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Merge pull request #4181 from nnethercote/compact-images

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Reduce memory consumption of simple black and white images.
This commit is contained in:
Yury Delendik 2014-01-28 15:53:46 -08:00
commit c5a804c43a
3 changed files with 110 additions and 53 deletions
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96
src/display/canvas.js
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@ -437,45 +437,81 @@ var CanvasGraphics = (function CanvasGraphicsClosure() {
// of putImageData(). (E.g. in Firefox we make two short-lived copies of
// the data passed to putImageData()). |n| shouldn't be too small, however,
// because too many putImageData() calls will slow things down.
//
// Note: as written, if the last chunk is partial, the putImageData() call
// will (conceptually) put pixels past the bounds of the canvas. But
// that's ok; any such pixels are ignored.
var rowsInFullChunks = 16;
var fullChunks = (imgData.height / rowsInFullChunks) | 0;
var rowsInLastChunk = imgData.height - fullChunks * rowsInFullChunks;
var elemsInFullChunks = imgData.width * rowsInFullChunks * 4;
var elemsInLastChunk = imgData.width * rowsInLastChunk * 4;
var fullChunkHeight = 16;
var fracChunks = imgData.height / fullChunkHeight;
var fullChunks = Math.floor(fracChunks);
var totalChunks = Math.ceil(fracChunks);
var partialChunkHeight = imgData.height - fullChunks * fullChunkHeight;
var chunkImgData = ctx.createImageData(imgData.width, rowsInFullChunks);
var chunkImgData = ctx.createImageData(imgData.width, fullChunkHeight);
var srcPos = 0;
var src = imgData.data;
var dst = chunkImgData.data;
var haveSetAndSubarray = 'set' in dst && 'subarray' in src;
// Do all the full-size chunks.
for (var i = 0; i < fullChunks; i++) {
if (haveSetAndSubarray) {
dst.set(src.subarray(srcPos, srcPos + elemsInFullChunks));
srcPos += elemsInFullChunks;
} else {
for (var j = 0; j < elemsInFullChunks; j++) {
chunkImgData.data[j] = imgData.data[srcPos++];
}
}
ctx.putImageData(chunkImgData, 0, i * rowsInFullChunks);
}
// There are multiple forms in which the pixel data can be passed, and
// imgData.kind tells us which one this is.
// Do the final, partial chunk, if required.
if (rowsInLastChunk !== 0) {
if (haveSetAndSubarray) {
dst.set(src.subarray(srcPos, srcPos + elemsInLastChunk));
srcPos += elemsInLastChunk;
} else {
for (var j = 0; j < elemsInLastChunk; j++) {
chunkImgData.data[j] = imgData.data[srcPos++];
if (imgData.kind === 'grayscale_1bpp') {
// Grayscale, 1 bit per pixel (i.e. black-and-white).
var srcData = imgData.data;
var destData = chunkImgData.data;
var alpha = 255;
var origLength = imgData.origLength;
for (var i = 0; i < totalChunks; i++) {
var thisChunkHeight =
(i < fullChunks) ? fullChunkHeight : partialChunkHeight;
var destPos = 0;
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;
}
if (mask === 0) {
srcByte = srcData[srcPos++];
mask = 128;
}
var c = (+!!(srcByte & mask)) * 255;
destData[destPos++] = c;
destData[destPos++] = c;
destData[destPos++] = c;
destData[destPos++] = alpha;
mask >>= 1;
}
}
ctx.putImageData(chunkImgData, 0, i * fullChunkHeight);
}
// This (conceptually) puts pixels past the bounds of the canvas. But
// that's ok; any such pixels are ignored.
ctx.putImageData(chunkImgData, 0, fullChunks * rowsInFullChunks);
} else if (imgData.kind === 'rgba_32bpp') {
// RGBA, 32-bits per pixel.
var haveSetAndSubarray = 'set' in dst && 'subarray' in src;
for (var i = 0; i < totalChunks; i++) {
var thisChunkHeight =
(i < fullChunks) ? fullChunkHeight : partialChunkHeight;
var elemsInThisChunk = imgData.width * thisChunkHeight * 4;
if (haveSetAndSubarray) {
dst.set(src.subarray(srcPos, srcPos + elemsInThisChunk));
srcPos += elemsInThisChunk;
} else {
for (var j = 0; j < elemsInThisChunk; j++) {
chunkImgData.data[j] = imgData.data[srcPos++];
}
}
ctx.putImageData(chunkImgData, 0, i * fullChunkHeight);
}
} else {
error('bad image kind: ' + imgData.kind);
}
}