Adding Transparency and Alpha Clipping

Control surface visibility and create complex cut-out effects by manipulating alpha channels and clipping thresholds within the shader graph.

In this lesson, you will learn how to manipulate the alpha channel in Shader Graph to create complex surface visibility and hard-edged cut-out effects.

Understanding Alpha Modes

To control how a surface interacts with light and depth, we first set the Surface Type in the Graph Settings.

Transparent: Uses alpha blending, where the shader calculates the color based on the alpha value. This is perfect for glass or smoke.
Opaque: Uses Alpha Clipping, which forces the GPU to either draw a pixel or discard it entirely based on a threshold.

Implementing Alpha Clipping

Alpha clipping is the secret to creating perforated surfaces like chain-link fences, foliage, or dissolving objects without the high performance cost of traditional transparency. In Shader Graph, you manipulate this by piping a texture or noise map into the Alpha and AlphaClipThreshold inputs on the Master Stack.

If your texture has a value below the AlphaClipThreshold, the pixel is discarded (clipped). You can create a "dissolve" effect by feeding a Simple Noise node into a Subtract node, and plugging that into the AlphaClipThreshold input. By animating a scalar property through the Subtract node, you effectively "burn away" the material pixel-by-pixel.

Practical Implementation

To set this up, ensure your material has Alpha Clipping enabled in the Graph Settings. Use a Sample Texture 2D node and connect the Alpha output to the Alpha slot of your Master Stack. If you want a hard edge, connect that same output to the AlphaClipThreshold slot.

// Conceptually, the GPU logic follows this check:
if (AlphaValue < AlphaClipThreshold) 
{
    discard; // Pixel is not rendered
}

This method is highly efficient for performance because the GPU can perform "Early Z-testing," skipping expensive lighting calculations for pixels that are destined to be clipped. By adjusting the AlphaClipThreshold dynamically via script (using material.SetFloat("_AlphaClip", value)), you can trigger smooth transitions or interactive damage states.

Key Takeaway: Alpha Clipping allows for high-performance visual complexity by discarding pixels based on a threshold, while Transparent mode handles soft blending for objects that require a spectrum of visibility.