Correcting affine texture mapping for trapezoids

Unity Engine
1

I needed a stable place to post this package, and I figured this might be interesting to somebody here. It was a fun little challenge for me. Maybe you have a great solution ready to go that accounts for all possible vertex positions? I could go further with it but I’m done for the time being.

1036716–38493–$Affine UV fix.unitypackage (33.1 KB)

2

Hello I got that error when importing your package
would u please share again? I am using Unity 3.5 yet
maybe this is the problem?

1169996--44824--$fatalerrata.jpg

3

I have another problem that I can’t slove

1170135--44832--$Untitled.png
1170135--44832--$Untitled.png1640×900 161 KB

4

No, that’s not the problem, but I don’t know what is. Works fine for me.

Your problem is that you’re on Windows. You’ll have to force Unity into OpenGL mode.

5

Would you please explain more about what you have done in the shader or give me a reference to understand it

specifically the calculations you did

for exmple this statement

gl_FragColor = texture2D(_MainTex, shiftedPosition / width_height);
6

You’d need to look at AffineUVFix.cs, which feeds the necessary data to the shader. The key is that at every pixel, the texture coordinate is the a fraction of the way to both dimensions of the quad.

7

hmm, ya

I have written the Shader in Cg for windows users it could be helpful for some people

here it is

Shader "Custom/Affine UV fix Cg" {
	
	Properties {
	
		_MainTex ("Base (RGB)", 2D) = "white" {}
	}
	
	SubShader {
		
		pass{
		 	CGPROGRAM 
 
 			uniform sampler2D _MainTex;
         	
         	#pragma vertex vert             
         	#pragma fragment frag
            
 
 		struct vertexInput {
			float4 vertex : POSITION;			
			float4 texcoord  : TEXCOORD0;
			float4 texcoord1  : TEXCOORD1;			
		};

		struct vertexOutput {
			float4 pos : SV_POSITION;
			float4 uv  : TEXCOORD0;
			float4 uv2  : TEXCOORD1;			
		};
 
        vertexOutput vert(vertexInput input) 
		{
			vertexOutput output; 
			output.pos = mul(UNITY_MATRIX_MVP,  input.vertex);
			
			output.uv = input.texcoord;
			output.uv2  = input.texcoord1 ;
			
			return output;
		}
 
        float4 frag(vertexOutput input) : COLOR 
		{		
			return  tex2D(_MainTex, float2(input.uv)/float2(input.uv2 ));		
		}
		
         ENDCG // here ends the part in Cg
	} 
	}
	
}
8

Why bother to use float4s for the UVs?

9

because I am very new to shaders, I change it to float2 and it worked

thank you :slight_smile:

10

Would you please replay my pm sir,

thanks in advance

11

someone try to use this package on unity 5?
I tried to import it but does not work.

12

use it

Shader "Custom/Affine UV fix Cg" {
  
    Properties {
  
        _MainTex ("Base (RGB)", 2D) = "white" {}
    }
  
    SubShader {
      
        pass{
            CGPROGRAM

            uniform sampler2D _MainTex;
          
            #pragma vertex vert           
            #pragma fragment frag
          

        struct vertexInput {
            float4 vertex : POSITION;         
            float4 texcoord  : TEXCOORD0;
            float4 texcoord1  : TEXCOORD1;       
        };

        struct vertexOutput {
            float4 pos : SV_POSITION;
            float2 uv  : TEXCOORD0;
            float2 uv2  : TEXCOORD1;         
        };

        vertexOutput vert(vertexInput input)
        {
            vertexOutput output;
            output.pos = mul(UNITY_MATRIX_MVP,  input.vertex);
          
            output.uv = input.texcoord;
            output.uv2  = input.texcoord1 ;
          
            return output;
        }

        float4 frag(vertexOutput input) : COLOR
        {     
            return  tex2D(_MainTex, float2(input.uv)/float2(input.uv2 ));     
        }
      
         ENDCG // here ends the part in Cg
    }
    }
  
}