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Move DEFLATE logic in convertImgDataToPng

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Move the DEFLATE logic in convertImgDataToPng to a separate function.
A later commit will introduce a more efficient deflate algorithm,
and fall back to the existing, naive algorithm if needed.
This commit is contained in:
Rob Wu 2017-07-04 19:13:34 +02:00
parent 2cef24a2ad
commit 94f1dde07d
1 changed files with 53 additions and 37 deletions
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90
src/display/svg.js
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@ -97,6 +97,58 @@ 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) {
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 +214,7 @@ 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) +