[whatwg] Any chance for Double Buffering in the <canvas>?

[Ian Hickson]

On Sat, 5 Sep 2009, Marius Gundersen wrote:
>
> I've been playing around with the canvas element, making a 3D engine. It 
> works, but is incredibly slow. Part of the reason is probably that the 
> browser renders the canvas everytime I draw something to it. In a 3D 
> engine, as well as a game engine, the entire canvas is erased and 
> redrawn several times a second, and only at the end of each frame does 
> it need to be rendered to the screen.
> 
> This could be solved with a double buffer, and an explicit redraw() 
> function called at the end of each frame. for example:
> 
> function render(){
>   ctx.clearRect(0, 0, width, height);
>   drawSpaceShip(ctx);
>   for(var i=0; i<spaceInvaders.length; i++){
>     drawSpaceInvader(spaceInvaders[i], ctx);
>   }
>   ctx.repaint();
> }
> 
> Of course this is not always desirable. The context2D could therefore 
> have a flag which turns on and off double buffering. Set to true, the 
> canvas is only redrawn when the repaint function is called, set to 
> false, it will repaint every time the user calls a function that draws 
> to the canvas (drawImage, fillRect, stroke... etc).
> 
> So, to sum up, this is what should be added to the context2D object:
> 
> attribute boolean doubleBuffer; //(default false)
> void repaint(); //repaints the entire canvas. Only used if doubleBuffer is
> true

On Sat, 5 Sep 2009, Robert O'Callahan wrote:
> 
> I assume you have a setTimeout handler (or similar) which renders a 
> complete frame before returning. If so, then in Gecko and I think also 
> in Webkit the canvas will not be drawn to the screen while your script 
> is running, only between frames. So I suspect your performance problem 
> has some other cause.

Based on roc's comments, I haven't added the feature here.

It should be noted that long-term, the right solution for 3D is a 3D API, 
not a library on top of the 2D API.

-- 
Ian Hickson               U+1047E                )\._.,--....,'``.    fL
http://ln.hixie.ch/       U+263A                /,   _.. \   _\  ;`._ ,.
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