When I don't access one of my textures, the other texture lookup appears black

Question

I have the following CG pixel shader:

float4 main(
    float2 texCoord : TEXCOORD0,
    float4 position : TEXCOORD2,
    float4 color : COLOR,
    uniform sampler2D texture_sample : TEX1,
    uniform sampler2D stipple_sample : TEX2,
    uniform float camera_target_distance) : COLOR
{
    float4 OUT;

    float2 vpos= position.xy / position.w;

    if (tex2D(stipple_sample, vpos).x > 0.5f)
    {
        discard;
    }

    OUT= tex2D(texture_sample, texCoord) * color;
    return OUT;
}

However, if I comment out/remove the discard, or the first tex2D access using stipple_sample (and the discard), my texture lookup against texture_sample always yields black instead of red/yellow.

Answer 1

Are you sure that you don't pass BLACK as your color?