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Removes scolling jank after bw image optimization

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This commit is contained in:
Yury Delendik 2014-01-29 13:10:34 -06:00
parent c5a804c43a
commit 99bbad3219
1 changed files with 30 additions and 14 deletions
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44
src/display/canvas.js
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@ -442,13 +442,14 @@ var CanvasGraphics = (function CanvasGraphicsClosure() {
// will (conceptually) put pixels past the bounds of the canvas. But
// that's ok; any such pixels are ignored.
var height = imgData.height, width = imgData.width;
var fullChunkHeight = 16;
var fracChunks = imgData.height / fullChunkHeight;
var fracChunks = height / fullChunkHeight;
var fullChunks = Math.floor(fracChunks);
var totalChunks = Math.ceil(fracChunks);
var partialChunkHeight = imgData.height - fullChunks * fullChunkHeight;
var partialChunkHeight = height - fullChunks * fullChunkHeight;
var chunkImgData = ctx.createImageData(imgData.width, fullChunkHeight);
var chunkImgData = ctx.createImageData(width, fullChunkHeight);
var srcPos = 0;
var src = imgData.data;
var dst = chunkImgData.data;
@ -460,8 +461,11 @@ var CanvasGraphics = (function CanvasGraphicsClosure() {
// Grayscale, 1 bit per pixel (i.e. black-and-white).
var srcData = imgData.data;
var destData = chunkImgData.data;
var alpha = 255;
var destDataLength = destData.length;
var origLength = imgData.origLength;
for (var i = 3; i < destDataLength; i += 4) {
destData[i] = 255;
}
for (var i = 0; i < totalChunks; i++) {
var thisChunkHeight =
(i < fullChunks) ? fullChunkHeight : partialChunkHeight;
@ -469,25 +473,37 @@ var CanvasGraphics = (function CanvasGraphicsClosure() {
for (var j = 0; j < thisChunkHeight; j++) {
var mask = 0;
var srcByte = 0;
for (var k = 0; k < imgData.width; k++) {
if (srcPos >= origLength) {
// We ran out of input. Make all remaining pixels transparent.
alpha = 0;
}
for (var k = 0; k < width; k++, destPos += 4) {
if (mask === 0) {
if (srcPos >= origLength) {
break;
}
srcByte = srcData[srcPos++];
mask = 128;
}
var c = (+!!(srcByte & mask)) * 255;
destData[destPos++] = c;
destData[destPos++] = c;
destData[destPos++] = c;
destData[destPos++] = alpha;
if ((srcByte & mask)) {
destData[destPos] = 255;
destData[destPos + 1] = 255;
destData[destPos + 2] = 255;
} else {
destData[destPos] = 0;
destData[destPos + 1] = 0;
destData[destPos + 2] = 0;
}
mask >>= 1;
}
}
if (destPos < destDataLength) {
// We ran out of input. Make all remaining pixels transparent.
destPos += 3;
do {
destData[destPos] = 0;
destPos += 4;
} while (destPos < destDataLength);
}
ctx.putImageData(chunkImgData, 0, i * fullChunkHeight);
}