869331 - [B2G/SkiaGL] Flickering with mozillaball

Status: RESOLVED FIXED

(Core :: Graphics: Canvas2D, defect)

Description

[Peter Chang[:pchang]]

With B2G/SkiaGL, saw Red ball flicker in mozillaball app

https://github.com/mozilla/openwebapps/tree/develop/examples/mozillaball

Comment 1

[Peter Chang[:pchang]]

Based on bug 843599, it still had flicker by adding fence/waitsync implementation.

Comment 2

[Peter Chang[:pchang]]

Mozillaball app used arc/fill to draw the red ball, as shown below.

context.clearRect(0,0,320,440);                                                               
context.beginPath();
context.fillStyle="#0000ff";                                                                  
// Draws a circle of radius 20 at the coordinates 100,100 on the canvas                             
context.arc(x,y,20,0,Math.PI*2,true);
context.closePath();
context.fill();

And this problem could be solved by calling DrawTargetSkia::Flush() at the end of draw cmds.

Checking the timing of Flush() calls.

Comment 3

[Chiajung Hung [:chiajung]]

Attachment: workaround patch

It seems there are 2 problems:

1. SkCanvas do not flushed correctly
2. Rendered data not read out correctly

Apply this workaround patch then the ball runs without problem.

Comment 4

[Chiajung Hung [:chiajung]]

I am curious why the gfxSurface contain part render result now. That maybe the key for various similar problem.

For this case, you can call mGLContext->PublishFrame before RequestFrame rather than mark out code to fix it, too.

Comment 5

[Chiajung Hung [:chiajung]]

Attachment: workaround patch v2

Better fix to the bug.

As SkiaGL may queue the draw call until flush, we must flush it before trying to access buffer data.

Comment 6

[Chiajung Hung [:chiajung]]

Attachment: Patch v1

SkiaGL default to store draw operations in a queue until flush.
Flush the queue right before present the frame.

Comment 7

[George Wright (:gw280) (needinfo me!)]

Comment on attachment 748897 [details] [diff] [review]
Patch v1

Review of attachment 748897 [details] [diff] [review]:
-----------------------------------------------------------------

You probably don't need to check explicitly against nullptr, but this looks good.

Comment 8

[Chiajung Hung [:chiajung]]

https://tbpl.mozilla.org/?tree=Try&rev=f95e177e1dd0

Comment 9

[Chiajung Hung [:chiajung]]

Attachment: Patch v1

Commitable version, carry r+.

Comment 10

[(PTO June 19-July 7) Ryan VanderMeulen]

https://hg.mozilla.org/projects/birch/rev/31c555ae96f3

Comment 11

[(PTO June 19-July 7) Ryan VanderMeulen]

https://hg.mozilla.org/mozilla-central/rev/31c555ae96f3