Sunday, April 24

Brand new Baby Bouncing Triangle

At last cl-ptc (the Lisp software renderer) plots a nice, clean triangle, after weeks of fiddling around with interpolator functions, it's a relief. It's my first ever time as a lisp, so I'm proud to present my first ever bit of Lisp porn..

Lisp gets it right

After playing with lots of different methods of linearly interpolating the edges of triangles (well, 3 - DDA, MAI, & Bressenham) in Lisp, I settled for the straight add the gradient to the minor axis. Madness, I hear you say - not really, because Lisp doesn't represent the result of integer division as a float, but as a pair of integers that represent a ratio, so even doing it this way means I can reserve the FPU for perspective - correct texture mapping the way Intel intended. Obviously, the representation of this ratio is implementation dependent, but I'd really hope that in an implemenation with 32 bit fixnums, the ratio is expressed as a 64 bit fixed point integer..of course it's also probably possible to get LISP to use 16 bit integers for coordinates and 32 bit integers for the ratios, but I haven't got that far into the type sysetem, yet.

Friday, April 15

Lisp Software Renderer, Redux

Of course, it's impossible to leave a challenge I got so close to completing, and so I dust off the Lisp software renderer and return to the fray. I've had to grapple a bit with ASDF and learnt the hard way why upper case file names and lower case package names don't mix. Also, trying to write a tail-recursive Bressenham was interesting..only a few more bugs to wrinkle out and it can hit

Then I can go onto the freenode #lisp channel and get a critique, I hope. 123 notes at an (optimize (speed 3)) sounds like there's still a lot of work ahead..