tex.Load invalid call

Unity Engine
,
1

I’m adapting the default Unity UI shader and want to use tex.Load to get a specific pixel. Simply saying someTex.Load(x,y,z) doesn’t work and I don’t quite understand why.

Here’s what I’ve got:

Shader "UI/TexLoad Wrong"
{
    Properties
    {
        [PerRendererData] _MainTex ("Main", 2D) = "white" {}
        _ColorScheme ("Color Scheme", 2D) = "white" {}

        _StencilComp ("Stencil Comparison", Float) = 8
        _Stencil ("Stencil ID", Float) = 0
        _StencilOp ("Stencil Operation", Float) = 0
        _StencilWriteMask ("Stencil Write Mask", Float) = 255
        _StencilReadMask ("Stencil Read Mask", Float) = 255

        _ColorMask ("Color Mask", Float) = 15

        [Toggle(UNITY_UI_ALPHACLIP)] _UseUIAlphaClip ("Use Alpha Clip", Float) = 0
        // do noise
    }

    SubShader
    {
        Tags
        {
            "Queue"="Transparent"
            "IgnoreProjector"="True"
            "RenderType"="Transparent"
            "PreviewType"="Plane"
            "CanUseSpriteAtlas"="True"
        }

        Stencil
        {
            Ref [_Stencil]
            Comp [_StencilComp]
            Pass [_StencilOp]
            ReadMask [_StencilReadMask]
            WriteMask [_StencilWriteMask]
        }

        Cull Off
        Lighting Off
        ZWrite Off
        ZTest [unity_GUIZTestMode]
        Blend SrcAlpha OneMinusSrcAlpha
        ColorMask [_ColorMask]

        Pass
        {
            Name "Default"
        CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #pragma target 2.0

            #include "UnityCG.cginc"
            #include "UnityUI.cginc"

            #pragma multi_compile_local _ UNITY_UI_CLIP_RECT
            #pragma multi_compile_local _ UNITY_UI_ALPHACLIP

            struct appdata_t
            {
                float4 vertex   : POSITION;
                float4 color    : COLOR;
                float2 texcoord : TEXCOORD0;
                UNITY_VERTEX_INPUT_INSTANCE_ID
            };

            struct v2f
            {
                float4 vertex   : SV_POSITION;
                fixed4 color    : COLOR;
                float2 texcoord  : TEXCOORD0;
                float4  worldPos    : TEXCOORD1;
                float4  somePixel    : TEXCOORD2;
                UNITY_VERTEX_OUTPUT_STEREO
            };


            sampler2D _ColorScheme;
            sampler2D _MainTex;
            fixed4 _TextureSampleAdd;
            float4 _ClipRect;
            float4 _MainTex_ST;

            v2f vert(appdata_t v)
            {
                v2f o;
                UNITY_SETUP_INSTANCE_ID(v);
                UNITY_INITIALIZE_VERTEX_OUTPUT_STEREO(o);
                o.worldPos = v.vertex;
                o.vertex = UnityObjectToClipPos(o.worldPos);
                o.texcoord = TRANSFORM_TEX(v.texcoord, _MainTex);
                o.color = v.color;

                // *** LOAD THE CORRECT PIXEL
                int x = 1; // get this
                int y = 1; // get that
                o.somePixel = _ColorScheme.Load(int3(x, y, 0)); // THIS IS WRONG!
                return o;
            }

            fixed4 frag(v2f i) : SV_Target
            {
                half4 main = (tex2D(_MainTex, i.texcoord) + _TextureSampleAdd);
            
                // TODO apply somePixel

                #ifdef UNITY_UI_CLIP_RECT
                color.a *= UnityGet2DClipping(i.worldPos.xy, _ClipRect);
                #endif

                #ifdef UNITY_UI_ALPHACLIP
                clip (color.a - 0.001);
                #endif

                return color;
            }
        ENDCG
        }
    }
}

The issue is #80 ( sampler2D _ColorScheme; ) combined with line #99 ( o.somePixel = _ColorScheme.Load(int3(x, y, 0)); ).

In another shader, I could use TEXTURE2D(_ColorScheme); then could call _ColorScheme.Load(x,y,z) but that’s no good here, so I’m wondering what I need to do to access the texture in this context to be able to use tex.Load.

2

I finally found the docs for this: Unity - Manual: Using sampler states See “Separate textures and samplers.”

I didn’t know how to separate the sampler from the texture and how to access the texture itself, rather than by way of the sampler since when using tex.Load the sampler is unneeded.

Still not 100% on the difference between the various macros that are available.

3

Sampler2D _tex; & tex2D(_tex, uv) are D3D9 style HLSL. The texture and the sampler state are a single object.

Texture2D _tex; SamplerState sampler_tex; and _tex.Sample(sampler_tex, UV) are the equivalent D3D11 HLSL.

Most of the texture related macros Unity has are to hide that difference and switch between the two styles for platforms that don’t support the separate texture and sampler state. Like OpenGLES.

1 Like