Proposal an attribute for Canvas element

bug # is 23773,23774



Example:

   <canvas id="myCanvas" imagecanvas="true”></canvas>
    if imagecanvas is true, canvas only render image, otherwise operate like normal case.

Reason:

   During development of browser, we find that,if the browser engine can know that this canvas is only for drawring image and identify this scenario, then the browser engine can give GPU accelaration for this only-drawing-image scenario.

   If we draw canvas, when drawimage,and there are other non-image drawing,like text or line, the performance is downgraded.

   After we implement this attribute for canvas element in our android webkit kernal,we got test data for using this attribute, and not using this attribute.Below is the performance comparision.We use 5 games to test our implementation, and find the effect is obvious,please find detailed data below.


Benefit:

   1) for developer, this attribute is easy to use,we can draw different type draw in different canvas,we can get high performance web page.
   2) for browser engine, it can fully optimize the performance of drawing an image,make best use of powser of GPU accelerator.


Test Data:

1、 FishIE Scenario（http://ie.microsoft.com/testdrive/Performance/FishIETank/Default.html）

number of fish         1 10 20 50 100
before（fps）           46 26 15 12 8
after（fps）            60 58 58 58 50
effect(%）     30.43 123.07 286.66 383.33 525.00
2、 GUIMark3（http://www.craftymind.com/factory/guimark3/bitmap/GM3_JS_Bitmap.html）


before fps） 32
after （fps） 60
effect（%） 87.50
3、 FishBowl Scenario（http://ie.microsoft.com/testdrive/Performance/FishBowl/）

number of fish          5 10 50
before(fps）         5 4 2
after( fps）         60 60 53
effect（%）     1100.00 1400.00 2500.00
4 CanvasGameTest
        fps
before         42
after         121
effect（%） 188.50

5 fishjoy

  fps
before   30fps
after   50fps
effect（%）66.67