Bug 49719

Summary:

Qt should handle unmultiplied RGBA pixel arrays

Product:

WebKit

Reporter:

Zoltan Herczeg <zherczeg>

Component:

SVG

Assignee:

Nobody <webkit-unassigned>

Status:

RESOLVED WONTFIX

Severity:

Normal

CC:

benjamin, hausmann, kbalazs, kling, mdelaney7, zimmermann

Priority:

Version:

528+ (Nightly build)

Hardware:

OS:

OS X 10.5

Attachments:

Description	Flags
patch	benjamin: review-

Zoltan Herczeg

Reported 2010-11-18 01:57:53 PST

This is just a quick patch. Let Qt decide when it needs a unmultiplied / multiplied conversion, and do it in an effective way.

Attachments
patch (6.90 KB, patch) 2010-11-18 02:03 PST, Zoltan Herczeg	benjamin: review-	Details Formatted Diff Diff
View All Add attachment proposed patch, testcase, etc.

Zoltan Herczeg

Comment 1 2010-11-18 02:03:29 PST

Created attachment 74217 [details] patch

Andreas Kling

Comment 2 2010-11-18 02:13:20 PST

Comment on attachment 74217 [details] patch The reason we're not doing this is because when using the "raster" graphics system, convertToFormat(ARGB32_PM) is a no-op. With that in mind, combining the RGB<->BGR and premultiplication into a single pass over the image is faster than anything Qt can do. This patch will regress performance, so is there any other reason to do this besides code cleanliness?

Zoltan Herczeg

Comment 3 2010-11-18 02:16:24 PST

I thought Qt may have an optimized assembly routine to convert the data, this is surprising. And what about non-raster modes?

Benjamin Poulain

Comment 4 2010-11-18 02:23:42 PST

Comment on attachment 74217 [details] patch This patch basically revert all the optimizations done recently by Andreas. You can add a ABGR format to QImage to optimize this further.

Balazs Kelemen

Comment 5 2010-11-18 02:35:40 PST

(In reply to comment #3) > I thought Qt may have an optimized assembly routine to convert the data, this is surprising. And what about non-raster modes? I think Qt has this for RGB -> RGB_PM, but not for RGB -> BGR_PM what we need there.

Benjamin Poulain

Comment 6 2010-11-18 02:48:23 PST

(In reply to comment #5) > I think Qt has this for RGB -> RGB_PM, but not for RGB -> BGR_PM what we need > there. That is why Andreas made those changes. CPU cache is more important than raw CPU power for those kind of basic conversion. By doing it at once instead of in two passes, you gain a lot of performance. To go further, you could implement this one pass conversion with SIMD, this should ideally be done in QtGui.

Benjamin Poulain

Comment 7 2010-11-19 06:59:00 PST

Closing the bug, we can reopen if you come with a better implementation.

Balazs Kelemen

Comment 8 2010-11-19 10:26:36 PST

As I heard from Zoltan the one pass approach hurts performance in SVG when you usually need the unmultiplied data, but this should be explained by him :)

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