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Merge pull request #8620 from Rob--W/issue-8560-improve-png-compression

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Improve compression of PNG images embedded in generated SVG files
This commit is contained in:
Yury Delendik 2017-07-14 07:23:38 -05:00 • committed by GitHub
commit ca3c08f12b
9 changed files with 329 additions and 71 deletions
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124
src/display/svg.js
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@ -12,10 +12,11 @@
* See the License for the specific language governing permissions and
* limitations under the License.
*/
/* globals __non_webpack_require__ */
import {
createObjectURL, FONT_IDENTITY_MATRIX, IDENTITY_MATRIX, ImageKind, isArray,
isNum, OPS, Util, warn
isNodeJS, isNum, OPS, Util, warn
} from '../shared/util';
var SVGGraphics = function() {
@ -97,6 +98,89 @@ var convertImgDataToPng = (function convertImgDataToPngClosure() {
return (b << 16) | a;
}
/**
* @param {Uint8Array} literals The input data.
* @returns {Uint8Array} The DEFLATE-compressed data stream in zlib format.
* This is the required format for compressed streams in the PNG format:
* http://www.libpng.org/pub/png/spec/1.2/PNG-Compression.html
*/
function deflateSync(literals) {
if (!isNodeJS()) {
// zlib is certainly not available outside of Node.js. We can either use
// the pako library for client-side DEFLATE compression, or use the canvas
// API of the browser to obtain a more optimal PNG file.
return deflateSyncUncompressed(literals);
}
try {
// NOTE: This implementation is far from perfect, but already way better
// than not applying any compression.
//
// A better algorithm will try to choose a good predictor/filter and
// then choose a suitable zlib compression strategy (e.g. 3,Z_RLE).
//
// Node v0.11.12 zlib.deflateSync is introduced (and returns a Buffer).
// Node v3.0.0 Buffer inherits from Uint8Array.
// Node v8.0.0 zlib.deflateSync accepts Uint8Array as input.
var input;
// eslint-disable-next-line no-undef
if (parseInt(process.versions.node) >= 8) {
input = literals;
} else {
// eslint-disable-next-line no-undef
input = new Buffer(literals);
}
var output = __non_webpack_require__('zlib')
.deflateSync(input, { level: 9, });
return output instanceof Uint8Array ? output : new Uint8Array(output);
} catch (e) {
warn('Not compressing PNG because zlib.deflateSync is unavailable: ' + e);
}
return deflateSyncUncompressed(literals);
}
// An implementation of DEFLATE with compression level 0 (Z_NO_COMPRESSION).
function deflateSyncUncompressed(literals) {
var len = literals.length;
var maxBlockLength = 0xFFFF;
var deflateBlocks = Math.ceil(len / maxBlockLength);
var idat = new Uint8Array(2 + len + deflateBlocks * 5 + 4);
var pi = 0;
idat[pi++] = 0x78; // compression method and flags
idat[pi++] = 0x9c; // flags
var pos = 0;
while (len > maxBlockLength) {
// writing non-final DEFLATE blocks type 0 and length of 65535
idat[pi++] = 0x00;
idat[pi++] = 0xff;
idat[pi++] = 0xff;
idat[pi++] = 0x00;
idat[pi++] = 0x00;
idat.set(literals.subarray(pos, pos + maxBlockLength), pi);
pi += maxBlockLength;
pos += maxBlockLength;
len -= maxBlockLength;
}
// writing non-final DEFLATE blocks type 0
idat[pi++] = 0x01;
idat[pi++] = len & 0xff;
idat[pi++] = len >> 8 & 0xff;
idat[pi++] = (~len & 0xffff) & 0xff;
idat[pi++] = (~len & 0xffff) >> 8 & 0xff;
idat.set(literals.subarray(pos), pi);
pi += literals.length - pos;
var adler = adler32(literals, 0, literals.length); // checksum
idat[pi++] = adler >> 24 & 0xff;
idat[pi++] = adler >> 16 & 0xff;
idat[pi++] = adler >> 8 & 0xff;
idat[pi++] = adler & 0xff;
return idat;
}
function encode(imgData, kind, forceDataSchema) {
var width = imgData.width;
var height = imgData.height;
@ -162,43 +246,7 @@ var convertImgDataToPng = (function convertImgDataToPngClosure() {
0x00 // interlace method
]);
var len = literals.length;
var maxBlockLength = 0xFFFF;
var deflateBlocks = Math.ceil(len / maxBlockLength);
var idat = new Uint8Array(2 + len + deflateBlocks * 5 + 4);
var pi = 0;
idat[pi++] = 0x78; // compression method and flags
idat[pi++] = 0x9c; // flags
var pos = 0;
while (len > maxBlockLength) {
// writing non-final DEFLATE blocks type 0 and length of 65535
idat[pi++] = 0x00;
idat[pi++] = 0xff;
idat[pi++] = 0xff;
idat[pi++] = 0x00;
idat[pi++] = 0x00;
idat.set(literals.subarray(pos, pos + maxBlockLength), pi);
pi += maxBlockLength;
pos += maxBlockLength;
len -= maxBlockLength;
}
// writing non-final DEFLATE blocks type 0
idat[pi++] = 0x01;
idat[pi++] = len & 0xff;
idat[pi++] = len >> 8 & 0xff;
idat[pi++] = (~len & 0xffff) & 0xff;
idat[pi++] = (~len & 0xffff) >> 8 & 0xff;
idat.set(literals.subarray(pos), pi);
pi += literals.length - pos;
var adler = adler32(literals, 0, literals.length); // checksum
idat[pi++] = adler >> 24 & 0xff;
idat[pi++] = adler >> 16 & 0xff;
idat[pi++] = adler >> 8 & 0xff;
idat[pi++] = adler & 0xff;
var idat = deflateSync(literals);
// PNG will consists: header, IHDR+data, IDAT+data, and IEND.
var pngLength = PNG_HEADER.length + (CHUNK_WRAPPER_SIZE * 3) +