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Comment by pcwalton | Hacker News Reader

One of the coolest things I learned from the original blog post [1] on Ejecta was a trick that the library uses for drawing polygons on the GPU in OpenGL without triangulating them first [2]. It's one of the coolest graphics programming tricks I've ever seen and when I understood how it worked my mind was blown.

[1]: http://phoboslab.org/log/2012/09/ejecta

[2]: http://www.glprogramming.com/red/chapter14.html#name13

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With a bit more trickery, you can even implement the Non-Zero fill rule (Canvas2D default), instead of the simpler Even-Odd rule. Ejecta now supports both:

https://github.com/phoboslab/Ejecta/blob/master/Source/Eject...

Could I also use this technique to clip a scene to the path of a complex polygon?

How does it hold up with many overlapping shapes of varying color; wouldn't it lead to far more state changes and ultimately much greater fill-rate?

And what are your thoughts on using this for font rendering?

This looks brilliant. Thanks for the info.

this is impressive!

btw do you have any numbers on how bezie drawing using OpenGL compares to regular drawing on 2d canvas, performance wise?

let's say I have an html5 app which draws stuff using 2d canvas. do you think it makes sense to draw to webgl instead using implementation like yours, i.e. mapping 2d canvas api to webgl?

Using stencil buffer to draw polygons without tesselation seems to be one of those folklores that is not widely known. I learned about it some years ago here:

http://zrusin.blogspot.com/2006/07/hardware-accelerated-poly...

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