Unity Shader Edge Detection

2024-01-18 23:13 UTC gpt-4 Open in ChatGPT ↗

You

I am making a full-screen shader effect in Unity using shader graph. I want to implement edge-detection on the color buffer. what’s the custom shadergraph code i need to write?

ChatGPT

Creating a full-screen edge-detection effect in Unity using Shader Graph requires you to follow certain steps. Shader Graph is a powerful tool for building shaders visually, so you’ll be able to see the changes in real time. Here’s a basic outline of what you need to do:

1. Create a New Shader Graph:

   • In your Unity project, right-click in the Project window.
   • Go to Create -> Shader -> Image Effect Shader Graph. This will create a new Shader Graph asset for your full-screen effect.

2. Open and Setup Shader Graph:

   • Double-click the newly created Shader Graph asset to open it.
   • You’ll need to set up the main texture input, which will be the color buffer of your screen. Add a Texture 2D property and name it something like “_MainTex”.

3. Implementing Edge Detection:

   • To implement edge detection, you’ll generally use a technique called “Sobel filtering”. This involves sampling the texture around a given pixel and highlighting areas where there is a significant change in color.
   • Create a node to sample the texture at the current UV, and additional nodes to sample the texture at UVs slightly offset in each direction (up, down, left, right).
   • Calculate the color differences between each of these samples and the center sample.
   • Combine these differences to find areas with high contrast (edges).
   • Use a Threshold parameter to control the sensitivity of the edge detection.

4. Adding Parameters for Customization:

   • You might want to expose parameters like Edge Strength, Edge Thickness, and Threshold to allow for easy adjustments in the effect.
   • Create these as properties in the Shader Graph so you can modify them from the material inspector.

5. Output the Result:

   • Combine the calculated edge information with the original texture color, or output it as a black-and-white mask, depending on your desired effect.
   • Connect the final result to the Master Node’s Color slot.

6. Testing the Shader:

   • Create a material from your new shader.
   • Apply this material to a full-screen quad or use it in a post-processing effect.

7. Fine-Tuning:

   • Adjust your parameters and fine-tune the edge detection effect to get the desired visual result.
   • You might need to experiment with the sampling offsets and the way you calculate the color differences to get a smooth and visually pleasing effect.

8. Optimization:

   • Once you’re happy with the result, consider optimizing your shader for performance, especially if it will be used in a real-time application.

Remember, Shader Graph allows you to see the changes in real-time, so you can experiment with different settings and nodes to achieve the desired effect. If you’re not familiar with Sobel filtering or shader programming in general, you might need to look up some tutorials or documentation for more detailed instructions on each step.

You

what’s the sobel code?

ChatGPT

The Sobel operator is used in image processing, particularly within edge detection algorithms. When implementing the Sobel operator in a shader like Unity’s Shader Graph, you’re essentially applying a pair of 3x3 convolution kernels to an image. These kernels are designed to respond maximally to edges running vertically and horizontally relative to the pixel grid, one kernel for each of the two perpendicular orientations.

Here’s a basic representation of the Sobel kernels:

For horizontal edges:

-1  0  1
-2  0  2
-1  0  1

For vertical edges:

-1 -2 -1
 0  0  0
 1  2  1

In Shader Graph, you would implement this by sampling the texture at each of the surrounding 8 pixels around the current pixel, and then multiplying these samples by the corresponding values in the Sobel kernel. The results of these multiplications are then summed up to get the final value for each kernel.

Here’s a simplified version of the code you might write in a shader (note that this is a conceptual representation, as Shader Graph uses a node-based interface):

float3 sobelFilter(Texture2D inputTex, float2 uv, float2 texSize) {
    float2 pixelSize = 1.0 / texSize; // Size of one pixel

    // Sample the texture at different points
    float3 tl = tex2D(inputTex, uv + float2(-pixelSize.x, pixelSize.y)).rgb; // Top-left
    float3 l  = tex2D(inputTex, uv + float2(-pixelSize.x, 0)).rgb;          // Left
    float3 bl = tex2D(inputTex, uv + float2(-pixelSize.x, -pixelSize.y)).rgb;// Bottom-left
    float3 t  = tex2D(inputTex, uv + float2(0, pixelSize.y)).rgb;           // Top
    float3 b  = tex2D(inputTex, uv + float2(0, -pixelSize.y)).rgb;          // Bottom
    float3 tr = tex2D(inputTex, uv + float2(pixelSize.x, pixelSize.y)).rgb;  // Top-right
    float3 r  = tex2D(inputTex, uv + float2(pixelSize.x, 0)).rgb;           // Right
    float3 br = tex2D(inputTex, uv + float2(pixelSize.x, -pixelSize.y)).rgb; // Bottom-right

    // Apply the Sobel kernel
    float3 sobelH = tl + 2 * t + tr - bl - 2 * b - br; // Horizontal edges
    float3 sobelV = tl + 2 * l + bl - tr - 2 * r - br; // Vertical edges

    // Combine the horizontal and vertical results
    float3 edgeStrength = sqrt(sobelH * sobelH + sobelV * sobelV);

    return edgeStrength;
}

In Shader Graph, you would create a similar structure using nodes. Each tex2D call corresponds to a Sample Texture 2D node, and you would use various arithmetic nodes to perform the multiplications and additions.

Remember, the output of this function (edgeStrength) will represent the strength of the edges at each pixel. You can use this value to visualize edges in your image, typically by displaying these values as a grayscale image or using them to modulate some other property of your scene.

You

Ok I want to call this function from within shadergraph

ChatGPT

Calling a custom function like the Sobel filter within Unity’s Shader Graph requires you to use a Custom Function node. This node allows you to inject custom HLSL code into your Shader Graph. To do this for the Sobel edge detection, follow these steps:

1. Write the Custom HLSL Code:

   • First, you need to write the HLSL code for the Sobel filter. You can use the conceptual representation provided earlier as a starting point.
   • Save this code in a .hlsl file within your Unity project’s Assets folder.

2. Create a Shader Graph:

   • If you haven’t already, create a new Shader Graph in Unity.

3. Add the Custom Function Node:

   • Open your Shader Graph and right-click on the graph.
   • Choose Create Node and search for the Custom Function node.
   • Add this node to your graph.

4. Configure the Custom Function Node:

   • Click on the Custom Function node.
   • In the Node settings, you’ll need to specify the file path to your HLSL file and the name of the function you want to call.
   • Set the Type to File and enter the relative path to your HLSL file in the Function field.
   • Enter the name of your Sobel function in the Function Name field.

5. Connect the Inputs and Outputs:

   • The Custom Function node will have slots for inputs and outputs. These should correspond to the parameters of your Sobel function.
   • Connect the appropriate inputs to this node, like the texture you want to apply the edge detection to and any other parameters your function requires.
   • The outputs should be connected to the rest of your Shader Graph nodes to integrate the edge detection effect into your shader.

6. Testing and Adjusting:

   • After setting up the node, you can test the shader by creating a material and applying it to a suitable object in your scene.
   • You may need to adjust your Sobel function or the Shader Graph to get the desired effect.

Remember, the specifics of the HLSL code and the inputs/outputs will depend on your particular implementation and what you want to achieve with your shader. The Custom Function node in Shader Graph is a powerful tool that allows a great deal of flexibility by integrating custom code into the visual node-based system.

You

How must the function be formatted ?

ChatGPT

When you’re using a Custom Function node in Unity’s Shader Graph, your HLSL function must follow a specific format to ensure compatibility. The function needs to clearly define its inputs and outputs, adhering to the requirements of the Shader Graph system. Here’s a guideline on how to format your function:

Basic Structure

The basic structure of your HLSL function should be something like this:

void FunctionName(InputParameters, out OutputParameters)
{
    // Function implementation
}

Example: Sobel Edge Detection Function

For a Sobel edge detection function, you would define it with the necessary inputs and outputs. Let’s make an example:

1. File Name: SobelEdgeDetection.hlsl

2. HLSL Function:

void SobelEdgeDetection(float2 uv : TEXCOORD0,
                        Texture2D InputTexture,
                        SamplerState InputSampler,
                        float2 TextureSize,
                        out float3 EdgeStrength : SV_Target)
{
    float2 pixelSize = 1.0 / TextureSize;

    // Sample the texture at different points
    float3 tl = InputTexture.Sample(InputSampler, uv + float2(-pixelSize.x, pixelSize.y)).rgb;
    // ... (other samples)

    // Apply the Sobel kernel
    float3 sobelH = tl + 2 * t + tr - bl - 2 * b - br; // Horizontal edges
    float3 sobelV = tl + 2 * l + bl - tr - 2 * r - br; // Vertical edges

    // Combine the horizontal and vertical results
    EdgeStrength = sqrt(sobelH * sobelH + sobelV * sobelV);
}

Points to Remember

• Input Parameters: These can be texture coordinates, textures, sampler states, and other data that the function needs to operate. In the example above, uv represents the texture coordinates, InputTexture and InputSampler are used for texture sampling, and TextureSize is used to calculate the pixel size.

• Output Parameters: These are usually marked with out and represent the result of your function. In the Sobel function example, EdgeStrength is the output parameter that holds the result of the edge detection.

• Connecting in Shader Graph: In the Shader Graph, you’ll connect your texture and other inputs to the corresponding input slots of the Custom Function node and use the output for further processing or as a final result.

Integrating into Shader Graph

• Add the Custom Function Node: In your Shader Graph, add a Custom Function node.
• Specify the Function: Link the .hlsl file and write the exact name of the function in the appropriate fields of the Custom Function node.
• Connect Inputs and Outputs: Connect the inputs (like UV coordinates, textures) to the Custom Function node and use its output as needed in your shader.

By following this structure and adapting it to your specific needs, you can integrate custom HLSL code into your Shader Graph workflows effectively.