// circular blur, alpha-controlled

#vertex

void main() {
    gl_TexCoord[0] = gl_MultiTexCoord0;
    gl_Position = ftransform();
}

#fragment

uniform sampler2D tex;
uniform vec2 rmax;

const vec2 v1 = vec2( 0.988, 0.156);
const vec2 v2 = vec2( 0.588, 0.809);
const vec2 v3 = vec2(-0.156, 0.988);
const vec2 v4 = vec2(-0.809, 0.588);

void main() {
    vec2 t = gl_TexCoord[0].xy;
    vec2 r = rmax * texture2D(tex, t).a;
    gl_FragColor = 0.125 * (
        texture2D(tex, t + r * v1) + texture2D(tex, t - r * v1) +
        texture2D(tex, t + r * v2) + texture2D(tex, t - r * v2) +
        texture2D(tex, t + r * v3) + texture2D(tex, t - r * v3) +
        texture2D(tex, t + r * v4) + texture2D(tex, t - r * v4));
}