// generates a PPM file with an RGB cube pattern for Povray's "cube" mapping

#include <cstdio>
#include <cstdint>

const unsigned CellSize = 512;
const unsigned Width    = CellSize*4;
const unsigned Height   = CellSize*3;

int main()
{
	printf("P6\n%u %u 255\n", Width, Height);
	uint8_t r,g,b;
	
	for(unsigned y=0; y<Height; ++y)
	{
		fprintf(stderr, "%u/%u   \r", y, Height);
		for(unsigned x=0; x<Width; ++x)
		{
			// 4 x 3 cells:
			//
			//  +---+---+---+---+
			//  | 0 | 1 | 2 | 3 |
			//  +---+---+---+---+
			//  | 4 | 5 | 6 | 7 |
			//  +---+---+---+---+
			//  | 8 | 9 |10 |11 |
			//  +---+---+---+---+
			const unsigned cell = (x/CellSize) + (y/CellSize)*4;
			const unsigned cx = x % CellSize;
			const unsigned cy = y % CellSize;
			bool make_grid = true;
			switch(cell)
			{
				case 1: { r = 255*cx/CellSize; g = 255; b = 255*cy/CellSize; break; }
				case 4: { r = 0; g = 255 - 255*cy/CellSize; b = 255*cx/CellSize ; break; }
				case 5: { r = 255*cx/CellSize ; g = 255 - 255*cy/CellSize; b = 255; break; }
				case 6: { r = 255; g = 255 - 255*cy/CellSize;b = 255 - 255*cx/CellSize; break; }
				case 7: { r = 255 - 255*cx/CellSize; g = 255 - 255*cy/CellSize; b = 0; break; }
				case 9: { r = 255*cx/CellSize; g = 0; b = 255 - 255*cy/CellSize; break;}
				default: { const int q = (x+y)/64; r = g = (q%2 ? 255 : 0); b = 0; make_grid = false; break; }
			}
		
			if(make_grid && (x % 16 ==0 || y%16==0 || (x+1)%128<3 || (y+1)%128<3) )
			{
				r = g = b = 0;
			}
			
			putchar(r);
			putchar(g);
			putchar(b);
		}
	}
}