Function R_HeightmapToNormalMap

neo/renderer/Image_program.cpp:73–129

================= R_HeightmapToNormalMap it is not possible to convert a heightmap into a normal map properly without knowing the texture coordinate stretching. We can assume constant and equal ST vectors for walls, but not for characters. ================= */

=================
*/
static void R_HeightmapToNormalMap( byte *data, int width, int height, float scale ) {
	int		i, j;
	byte	*depth;

	scale = scale / 256;

	// copy and convert to grey scale
	j = width * height;
	depth = (byte *)R_StaticAlloc( j );
	for ( i = 0 ; i < j ; i++ ) {
		depth[i] = ( data[i*4] + data[i*4+1] + data[i*4+2] ) / 3;
	}

	idVec3	dir, dir2;
	for ( i = 0 ; i < height ; i++ ) {
		for ( j = 0 ; j < width ; j++ ) {
			int		d1, d2, d3, d4;
			int		a1, a3, a4;

			// FIXME: look at five points?

			// look at three points to estimate the gradient
			a1 = d1 = depth[ ( i * width + j ) ];
			d2 = depth[ ( i * width + ( ( j + 1 ) & ( width - 1 ) ) ) ];
			a3 = d3 = depth[ ( ( ( i + 1 ) & ( height - 1 ) ) * width + j ) ];
			a4 = d4 = depth[ ( ( ( i + 1 ) & ( height - 1 ) ) * width + ( ( j + 1 ) & ( width - 1 ) ) ) ];

			d2 -= d1;
			d3 -= d1;

			dir[0] = -d2 * scale;
			dir[1] = -d3 * scale;
			dir[2] = 1;
			dir.NormalizeFast();

			a1 -= a3;
			a4 -= a3;

			dir2[0] = -a4 * scale;
			dir2[1] = a1 * scale;
			dir2[2] = 1;
			dir2.NormalizeFast();

			dir += dir2;
			dir.NormalizeFast();

			a1 = ( i * width + j ) * 4;
			data[ a1 + 0 ] = (byte)(dir[0] * 127 + 128);
			data[ a1 + 1 ] = (byte)(dir[1] * 127 + 128);
			data[ a1 + 2 ] = (byte)(dir[2] * 127 + 128);
			data[ a1 + 3 ] = 255;
		}
	}


	R_StaticFree( depth );
}