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April 29, 2012 12:44
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Javascript Signed Distance Fields Generation
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/* | |
* signed distance fields generation in javascript | |
* uses the 8SSEDT algorithm for linear-time processing | |
* | |
* done in conjustion with the signed distance fields text experiment | |
* | |
* references: | |
* http://www.lems.brown.edu/vision/people/leymarie/Refs/CompVision/DT/DTpaper.pdf | |
* http://www.codersnotes.com/notes/signed-distance-fields | |
* http://guides4it.com/Mobile/iphone-3d-programming---crisper-text-with-distance-fields-(part-1)---generating-distance-fields-with-python.aspx | |
* | |
* http://github.com/zz85 | |
* http://twitter.com/blurspline | |
* 29 April 2012 | |
* | |
*/ | |
function signed_distance_fields( grid, width, height ) { | |
"use strict"; | |
var x, y; | |
var grid1 = []; | |
var grid2 = []; | |
var cell, index; | |
var outside = 10000; | |
var outofrange = new THREE.Vector2(outside, outside); | |
var other = new THREE.Vector2(); | |
// some functions | |
function grid_get(grid, x, y) { | |
if (x<0 || y<0 || x> (width-1) || y> (height-1) ) { | |
return outofrange; | |
} | |
return grid[ y * width + x ]; | |
} | |
function grid_put(grid, x, y, p) { | |
grid [ y * width + x ] = p; | |
} | |
function grid_compare(g, cell, x, y, offsetX, offsetY) { | |
other.copy( grid_get(g, x + offsetX, y+offsetY) ); | |
other.x += offsetX; | |
other.y += offsetY; | |
if (other.lengthSq() < cell.lengthSq()) { | |
cell.copy(other); | |
} | |
return cell; | |
} | |
function propagate(grid) { | |
var p; | |
// pass 0 | |
for (y=0; y<height; y++) { | |
for (x=0; x<width; x++) { | |
p = grid_get(grid, x, y); | |
p = grid_compare( grid, p, x, y, -1, 0 ); | |
p = grid_compare( grid, p, x, y, 0, -1 ); | |
p = grid_compare( grid, p, x, y, -1, -1 ); | |
p = grid_compare( grid, p, x, y, 1, -1 ); | |
grid_put( grid, x, y, p ); | |
} | |
for (x=width-1;x>=0;x--) { | |
p = grid_get(grid, x, y); | |
p = grid_compare( grid, p, x, y, 1, 0 ); | |
grid_put( grid, x, y, p); | |
} | |
} | |
// pass 1 | |
for (y=height-1; y>=0; y--) { | |
for (x=width-1;x>=0;x--) { | |
p = grid_get(grid, x, y); | |
p = grid_compare( grid, p, x, y, 1, 0 ); | |
p = grid_compare( grid, p, x, y, 0, 1 ); | |
p = grid_compare( grid, p, x, y, -1, 1 ); | |
p = grid_compare( grid, p, x, y, 1, 1 ); | |
grid_put( grid, x, y, p); | |
} | |
for (x=0; x<width; x++) { | |
p = grid_get(grid, x, y); | |
p = grid_compare( grid, p, x, y, -1, 0 ); | |
grid_put( grid, x, y, p); | |
} | |
} | |
} | |
// Start the work | |
// step 1 generate grids. | |
for (y=0; y<height; y++) { | |
for (x=0; x<width; x++) { | |
index = y * width + x; | |
if ( grid[index] ) { | |
grid_put(grid1, x, y, new THREE.Vector2(0, 0)); | |
grid_put(grid2, x, y, new THREE.Vector2(outside, outside)); | |
} else { | |
grid_put(grid1, x, y, new THREE.Vector2(outside, outside)); | |
grid_put(grid2, x, y, new THREE.Vector2(0, 0)); | |
} | |
} | |
} | |
// step 2 propagate distances | |
propagate(grid1); | |
propagate(grid2); | |
// console.log('grid1', JSON.stringify(grid1), 'grid2', JSON.stringify(grid2)); | |
var distanceFields = []; | |
var dist1, dist2, dist; | |
for (y=0; y<height; y++) { | |
for (x=0; x<width; x++) { | |
dist1 = Math.sqrt( grid_get( grid1, x, y ).lengthSq() ); | |
dist2 = Math.sqrt( grid_get( grid2, x, y ).lengthSq() ); | |
dist = dist1 - dist2; | |
index = y * width + x; | |
distanceFields[index] = dist; | |
} | |
} | |
// console.log('distanceFields', distanceFields); | |
return distanceFields; | |
}; |
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Thanks for the code. Would you update the references websites if known?