From 94f1dde07d1a72232b699fcd38ffbf4efb7d2514 Mon Sep 17 00:00:00 2001
From: Rob Wu <rob@robwu.nl>
Date: Tue, 4 Jul 2017 19:13:34 +0200
Subject: [PATCH] Move DEFLATE logic in convertImgDataToPng
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.
---
src/display/svg.js | 90 +++++++++++++++++++++++++++-------------------
1 file changed, 53 insertions(+), 37 deletions(-)
diff --git a/src/display/svg.js b/src/display/svg.js
index bff93abbe..26909fe60 100644
--- a/src/display/svg.js
+++ b/src/display/svg.js
@@ -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) +