image/gif: don't write superfluous global color table

R=r, nigeltao
CC=golang-dev
https://golang.org/cl/11446043

diff --git a/src/pkg/image/gif/writer.go b/src/pkg/image/gif/writer.go
index 23f8b1b3ad1ff259848379c4d0fe739706236743..645f8340ae9103778b73b8a18f6657e65a6ac237 100644 (file)
--- a/src/pkg/image/gif/writer.go
+++ b/src/pkg/image/gif/writer.go
@@ -52,9 +52,6 @@ type encoder struct {
        err error
        // g is a reference to the data that is being encoded.
        g *GIF
-       // bitsPerPixel is the number of bits required to represent each color
-       // in the image.
-       bitsPerPixel int
        // buf is a scratch buffer. It must be at least 768 so we can write the color map.
        buf [1024]byte
 }
@@ -118,23 +115,19 @@ func (e *encoder) writeHeader() {
                return
        }
 
-       // TODO: This bases the global color table on the first image
-       // only.
        pm := e.g.Image[0]
        // Logical screen width and height.
        writeUint16(e.buf[0:2], uint16(pm.Bounds().Dx()))
        writeUint16(e.buf[2:4], uint16(pm.Bounds().Dy()))
        e.write(e.buf[:4])
 
-       e.bitsPerPixel = log2(len(pm.Palette)) + 1
-       e.buf[0] = 0x80 | ((uint8(e.bitsPerPixel) - 1) << 4) | (uint8(e.bitsPerPixel) - 1)
+       // All frames have a local color table, so a global color table
+       // is not needed.
+       e.buf[0] = 0x00
        e.buf[1] = 0x00 // Background Color Index.
        e.buf[2] = 0x00 // Pixel Aspect Ratio.
        e.write(e.buf[:3])
 
-       // Global Color Table.
-       e.writeColorTable(pm.Palette, e.bitsPerPixel-1)
-
        // Add animation info if necessary.
        if len(e.g.Image) > 1 {
                e.buf[0] = 0x21 // Extension Introducer.
@@ -232,7 +225,7 @@ func (e *encoder) writeImageBlock(pm *image.Paletted, delay int) {
        // Local Color Table.
        e.writeColorTable(pm.Palette, paddedSize)
 
-       litWidth := e.bitsPerPixel
+       litWidth := paddedSize + 1
        if litWidth < 2 {
                litWidth = 2
        }