How would I program this shader?

Unity Engine
1

So what I want to do is, a shader where each triangle has a texture inside of it.

3017616--225333--upload_2017-4-3_13-22-5.png
3017616--225333--upload_2017-4-3_13-22-5.png856×446 10.4 KB

So what I was thinking of doing was, somehow using the vertices positions, to get x-y coordinates to sample the texture.

Something like this:
3017616--225335--upload_2017-4-3_13-26-54.png

2

Your plan will work. You can make UV’s out of anything and then supply them in your tex2D(blahblah, myCustomUVs) sample.

World position, screen position, etc are all fair game.

3

So here I have a really basic sprite shader, that I think I could use as a base for what I want.

I chose a sprite shader as a base, because well my game is in 2d, and pretty much everything I have in the game is a sprite ( so my guess is, this will avoid some depth-transparency issues etc).

I also commented out some of the code that this shader wont use it.

Shader "Unlit/Celestial-Body"
{
    Properties
    {
        _MainTex ("Texture", 2D) = "white" {}
    }
    
SubShader {
        Tags{
        "Queue" = "Transparent"
        "IgnoreProjector" = "True"
        "RenderType" = "Transparent"
        "PreviewType" = "Plane"
        "CanUseSpriteAtlas" = "True"
    }

        Cull Off
        Lighting Off
        ZWrite Off
        Blend One OneMinusSrcAlpha

        Pass{
        CGPROGRAM
#pragma vertex vert
#pragma fragment frag
#pragma target 2.0
#pragma multi_compile _ ETC1_EXTERNAL_ALPHA
#include "UnityCG.cginc"

    struct appdata_t {
        float4 vertex   : POSITION;
        //float4 color    : COLOR; I wont use color ( for now atleast)
        float2 texcoord : TEXCOORD0;
        UNITY_VERTEX_INPUT_INSTANCE_ID
    };

    struct v2f {
        float4 vertex   : SV_POSITION;
        //fixed4 color : COLOR; I wont use color ( for now atleast)
        float2 texcoord  : TEXCOORD0;
        UNITY_VERTEX_OUTPUT_STEREO
    };

    fixed4 _Color;

    v2f vert(appdata_t IN) {
        v2f OUT;
        UNITY_SETUP_INSTANCE_ID(IN);
        UNITY_INITIALIZE_VERTEX_OUTPUT_STEREO(OUT);
        OUT.vertex = UnityObjectToClipPos(IN.vertex);
        OUT.texcoord = IN.texcoord;
        //OUT.color = IN.color * _Color; I wont use color ( for now atleast)

        return OUT;
    }

    sampler2D _MainTex;

    fixed4 SampleSpriteTexture(float2 uv)
    {
        fixed4 color = tex2D(_MainTex, uv);

        // Removed the alpha thing, because I wont use transparency in this shader

        return color;
    }

    fixed4 frag(v2f IN) : SV_Target{
        fixed4 c = SampleSpriteTexture(IN.texcoord);// *IN.color; I wont use color ( for now atleast)

        //c.rgb *= c.a; // This shader wont use transparency so I dont use alpha

        return c;
    }
        ENDCG
    }
    }
}

Now what I would need to figure out is, how to get the texture coordinates from the triangles…

4

If your triangles object-space vertex positions are normal to their center (xy ranging from -0.5 to 0.5 with the origin at the center), then you can just shift them into UV space and pass them to your fragment shader.

// shift object-space positions to (0-1) UV coordinates
OUT.texcoord = IN.vertex.xy + 0.5;

If your range differs, perhaps -1 to 1 then you’ll need to scale them to the normalized range. In this case, you’d divide them by 2.

 // scale and shift object-space positions to (0-1) UV coordinates
OUT.texcoord = IN.vertex.xy * 0.5 + 0.5;