CODEWITHSUNDEEP
unity-game-engineshaderunityscript
user1021110
user1021110

Reputation: 213

Shader programming in Unity

I am trying to write a shader to read the whole frame, pixel by pixel and after some calculations re-write the pixels. I have looked through some codes but most of them were not relevant. Could you give me some hints on how I can read pixels and write pixels in Unity shader programming?

Upvotes: 1

Views: 3697

Answers (3)

user1021110
user1021110

Reputation: 213

Thank you for your advice. they were really helpful. I finally ended up with this code for my shader. And now, a new problem just comes up.

My solution: To solve my keystone problem, I have adapted the "wearing a glass" idea! it means that I have placed on a plane in front of camera and attached the below shader on it. Then I attached the plane to the camera. The problem right now is that is shader works very well but in my VR setting it does not work because I have several cameras and the scene is distorted in one of them (as I want) but other cameras have a normal scenes. Everything is fine until these two scenes have intersection. In that case I have a disjoint scene (please forgive me if is not a correct word). By the way, I thought that instead of using this shader for a "plane infront of camera" I have to apply it on the camera itself. my shader does not work when I add it to the camera although it works perfectly with the plane object. Could you let me know how can I modify this code to be compatible with camera? I am more than welcome to hear your suggestion and ideas besides of my solution.

Shader "Custom/she1" {
    Properties {
    top("Top", Range(0,2)) = 1
    bottom("Bottom", Range(0,2)) = 1
}
    SubShader {

        // Draw ourselves after all opaque geometry
        Tags { "Queue" = "Transparent" }

        // Grab the screen behind the object into _GrabTexture
        GrabPass { }

        // Render the object with the texture generated above
        Pass {


CGPROGRAM
#pragma debug
#pragma vertex vert
#pragma fragment frag
#pragma target 3.0

            sampler2D _GrabTexture : register(s0);
            float top;
            float bottom;

struct data {

    float4 vertex : POSITION;

    float3 normal : NORMAL;

};



struct v2f {

    float4 position : POSITION;

    float4 screenPos : TEXCOORD0;

};



v2f vert(data i){

    v2f o;

    o.position = mul(UNITY_MATRIX_MVP, i.vertex);

    o.screenPos = o.position;

    return o;

}



half4 frag( v2f i ) : COLOR

{

    float2 screenPos = i.screenPos.xy / i.screenPos.w;
    float _half = (top + bottom) * 0.5;
    float _diff = (bottom - top) * 0.5;
    screenPos.x = screenPos.x * (_half + _diff * screenPos.y);
      screenPos.x = (screenPos.x + 1) * 0.5;
    screenPos.y = 1-(screenPos.y + 1) * 0.5 ;
    half4 sum = half4(0.0h,0.0h,0.0h,0.0h);  
    sum = tex2D( _GrabTexture, screenPos);
    return sum;

}
ENDCG
        }
    }

Fallback Off
}

Upvotes: 0

nwellnhof
nwellnhof

Reputation: 33618

If you have the Pro version of Unity, you can achieve this with image (postprocessing) effects. All you have to do is to implement the OnRenderImage callback on a component of a camera. Then you call Graphics.Blit with a material which has a shader. The shader receives the screen contents as main texture.

Upvotes: 1

Strings
Strings

Reputation: 1683

You need texture buffers the size of your frame. Then you want to render your frame into one of the buffers. Now you need to write a fragment shader that reads one buffers, and writes to the other. Then finally you draw the fragment shader output as a flat object that covers the screen.

In shader programming, you do not work pixel by pixel, you define a function that will be used on a single pixel at a position which is a float from 0 to 1 in all 3 axis (although you will only be using 2). That fragment shader is then run for lots of pixel all in parallel, that's how it does everything more quickly.

I hope that brief explanation is enough to get you started. Unity fragment shaders are written in Cg. Cg is a language which is half way between OpenGL's language GLSL and DirectX language HLSL, as all the high level languages compile into native instructions on the graphics card they are all fairly similar. So there are plenty of Cg samples about, and once you can write Cg, you will have no problem reading HLSL and GLSL.

Upvotes: 0

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