Re: Integration of HTM

On Feb 8, 2010, at 5:18 PM, Robert O'Callahan wrote:

> On Tue, Feb 9, 2010 at 1:25 PM, Maciej Stachowiak <mjs@apple.com> wrote:
> I am concerned however about overlaying the canvas with 0.01 opacity divs. I expect this will have a negative impact on canvas rendering performance, especially if there are significant animations. Because even though 0.01 opacity likely won't draw anything visible, the browser still has to render and composite the content on top of the canvas.
>  
> In the future we can probably expect most browsers to use graphics hardware in a way that makes the compositing cheap/free. However, opacity:epsilon does seem rather ugly. Wouldn't opacity:0 work here? In Gecko at least that would optimize away almost all rendering (while still catching events).
> 
> I am also wondering how this technique can be extended to control target areas that are not rectangles.
> 
> I'm wondering that too. I wonder if it would make sense to add some kind of canvas API that lets you associate an element with the current path. Mmm, sounds like image maps :-).

If we're adding API, then we may as well use the nested subtree approach instead of the overlay approach. I think the main technical advantage of the overlay approach is that it works with no changes to current-generation browsers.

Regards,
Maciej