Over on Gasman‘s blog he’s put up an interesting post about his second-place 256b Intro, “Nrrr-ka-rrrk“. If you’ve not seen the Intro I encourage you to download it and at least view it in a ZX emulator – it’s an odd, erratic, almost “techno” production. The blog entry details the design process of the intro (if you can call accidental music a “design process”), and may be interesting if you’re of a technical bent.
He also covers a little information about the technical aspects of writing a roto-zoomer (well, the roto part of it). The process is actually quite simple, as he says – start at a point and for each screen position you want to draw, step through a texture or image at steps of sin θ down and cos θ across. This approach provides you with the position in the image which should be copied to the screen. I used the same technique in my part for the “Bunch Of Arse” demo. However, I also included an additional option – rather than stepping through the image using a straight sin θ, cos θ calculation (actually stored in tables), the cos θ was stepped quicker (or in some points in reverse, I recall). Stepping through the sin and cos tables at different speeds gives the warping effect. It can look nice (I think my BOA part could have been improved had I not tried to “blur” the ATTR values), and at little expense to size or speed.
Hmm. I really should get a move on with democode.org.