Practical optimisation

While browsing on Wonderfl to see how my cross product shader was doing I came across someone else's code, the evocatively named "forked from: flash on 2012-3-23". Running it I noticed it was slow: it was not doing much but got slower and used more CPU as it ran. So I decided to look into it.

Radial gradient fill

I first tried using gradient fills (via the beginGradientFill method of the Graphics class) in Bug Tunnel Defense. I wanted to use them for shading along the tunnels but could never get them to work, and eventually did it the long way by drawing a series of differently coloured rectangles. The problem was the createGradientBox Matrix function, which no matter what I passed to it would never return the right matrix for a linear fill.

Quadratic curve through three points

Flash has a couple of curve drawing functions in the Graphics class, curveTo and cubicCurveTo, but they can be difficult to use as they use control points. Control points are points off the curve which the curve tends towards. They are intuitive to use when editing in a graphics app but less useful in code when a curve through a point is needed.

drawCircle is slow

This is something I discovered at the weekend. I already knew that the drawCircle function of the Graphics class is slow, slow enough that you don't want to be using it to draw too many circles at once at runtime. Instead render them into a BitmapData using BitmapData.draw wherever possible.