt;
uniform float factor = 1.;
uniform int steps = 8;

void main(void) {
	vec2 cdt = dt / steps;
	vec2 ct = qgl_FragTexture.xy;
	vec3 speed = texelFetch(ts, ivec2(gl_FragCoord.xy), 0).rgb * 256 * factor;
	int hsteps = steps / 2;
	ct -= speed.xy * cdt * hsteps;
	vec3 scol = vec3(0);//texture(t0, ct).rgb;
	float sum = 0.;
	for (int i = 0; i < steps; ++i) {
		ct += speed.xy * cdt;
		float mul = 1. - abs(i - hsteps) * 2. / steps;
		scol += texture(t0, ct).rgb * mul;
		sum += mul;
	}
	scol /= sum;
	qgl_FragData[0].rgb = scol;
}