This pixel shader shows how to decode the color from a font texture with characters packed into all 4 channels, and each channel using special encoding to store the character with the outline. The texture is also allowed to store full 32bit images for some characters.
// DirectX 9 pixel shader float4 PixScene( float4 color : COLOR0, int4 chnl : TEXCOORD1, float2 tex0 : TEXCOORD0 ) : COLOR0 { float4 pixel = tex2D(g_samScene, tex0); if( dot(vector(1,1,1,1), chnl) ) { float val = dot(pixel, chnl); pixel.rgb = val > 0.5 ? 2*val-1 : 0; pixel.a = val > 0.5 ? 1 : 2*val; } return pixel * color; }
The chnl texture coordinate is a 4D vector that shows which channel the character should be read from. If this is (0,0,0,0) the character is interpreted as a 32 bit image. The texture coordinate can be stored in a UBYTE4 type, so it doesn't require much bandwidth when being sent to the video card.