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// Jump flooding algorithm for EDT according
// to Danielsson (1980) and Guodong Rong (2007).
// Implementation by Stefan Gustavson 2010.
// This code is in the public domain.
// This code represents one iteration of the flood filling.
// You need to run it multiple times with different step
// lengths to perform a full distance transformation.
uniform sampler2D texture;
varying float stepu;
varying float stepv;
varying vec2 uv;
// Helper functions to remap unsigned normalized floats [0.0,1.0]
// coming from an integer texture to the range we need [-1, 1].
// The transformations are very specifically designed to map
// integer texel values exactly to pixel centers, and vice versa.
// (See fragment_seed.glsl for details.)
vec2 remap(vec4 floatdata) {
vec2 scaleddata = vec2(floatdata.x * 65280. + floatdata.z * 255.,
floatdata.y * 65280. + floatdata.w * 255.);
return scaleddata / 32768. - 1.0;
}
vec4 remap_inv(vec2 floatvec) {
vec2 data = (floatvec + 1.0) * 32768.;
float x = floor(data.x / 256.);
float y = floor(data.y / 256.);
return vec4(x, y, data.x - x * 256., data.y - y * 256.) / 255.;
}
void main( void )
{
// Search for better distance vectors among 8 candidates
vec2 stepvec; // Relative offset to candidate being tested
vec2 newvec; // Absolute position of that candidate
vec3 newseed; // Closest point from that candidate (.xy) and its distance (.z)
vec3 bestseed; // Closest seed so far
bestseed.xy = remap(texture2D(texture, uv).rgba);
bestseed.z = length(bestseed.xy);
// This code depends on the texture having a CLAMP_TO_BORDER
// attribute and a border color with R = 0.
// The commented-out lines handle clamping to the edge explicitly
// to avoid propagating incorrect vectors when looking outside
// of [0,1] in u and/or v.
// These explicit conditionals cause a slowdown of about 25%.
// Sometimes a periodic transform with edge repeats might be
// what you want. In that case, the texture wrap mode can be
// set to GL_REPEAT, and the shader code can be left unchanged.
stepvec = vec2(-stepu, -stepv);
newvec = uv + stepvec;
if ( all( bvec4( lessThan(newvec, vec2(1.0)), greaterThan(newvec, vec2(0.0)) ) ) ) {
newseed.xy = remap(texture2D(texture, newvec).rgba);
if(newseed.x > -0.99999) { // if the new seed is not "indeterminate distance"
newseed.xy = newseed.xy + stepvec;
newseed.z = length(newseed.xy);
if(newseed.z < bestseed.z) {
bestseed = newseed;
}
}
}
stepvec = vec2(-stepu, 0.0);
newvec = uv + stepvec;
if ( all( bvec4( lessThan(newvec, vec2(1.0)), greaterThan(newvec, vec2(0.0)) ) ) ) {
newseed.xy = remap(texture2D(texture, newvec).rgba);
if(newseed.x > -0.99999) { // if the new seed is not "indeterminate distance"
newseed.xy = newseed.xy + stepvec;
newseed.z = length(newseed.xy);
if(newseed.z < bestseed.z) {
bestseed = newseed;
}
}
}
stepvec = vec2(-stepu, stepv);
newvec = uv + stepvec;
if ( all( bvec4( lessThan(newvec, vec2(1.0)), greaterThan(newvec, vec2(0.0)) ) ) ) {
newseed.xy = remap(texture2D(texture, newvec).rgba);
if(newseed.x > -0.99999) { // if the new seed is not "indeterminate distance"
newseed.xy = newseed.xy + stepvec;
newseed.z = length(newseed.xy);
if(newseed.z < bestseed.z) {
bestseed = newseed;
}
}
}
stepvec = vec2(0.0, -stepv);
newvec = uv + stepvec;
if ( all( bvec4( lessThan(newvec, vec2(1.0)), greaterThan(newvec, vec2(0.0)) ) ) ) {
newseed.xy = remap(texture2D(texture, newvec).rgba);
if(newseed.x > -0.99999) { // if the new seed is not "indeterminate distance"
newseed.xy = newseed.xy + stepvec;
newseed.z = length(newseed.xy);
if(newseed.z < bestseed.z) {
bestseed = newseed;
}
}
}
stepvec = vec2(0.0, stepv);
newvec = uv + stepvec;
if ( all( bvec4( lessThan(newvec, vec2(1.0)), greaterThan(newvec, vec2(0.0)) ) ) ) {
newseed.xy = remap(texture2D(texture, newvec).rgba);
if(newseed.x > -0.99999) { // if the new seed is not "indeterminate distance"
newseed.xy = newseed.xy + stepvec;
newseed.z = length(newseed.xy);
if(newseed.z < bestseed.z) {
bestseed = newseed;
}
}
}
stepvec = vec2(stepu, -stepv);
newvec = uv + stepvec;
if ( all( bvec4( lessThan(newvec, vec2(1.0)), greaterThan(newvec, vec2(0.0)) ) ) ) {
newseed.xy = remap(texture2D(texture, newvec).rgba);
if(newseed.x > -0.99999) { // if the new seed is not "indeterminate distance"
newseed.xy = newseed.xy + stepvec;
newseed.z = length(newseed.xy);
if(newseed.z < bestseed.z) {
bestseed = newseed;
}
}
}
stepvec = vec2(stepu, 0.0);
newvec = uv + stepvec;
if ( all( bvec4( lessThan(newvec, vec2(1.0)), greaterThan(newvec, vec2(0.0)) ) ) ) {
newseed.xy = remap(texture2D(texture, newvec).rgba);
if(newseed.x > -0.99999) { // if the new seed is not "indeterminate distance"
newseed.xy = newseed.xy + stepvec;
newseed.z = length(newseed.xy);
if(newseed.z < bestseed.z) {
bestseed = newseed;
}
}
}
stepvec = vec2(stepu, stepv);
newvec = uv + stepvec;
if ( all( bvec4( lessThan(newvec, vec2(1.0)), greaterThan(newvec, vec2(0.0)) ) ) ) {
newseed.xy = remap(texture2D(texture, newvec).rgba);
if(newseed.x > -0.99999) { // if the new seed is not "indeterminate distance"
newseed.xy = newseed.xy + stepvec;
newseed.z = length(newseed.xy);
if(newseed.z < bestseed.z) {
bestseed = newseed;
}
}
}
gl_FragColor = remap_inv(bestseed.xy);
}
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