How to draw this effect with any technology on iOS

Hi there, the effect I want to implem开发者_开发百科ent is burning out user's signature. I've done the signature drawing with quartz2D. Can any one show me a direction for drawing the burning glow effect? thanks!

The glow is caused by light streaming from a source through the strokes and illuminating particles in the air as it travels.

So a brute-force solution that works when viewed directly from the front is to draw the plane several times with additive transparency. You'll want to move and scale the plane for each draw so that you're tracing out the shape of a frustum.

You'll need to do so many draws that I can't imagine you'll end up with both real-time performance and an acceptable result. You should be fine if you can spend a second or a half-second or so on preparing the image on e though.

The most obvious alternative would be to work backwards, writing a shader that traces back through the frustum, sampling the 2d texture appropriately. That's likely to cost a similar amount because texture sampling will be the bottleneck due to memory bandwidth (make sure you upload as a one-channel texture in any event), but could be done so as to work from any angle.