27. Introduction to Shader programming

Shader programming is a fascinating and essential aspect of modern game development, especially when working with a powerful engine like Unity. Shaders are small programs that run on the GPU and determine how the graphics are rendered in a game. They are responsible for rendering effects, lighting, shadows, and other visual phenomena that bring a game world to life. Understanding shaders is crucial for any game developer looking to create visually stunning games across multiple platforms.

In Unity, shaders are written using a language called ShaderLab, which is a Unity-specific language, and HLSL (High-Level Shader Language), which is similar to C#. ShaderLab is used to define the properties and subshaders, while HLSL is used to write the actual shader code. Unity provides several built-in shaders, but to fully leverage the power of the engine, learning to write custom shaders is invaluable.

Understanding the Basics of Shaders

At its core, a shader is a program that tells the GPU how to draw something on the screen. There are different types of shaders, each serving a specific purpose:

• Vertex Shaders: These process each vertex's data, such as position, color, and texture coordinates. They are responsible for transforming 3D coordinates into 2D coordinates that can be displayed on the screen.
• Fragment (or Pixel) Shaders: These determine the color of each pixel. They take the output of the vertex shader and compute the color and other attributes of each pixel.
• Geometry Shaders: These can generate additional geometry on the fly. They are not as commonly used as vertex or fragment shaders but can be powerful for certain effects.

Unity's shader system is built around the concept of materials. A material in Unity is an asset that holds a shader and the properties that are used to configure that shader. When you apply a material to a 3D model, the shader attached to that material determines how the model will be rendered.

Creating Your First Shader

To create a simple shader in Unity, follow these steps:

1. In the Project window, right-click and select Create > Shader > Unlit Shader. This will create a new shader file.
2. Open the shader file in a text editor. You will see a template that Unity has generated for you.
3. Modify the shader code to customize its behavior. For instance, you can change the color output in the fragment shader to create a simple color effect.

Here is an example of a simple shader that colors an object red:

Shader "Custom/RedShader" {
    SubShader {
        Pass {
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            
            float4 vert(float4 pos : POSITION) : SV_POSITION {
                return UnityObjectToClipPos(pos);
            }
            
            float4 frag() : SV_Target {
                return float4(1, 0, 0, 1); // Red color
            }
            ENDCG
        }
    }
}

This shader consists of a SubShader block, which contains a Pass block. The CGPROGRAM block contains the actual shader code, with a vertex and fragment function. The vertex function, vert, transforms the vertex position, while the fragment function, frag, returns a red color for each pixel.

Exploring Shader Properties

Shaders can be made more dynamic by using properties. Properties allow you to expose variables in the shader that can be modified in the Unity Editor. This is how you can create materials that can be easily customized without changing the shader code.

Here is an example of a shader with a color property:

Shader "Custom/ColorShader" {
    Properties {
        _Color ("Color", Color) = (1, 1, 1, 1)
    }
    SubShader {
        Pass {
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            
            float4 _Color;
            
            float4 vert(float4 pos : POSITION) : SV_POSITION {
                return UnityObjectToClipPos(pos);
            }
            
            float4 frag() : SV_Target {
                return _Color;
            }
            ENDCG
        }
    }
}

In this shader, a color property called _Color is defined. In the Unity Editor, you can now change the color of the material, and the shader will use the specified color when rendering.

Advanced Shader Techniques

Once you are comfortable with the basics, you can explore more advanced shader techniques. Some of these include:

• Normal Mapping: This technique simulates small surface details without adding extra geometry. It uses a normal map texture to alter the surface normals, creating the illusion of depth and detail.
• Specular Highlights: By calculating reflections and light interactions, specular highlights can add realism to shiny surfaces.
• Parallax Mapping: A more advanced technique than normal mapping, parallax mapping further enhances the illusion of depth by offsetting texture coordinates based on the viewer's perspective.
• Post-Processing Effects: These are shaders applied to the entire screen after rendering. They can create effects like bloom, motion blur, and color grading.

Cross-Platform Considerations

When developing shaders for multi-platform games, it's important to consider the performance and capabilities of different devices. Mobile devices, for example, have less powerful GPUs compared to PCs or consoles. Therefore, optimizing shaders for performance is crucial to ensure smooth gameplay across all platforms.

Some tips for optimizing shaders include:

• Minimize the number of texture lookups and mathematical operations in your shaders.
• Use simpler shaders or fallback shaders for less powerful devices.
• Profile your shaders using Unity's built-in tools to identify bottlenecks.

Unity's support for multiple rendering pipelines, such as the Built-in Render Pipeline, the Universal Render Pipeline (URP), and the High Definition Render Pipeline (HDRP), also affects shader development. Each pipeline has its own set of features and optimizations, so understanding the differences can help you make informed decisions when developing shaders for your game.

In conclusion, shader programming is a powerful tool in the game developer's arsenal. By mastering shaders, you can create visually stunning effects, optimize performance, and ensure your game looks great on any platform. As you continue to explore and experiment with shaders, you'll unlock new possibilities for creativity and innovation in your game development projects.