Mail Archives: djgpp/1998/01/14/15:21:24
Victor jetten writes:
>a) if you look at commands like triangle, quad etc, all functions call
>polygon with 3 edges, 4 edges etc. I agree that this ellegant, but is it
>fast? It seems that this would use a lot of unnecessary overhead. Is
>this so?
Not really, since the triangle and quad functions are very simple
wrappers around the generic polygon routines. I use a very dodgy
assumption about the stack layout to avoid having to copy the parameters
into a new structure, so there is very little overhead in this.
>b) in polygon.c all drawing routines, float or fixed, are converted to
>fixed point in the structure POLYGON_EDGE.
Not quite all. The u, v, and z values for perspective correct texture
mapping are manipulated as floats, the rest as integer or fixed point.
This is very simply because it is faster that way, and minimises the
float->int conversions in the scanline plotters.
It would certainly be possible to make a much faster dedicated triangle
plotter, but that is the nature of library code. Allegro needs to handle
a wide range of possible situations, and there is inevitably some
overhead associated with that...
--
Shawn Hargreaves - shawn AT talula DOT demon DOT co DOT uk - http://www.talula.demon.co.uk/
"Pigs use it for a tambourine" - Frank Zappa
- Raw text -