worker-hermite.js

onmessage = function (event){
	var img = event.data[0];
	var data = img.data;
	var W = event.data[1];
	var H = event.data[2];
	var W2 = event.data[3];
	var H2 = event.data[4];
	var core = event.data[5];
	var max_cores = event.data[6];
	var data2 = [];
	var ratio_w = W / W2;
	var ratio_h = H / H2;
	var ratio_w_half = Math.ceil(ratio_w/2);
	var ratio_h_half = Math.ceil(ratio_h/2);
	var start_row = Math.ceil(H2*core/max_cores)-1; if(start_row < 0) start_row = 0;
	var offset = Math.floor(H2*core/max_cores) * W2 * 4;
	
	for(var j = start_row; j < start_row + Math.ceil(H2/max_cores); j++){
		for(var i = 0; i < W2; i++){
			var x2 = (i + j*W2) * 4;
			var weight = 0;
			var weights = 0;
			var gx_r = gx_g = gx_b = gx_a = 0;
			var center_y = (j + 0.5) * ratio_h;
			for(var yy = Math.floor(j * ratio_h); yy < (j + 1) * ratio_h; yy++){
				var dy = Math.abs(center_y - (yy + 0.5)) / ratio_h_half;
				var center_x = (i + 0.5) * ratio_w;
				var w0 = dy*dy //pre-calc part of w
				for(var xx = Math.floor(i * ratio_w); xx < (i + 1) * ratio_w; xx++){
					var dx = Math.abs(center_x - (xx + 0.5)) / ratio_w_half;
					var w = Math.sqrt(w0 + dx*dx);
					if(w >= -1 && w <= 1){
						//hermite filter
						weight = 2 * w*w*w - 3*w*w + 1;
						if(weight > 0){
							dx = 4*(xx + yy*W);
							gx_r += weight * data[dx];
							gx_g += weight * data[dx + 1];
							gx_b += weight * data[dx + 2];
							gx_a += weight * data[dx + 3];
							weights += weight;
							}
						}
					}
				}
			var x2 = (i + j*W2) * 4 - offset;
			data2[x2]     = gx_r / weights;
			data2[x2 + 1] = gx_g / weights;
			data2[x2 + 2] = gx_b / weights;
			data2[x2 + 3] = gx_a / weights;
			}
		}
	postMessage({offset: offset, data: data2});
	};