JSFiddle - React, Tailwind, and code Playground

by vusan

HTML

<canvas id="cc"></canvas>
<img id="mm"...

CSS

canvas{
    border:1px solid grey;
}

JavaScript

var img = document.getElementById("mm");

var W = 280;
var H = 210;
var canvas = document.getElementById("cc");
var ctx = canvas.getContext("2d");
canvas.width = W;
canvas.height = H;
ctx.drawImage(img, 0, 0);

//resize
resample_hermite(canvas, W, H, W*0.8, H*0.8);




function resample_hermite(canvas, W, H, W2, H2){
	var time1 = Date.now();
	var img = canvas.getContext("2d").getImageData(0, 0, W, H);
	var img2 = canvas.getContext("2d").getImageData(0, 0, W2, H2);
	var data = img.data;
	var data2 = img2.data;
	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);
	for(var j = 0; j < H2; 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;
							}
						}
					}		
				}
			data2[x2]     = gx_r / weights;
			data2[x2 + 1] = gx_g / weights;
			data2[x2 + 2] = gx_b / weights;
			data2[x2 + 3] = gx_a / weights;
			}
		}
	canvas.getContext("2d").clearRect(0, 0, Math.max(W, W2), Math.max(H, H2));
	canvas.getContext("2d").putImageData(img2, 0, 0);
    	console.log("hermite = "+(Math.round(Date.now() - time1)/1000)+" s");
	}