code review 4468044: exp/draw: fast paths for drawing a YCbCr or an NRGBA on...

exp/draw: fast paths for drawing a YCbCr or an NRGBA onto an RGBA.

On my laptop, I had an 800x600 jpeg and an 800x600 png (with
transparency). I timed how long it took to draw each image onto an
equivalently sized, zeroed RGBA image.

Previously, the jpeg took 75ms and the png took 70ms, going through
the medium-fast path, i.e. func drawRGBA in draw.go.

After this CL, the jpeg took 14ms, and the png took 21ms with the
Over operator and 12ms with the Src operator.

It's only a rough estimate basd on one image file, but it should
give an idea of the order of magnitude of improvement.

[nigeltao, 2011-05-04 13:31:57]

Hello rsc (cc: adg, golang-dev@googlegroups.com, r),

I'd like you to review this change to
https://go.googlecode.com/hg/

[r, 2011-05-04 16:05:00]

LGTM

http://codereview.appspot.com/4468044/diff/3001/src/pkg/exp/draw/draw.go
File src/pkg/exp/draw/draw.go (right):

http://codereview.appspot.com/4468044/diff/3001/src/pkg/exp/draw/draw.go#newc...
src/pkg/exp/draw/draw.go:71: switch src0 := src.(type) {
you can reuse src, which would also guarantee you don't use the wrong var.
switch src := src.(type)

http://codereview.appspot.com/4468044/diff/3001/src/pkg/exp/draw/draw.go#newc...
src/pkg/exp/draw/draw.go:86: switch src0 := src.(type) {
ditto re src0

[nigeltao, 2011-05-04 16:22:13]

http://codereview.appspot.com/4468044/diff/3001/src/pkg/exp/draw/draw.go
File src/pkg/exp/draw/draw.go (right):

http://codereview.appspot.com/4468044/diff/3001/src/pkg/exp/draw/draw.go#newc...
src/pkg/exp/draw/draw.go:71: switch src0 := src.(type) {
On 2011/05/04 16:05:01, r wrote:
> you can reuse src, which would also guarantee you don't use the wrong var.
> switch src := src.(type)

I prefer src0, to match the dst0 and mask0 variable names.

[nigeltao, 2011-05-04 17:17:58]

*** Submitted as http://code.google.com/p/go/source/detail?r=949313d4c508 ***

exp/draw: fast paths for drawing a YCbCr or an NRGBA onto an RGBA.

On my laptop, I had an 800x600 jpeg and an 800x600 png (with
transparency). I timed how long it took to draw each image onto an
equivalently sized, zeroed RGBA image.

Previously, the jpeg took 75ms and the png took 70ms, going through
the medium-fast path, i.e. func drawRGBA in draw.go.

After this CL, the jpeg took 14ms, and the png took 21ms with the
Over operator and 12ms with the Src operator.

It's only a rough estimate basd on one image file, but it should
give an idea of the order of magnitude of improvement.

R=rsc, r
CC=adg, golang-dev
http://codereview.appspot.com/4468044