WIP - add extractor, generate snippet_data

node_modules/pixelmatch/index.js

@@ -0,0 +1,158 @@
+'use strict';
+
+module.exports = pixelmatch;
+
+function pixelmatch(img1, img2, output, width, height, options) {
+
+    if (!options) options = {};
+
+    var threshold = options.threshold === undefined ? 0.1 : options.threshold;
+
+    // maximum acceptable square distance between two colors;
+    // 35215 is the maximum possible value for the YIQ difference metric
+    var maxDelta = 35215 * threshold * threshold,
+        diff = 0;
+
+    // compare each pixel of one image against the other one
+    for (var y = 0; y < height; y++) {
+        for (var x = 0; x < width; x++) {
+
+            var pos = (y * width + x) * 4;
+
+            // squared YUV distance between colors at this pixel position
+            var delta = colorDelta(img1, img2, pos, pos);
+
+            // the color difference is above the threshold
+            if (delta > maxDelta) {
+                // check it's a real rendering difference or just anti-aliasing
+                if (!options.includeAA && (antialiased(img1, x, y, width, height, img2) ||
+                                   antialiased(img2, x, y, width, height, img1))) {
+                    // one of the pixels is anti-aliasing; draw as yellow and do not count as difference
+                    if (output) drawPixel(output, pos, 255, 255, 0);
+
+                } else {
+                    // found substantial difference not caused by anti-aliasing; draw it as red
+                    if (output) drawPixel(output, pos, 255, 0, 0);
+                    diff++;
+                }
+
+            } else if (output) {
+                // pixels are similar; draw background as grayscale image blended with white
+                var val = blend(grayPixel(img1, pos), 0.1);
+                drawPixel(output, pos, val, val, val);
+            }
+        }
+    }
+
+    // return the number of different pixels
+    return diff;
+}
+
+// check if a pixel is likely a part of anti-aliasing;
+// based on "Anti-aliased Pixel and Intensity Slope Detector" paper by V. Vysniauskas, 2009
+
+function antialiased(img, x1, y1, width, height, img2) {
+    var x0 = Math.max(x1 - 1, 0),
+        y0 = Math.max(y1 - 1, 0),
+        x2 = Math.min(x1 + 1, width - 1),
+        y2 = Math.min(y1 + 1, height - 1),
+        pos = (y1 * width + x1) * 4,
+        zeroes = 0,
+        positives = 0,
+        negatives = 0,
+        min = 0,
+        max = 0,
+        minX, minY, maxX, maxY;
+
+    // go through 8 adjacent pixels
+    for (var x = x0; x <= x2; x++) {
+        for (var y = y0; y <= y2; y++) {
+            if (x === x1 && y === y1) continue;
+
+            // brightness delta between the center pixel and adjacent one
+            var delta = colorDelta(img, img, pos, (y * width + x) * 4, true);
+
+            // count the number of equal, darker and brighter adjacent pixels
+            if (delta === 0) zeroes++;
+            else if (delta < 0) negatives++;
+            else if (delta > 0) positives++;
+
+            // if found more than 2 equal siblings, it's definitely not anti-aliasing
+            if (zeroes > 2) return false;
+
+            if (!img2) continue;
+
+            // remember the darkest pixel
+            if (delta < min) {
+                min = delta;
+                minX = x;
+                minY = y;
+            }
+            // remember the brightest pixel
+            if (delta > max) {
+                max = delta;
+                maxX = x;
+                maxY = y;
+            }
+        }
+    }
+
+    if (!img2) return true;
+
+    // if there are no both darker and brighter pixels among siblings, it's not anti-aliasing
+    if (negatives === 0 || positives === 0) return false;
+
+    // if either the darkest or the brightest pixel has more than 2 equal siblings in both images
+    // (definitely not anti-aliased), this pixel is anti-aliased
+    return (!antialiased(img, minX, minY, width, height) && !antialiased(img2, minX, minY, width, height)) ||
+           (!antialiased(img, maxX, maxY, width, height) && !antialiased(img2, maxX, maxY, width, height));
+}
+
+// calculate color difference according to the paper "Measuring perceived color difference
+// using YIQ NTSC transmission color space in mobile applications" by Y. Kotsarenko and F. Ramos
+
+function colorDelta(img1, img2, k, m, yOnly) {
+    var a1 = img1[k + 3] / 255,
+        a2 = img2[m + 3] / 255,
+
+        r1 = blend(img1[k + 0], a1),
+        g1 = blend(img1[k + 1], a1),
+        b1 = blend(img1[k + 2], a1),
+
+        r2 = blend(img2[m + 0], a2),
+        g2 = blend(img2[m + 1], a2),
+        b2 = blend(img2[m + 2], a2),
+
+        y = rgb2y(r1, g1, b1) - rgb2y(r2, g2, b2);
+
+    if (yOnly) return y; // brightness difference only
+
+    var i = rgb2i(r1, g1, b1) - rgb2i(r2, g2, b2),
+        q = rgb2q(r1, g1, b1) - rgb2q(r2, g2, b2);
+
+    return 0.5053 * y * y + 0.299 * i * i + 0.1957 * q * q;
+}
+
+function rgb2y(r, g, b) { return r * 0.29889531 + g * 0.58662247 + b * 0.11448223; }
+function rgb2i(r, g, b) { return r * 0.59597799 - g * 0.27417610 - b * 0.32180189; }
+function rgb2q(r, g, b) { return r * 0.21147017 - g * 0.52261711 + b * 0.31114694; }
+
+// blend semi-transparent color with white
+function blend(c, a) {
+    return 255 + (c - 255) * a;
+}
+
+function drawPixel(output, pos, r, g, b) {
+    output[pos + 0] = r;
+    output[pos + 1] = g;
+    output[pos + 2] = b;
+    output[pos + 3] = 255;
+}
+
+function grayPixel(img, i) {
+    var a = img[i + 3] / 255,
+        r = blend(img[i + 0], a),
+        g = blend(img[i + 1], a),
+        b = blend(img[i + 2], a);
+    return rgb2y(r, g, b);
+}