(function(){ "use strict"; var canvas = document.createElement("canvas"); canvas.width = 11; canvas.height = 13; var gl = canvas.getContext("webgl"); // paint it completely black gl.clearColor(0, 0, 0, 1); gl.clear(gl.COLOR_BUFFER_BIT); var pixels = new Uint8Array(gl.drawingBufferWidth * gl.drawingBufferHeight * 4); gl.readPixels(0, 0, gl.drawingBufferWidth, gl.drawingBufferHeight, gl.RGBA, gl.UNSIGNED_BYTE, pixels); var values = {}; for (var i = 0; i < pixels.length; i += 1){ values[pixels[i]] = (values[pixels[i]] || 0) + 1; } document.getElementById("output").textContent = JSON.stringify(values); }());