How to get mouse input from Camera space to UV Shader Space?

Unity Engine
,
1

Hi, all!

I am interested in converting mouse input to the UV texture space, something like this:

5826685--617623--upload_2020-5-9_12-17-48.png
5826685--617623--upload_2020-5-9_12-17-48.png1198×638 265 KB

My initial strategy was to:

  • Obtain the Vector3 mouse point from screen space to world space, after casting a ray cast onto the object where we want to manipulate
  • Set the value of the Vector3 mouse point (in world space) and send it to the Material’s shader property, titled “MousePoint”
  • Inside the shader, convert the mouse point from World Space to Clip Space. Next, convert the mouse point from clip space to screen space.

Here’s my code:

Shader "Unlit/MouePosShader"
{
    Properties
    {
        _MainTex ("Texture", 2D) = "white" {}
        _mousePoint("mousePoint", Vector) = (0,0,0)
        _dist("dist", float) = 0.02
        _centerPt("CenterPoint", float) = 0.5
    }
    SubShader
    {
        Tags { "RenderType"="Opaque" }
        LOD 100

        Pass
        {
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            // make fog work
            #pragma multi_compile_fog

            #include "UnityCG.cginc"

            struct appdata
            {
                float4 vertex : POSITION;
                float2 uv : TEXCOORD0;
                float3 normal: NORMAL;
            };

            struct v2f
            {
                float2 uv : TEXCOORD0;
                UNITY_FOG_COORDS(1)
                float4 vertex : SV_POSITION;
                float2 mousePos: TEXCOORD0;
            };

            sampler2D _MainTex;
            float4 _MainTex_ST;
            float4 _mousePoint;
            float _dist;
            float _centerPt;
            float2 _mousePointModified;

            v2f vert (appdata v)
            {
                v2f o;
                o.vertex = UnityObjectToClipPos(v.vertex);
                o.uv = TRANSFORM_TEX(v.uv, _MainTex);
                float4 mouseVertex = UnityWorldToClipPos(_mousePoint);
                o.mousePos = ComputeScreenPos(mouseVertex);
                UNITY_TRANSFER_FOG(o,o.vertex);
                return o;
            }

            fixed4 frag(v2f i) : SV_Target
            {
                // sample the texture
                float d = length(i.uv + i.mousePos - float2(0.5,0.5));
                float p = 1. - smoothstep(_dist - (_dist * 0.01),
                    _dist + (_dist * 0.01),
                    dot(d, d) * 4.0);
                fixed4 col = fixed4(p, p, p, 0);
                return col;
            }
            ENDCG
        }
    }
}

The problem I had bumped into was that the mouse point either is not moving, or the proper matrix conversion from mouse point world space to mouse point UV space isn’t taking place. I wanted to get some outside feedback on how to make this matrix transformation work out.

Thanks!

1 Like
2

Any update on this? Found a solution?