Pixel-Composer/shaders/sh_image_trace/sh_image_trace.fsh

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varying vec2 v_vTexcoord;
varying vec4 v_vColour;
uniform vec2 dimension;
vec2 tx;
bool sample(float x, float y) {
vec2 pos = v_vTexcoord + vec2(tx.x * x, tx.y * y);
if(pos.x < 0. || pos.y < 0. || pos.x > 1. || pos.y > 1.) return false;
vec4 c = texture2D( gm_BaseTexture, pos );
return (c.r + c.g + c.b) * c.a > 0.;
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}
void main() {
tx = 1. / dimension;
vec4 cc = texture2D( gm_BaseTexture, v_vTexcoord );
gl_FragColor = vec4(0.);
if(cc.r == 0.) return;
if(!sample(-1., 0.)) { gl_FragColor = vec4(1.); return; }
if(!sample( 1., 0.)) { gl_FragColor = vec4(1.); return; }
if(!sample(0., -1.)) { gl_FragColor = vec4(1.); return; }
if(!sample(0., 1.)) { gl_FragColor = vec4(1.); return; }
}