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Easy C typecast/SDL problem... - Printable Version

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Easy C typecast/SDL problem... - sealfin - Oct 10, 2003 08:53 AM

I'm just trying to plot one pixel directly to a surface (which has already been locked, et al) with...
Code:
theSurface->pixels[ (( 640 * ( y - 1 )) + x ) ] = SDL_MapRGB( theSurface->format, 255, 0, 0 );
...unfortunately, I just get reported the error "invalid use of void expression" - I've tried to typecast the plot, but this merely changes the error reported - any suggestions?

Easy C typecast/SDL problem... - hams - Oct 10, 2003 09:35 AM

Quote:
Code:
theSurface->pixels[ (( 640 * ( y - 1 )) + x ) ] = SDL_MapRGB( theSurface->format, 255, 0, 0 );
...unfortunately, I just get reported the error "invalid use of void expression" - I've tried to typecast the plot, but this merely changes the error reported - any suggestions?


based on that, it would seem SDL_MapRGB returns void.
check the prototype for SDL_MapRGB.

kevin

Easy C typecast/SDL problem... - sealfin - Oct 10, 2003 10:04 AM

No, the pixels member of SDL_Surface is the void pointer - which is where the plot/assignment falls apart...

Easy C typecast/SDL problem... - hams - Oct 10, 2003 12:06 PM

if pixels is void* then you have to cast it first.

int *pix_ptr = theSurface->pixels;

pix_ptr[ blah] = SDL_MapRGB (...)

Easy C typecast/SDL problem... - sealfin - Oct 10, 2003 12:39 PM

Thanks, I'd completely overlooked that... Blush Thanks!