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image/jpeg: rename some internal variables. 

LGTM=dsymonds
R=dsymonds
CC=golang-codereviews
https://golang.org/cl/120980043
This commit is contained in:
Nigel Tao 2014-07-31 17:34:48 +10:00
parent 5a008acec1
commit 17992f7a06
1 changed files with 16 additions and 17 deletions
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33
src/pkg/image/jpeg/scan.go
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@ -123,12 +123,11 @@ func (d *decoder) processSOS(n int) error {
// b is the decoded coefficients, in natural (not zig-zag) order.
b block
dc [nColorComponent]int32
// mx0 and my0 are the location of the current (in terms of 8x8 blocks).
// bx and by are the location of the current (in terms of 8x8 blocks).
// For example, with 4:2:0 chroma subsampling, the block whose top left
// pixel co-ordinates are (16, 8) is the third block in the first row:
// mx0 is 2 and my0 is 0, even though the pixel is in the second MCU.
// TODO(nigeltao): rename mx0 and my0 to bx and by?
mx0, my0 int
// bx is 2 and by is 0, even though the pixel is in the second MCU.
bx, by int
blockCount int
)
for my := 0; my < myy; my++ {
@ -163,26 +162,26 @@ func (d *decoder) processSOS(n int) error {
// 0 1 2
// 3 4 5
if nComp != 1 {
mx0, my0 = d.comp[compIndex].h*mx, d.comp[compIndex].v*my
bx, by = d.comp[compIndex].h*mx, d.comp[compIndex].v*my
if h0 == 1 {
my0 += j
by += j
} else {
mx0 += j % 2
my0 += j / 2
bx += j % 2
by += j / 2
}
} else {
q := mxx * d.comp[compIndex].h
mx0 = blockCount % q
my0 = blockCount / q
bx = blockCount % q
by = blockCount / q
blockCount++
if mx0*8 >= d.width || my0*8 >= d.height {
if bx*8 >= d.width || by*8 >= d.height {
continue
}
}
// Load the previous partially decoded coefficients, if applicable.
if d.progressive {
b = d.progCoeffs[compIndex][my0*mxx*d.comp[compIndex].h+mx0]
b = d.progCoeffs[compIndex][by*mxx*d.comp[compIndex].h+bx]
} else {
b = block{}
}
@ -255,7 +254,7 @@ func (d *decoder) processSOS(n int) error {
if d.progressive {
if zigEnd != blockSize-1 || al != 0 {
// We haven't completely decoded this 8x8 block. Save the coefficients.
d.progCoeffs[compIndex][my0*mxx*d.comp[compIndex].h+mx0] = b
d.progCoeffs[compIndex][by*mxx*d.comp[compIndex].h+bx] = b
// At this point, we could execute the rest of the loop body to dequantize and
// perform the inverse DCT, to save early stages of a progressive image to the
// *image.YCbCr buffers (the whole point of progressive encoding), but in Go,
@ -272,15 +271,15 @@ func (d *decoder) processSOS(n int) error {
idct(&b)
dst, stride := []byte(nil), 0
if d.nComp == nGrayComponent {
dst, stride = d.img1.Pix[8*(my0*d.img1.Stride+mx0):], d.img1.Stride
dst, stride = d.img1.Pix[8*(by*d.img1.Stride+bx):], d.img1.Stride
} else {
switch compIndex {
case 0:
dst, stride = d.img3.Y[8*(my0*d.img3.YStride+mx0):], d.img3.YStride
dst, stride = d.img3.Y[8*(by*d.img3.YStride+bx):], d.img3.YStride
case 1:
dst, stride = d.img3.Cb[8*(my0*d.img3.CStride+mx0):], d.img3.CStride
dst, stride = d.img3.Cb[8*(by*d.img3.CStride+bx):], d.img3.CStride
case 2:
dst, stride = d.img3.Cr[8*(my0*d.img3.CStride+mx0):], d.img3.CStride
dst, stride = d.img3.Cr[8*(by*d.img3.CStride+bx):], d.img3.CStride
default:
return UnsupportedError("too many components")
}