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build/node_modules/pngjs/lib/interlace.js

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+'use strict';
+
+// Adam 7
+//   0 1 2 3 4 5 6 7
+// 0 x 6 4 6 x 6 4 6
+// 1 7 7 7 7 7 7 7 7
+// 2 5 6 5 6 5 6 5 6
+// 3 7 7 7 7 7 7 7 7
+// 4 3 6 4 6 3 6 4 6
+// 5 7 7 7 7 7 7 7 7
+// 6 5 6 5 6 5 6 5 6
+// 7 7 7 7 7 7 7 7 7
+
+
+var imagePasses = [
+  { // pass 1 - 1px
+    x: [0],
+    y: [0]
+  },
+  { // pass 2 - 1px
+    x: [4],
+    y: [0]
+  },
+  { // pass 3 - 2px
+    x: [0, 4],
+    y: [4]
+  },
+  { // pass 4 - 4px
+    x: [2, 6],
+    y: [0, 4]
+  },
+  { // pass 5 - 8px
+    x: [0, 2, 4, 6],
+    y: [2, 6]
+  },
+  { // pass 6 - 16px
+    x: [1, 3, 5, 7],
+    y: [0, 2, 4, 6]
+  },
+  { // pass 7 - 32px
+    x: [0, 1, 2, 3, 4, 5, 6, 7],
+    y: [1, 3, 5, 7]
+  }
+];
+
+exports.getImagePasses = function(width, height) {
+  var images = [];
+  var xLeftOver = width % 8;
+  var yLeftOver = height % 8;
+  var xRepeats = (width - xLeftOver) / 8;
+  var yRepeats = (height - yLeftOver) / 8;
+  for (var i = 0; i < imagePasses.length; i++) {
+    var pass = imagePasses[i];
+    var passWidth = xRepeats * pass.x.length;
+    var passHeight = yRepeats * pass.y.length;
+    for (var j = 0; j < pass.x.length; j++) {
+      if (pass.x[j] < xLeftOver) {
+        passWidth++;
+      }
+      else {
+        break;
+      }
+    }
+    for (j = 0; j < pass.y.length; j++) {
+      if (pass.y[j] < yLeftOver) {
+        passHeight++;
+      }
+      else {
+        break;
+      }
+    }
+    if (passWidth > 0 && passHeight > 0) {
+      images.push({ width: passWidth, height: passHeight, index: i });
+    }
+  }
+  return images;
+};
+
+exports.getInterlaceIterator = function(width) {
+  return function(x, y, pass) {
+    var outerXLeftOver = x % imagePasses[pass].x.length;
+    var outerX = (((x - outerXLeftOver) / imagePasses[pass].x.length) * 8) + imagePasses[pass].x[outerXLeftOver];
+    var outerYLeftOver = y % imagePasses[pass].y.length;
+    var outerY = (((y - outerYLeftOver) / imagePasses[pass].y.length) * 8) + imagePasses[pass].y[outerYLeftOver];
+    return (outerX * 4) + (outerY * width * 4);
+  };
+};