Sampling Texture in Vertex Shader?

Questions & Answers
1

Hi, I’m trying to sample a texture in a vertex shader, but for some reason I’m always getting 0,0,0,0 back from tex2D.

For debug purposes I’m just forwarding the sampled data through to the pixel shader for display. The input texture is solid light green and can be sampled fine in the pixel shader. For some reason it’s not working from the vertex shader.

My graphics card is an nVidia Quadro FX1500, which claims to support shader model 3.0 (which, I believe, is the minimum version for texture sampling from a vertex shader).

Shader "VSTex"
{
    Properties
    {
        _Tex( "Tex", 2D ) = "white" {}
    }

    SubShader
    {
        Tags
        {
            "Queue"="Transparent"
            "RenderType"="Transparent"
        }

        Pass
        {
            Blend SrcAlpha OneMinusSrcAlpha

            CGPROGRAM
                #pragma target 3.0
                #pragma glsl
                #pragma vertex VS
                #pragma fragment PS

                sampler2D _Tex;

                struct SVSInput
                {
                    float4	vertex : POSITION;
                };

                struct SVSToPS
                {
                    float4	pos : POSITION;
                    float4	color : COLOR;
                };

                SVSToPS VS( SVSInput input )
                {
                    SVSToPS     output;

                    output.pos = mul( UNITY_MATRIX_MVP, float4( input.vertex.xyz, 1.0f ));
                    output.color = tex2D( _Tex, float2( 0.0f, 0.0f ));

                    return output;
                }

                float4 PS( SVSToPS input ) : COLOR
                {
                    return float4( input.color.xyz, 0.5f );
                }
            ENDCG
        }
    }
    Fallback Off
}
2

Just use tex2Dlod to sample vertex texture.