1087863 - Use clip rects to restrict area that blend modes apply to

Status: RESOLVED INCOMPLETE

(Firefox Graveyard :: Shumway, defect, P1)

Description

[Michael Bebenita [:mbx]]

Attachment: copy.html

The destination-in blend mode is necessary to perform masking operations and is extremely slow in Canvas 2D. This is happening on both cg and skia. (It is a lot faster in skia if hardware acceleration is enabled.)

In the attached test case, click "Blend Destination-In" and compare that with "Blend Normal". Chrome is about 20x faster than Firefox.

Comment 1

[Michael Bebenita [:mbx]]

Looks like it's highly dependent on the size of the destination canvas:

Canvas
 Size
 
 272    4235.77 Op/s. 	
 288    3964.51 Op/s. 	
 304    3712.44 Op/s. 	
 320    3499.25 Op/s. 	
 336    3155.50 Op/s. 	
 352    3060.90 Op/s. 	
 368    2337.76 Op/s. 	
 384    2616.64 Op/s. 	
 400    2523.93 Op/s. 	
 416    2343.32 Op/s. 	
 432    2141.08 Op/s. 	
 448    2070.86 Op/s. 	
 464    1928.59 Op/s. 	
 480    1826.05 Op/s. 	
 496    1735.63 Op/s. 	// There's an interesting spike here.
 512    787.29 Op/s. 	
 528    775.89 Op/s. 	
 544    794.76 Op/s. 	
 560    708.13 Op/s. 	
 576    714.09 Op/s. 	
 592    637.03 Op/s. 	
 608    613.41 Op/s. 	
 624    568.76 Op/s. 	
 640    466.16 Op/s. 	
 656    526.14 Op/s. 	
 672    520.99 Op/s. 	
 688    485.88 Op/s. 	
 704    480.86 Op/s. 	
 720    440.36 Op/s. 	
 736    434.81 Op/s. 	
 752    391.43 Op/s. 	
 768    379.30 Op/s. 	
 784    366.19 Op/s. 	
 800    343.73 Op/s. 	
 816    338.45 Op/s. 	
 832    331.79 Op/s. 	
 848    311.56 Op/s. 	
 864    309.31 Op/s. 	
 880    298.01 Op/s. 	
 896    286.89 Op/s. 	
 912    273.57 Op/s. 	
 944    251.94 Op/s. 	
 960    245.26 Op/s. 	
 976    207.67 Op/s. 	
 992    232.02 Op/s. 	
1008    220.63 Op/s. 	
1024    216.49 Op/s. 	
1040    208.22 Op/s. 	
1056    204.39 Op/s. 	
1072    201.92 Op/s. 	
1088    198.23 Op/s. 	
1104    189.14 Op/s. 	

One question is, what is it about destination-in that requires a read back?

Comment 2

[Michael Bebenita [:mbx]]

Attachment: blend-chart.png

Blend operations copying a 64x64 pixel rectangle to a destination canvas of varying size 256, 512, 1024 and 2048.

Comment 3

[Markus Stange [:mstange]]

Operator destination-in affects all pixels in the target canvas, even if you only draw a small rect. If you want to contain the effects of drawImage to the rect that you're drawing, you need to set a clip first.

Comment 4

[Michael Bebenita [:mbx]]

I see, that makes a lot of sense.

Comment 5

[Till Schneidereit [:till]]

See comment 3.