Re: [Algorithms] Draw & fill regular polygon?

[Richard F. <ra...@gm...>]

On 10 August 2011 12:49, Joel B <one...@ea...> wrote:
> I should know how to do this, but i don't. I only have the ability in my system to draw lines (x1,y1,x2,y2)' to a bitmap, or write to the bitmap as a byte array. Can someone tell me the stepwise procedure to draw a polygon of n sides and then fill it? Having trouble finding anything online that doesn't use pre-existing primitives or libraries.
>
> Thanks,
>
> Joel

if you already have a line drawing function, then use the code from
that to update a pair of arrays of min/max on the x axis:

int xmin[SCREEN_HEIGHT] = { SCREEN_WIDTH... }
int xmax[SCREEN_HEIGHT] = { -1... }

then for each step of your line drawing function update the min/max:

replace your: put_pixel(x,y,colour)
with: xmin[y] = min(x,xmin[y]); xmax[y] = max(x,xmax[y]);

Once you have the arrays, it's a simple case of iterating over them
and rendering all pixels between the min and max where the difference
is positive.

foreach y in SCREEN_HEIGHT:
  if( xmax[y] > xmin[y] )
    foreach( x in range( xmin[y], xmax[y] ):
      put_pixel( x,y, colour )

and you have an untextured triangle.
if you want it textured, don't forget to store only UV values when the
max/min is updated.

-- 
fabs();
Just because the world is full of people that think just like you,
doesn't mean the other ones can't be right.