DirectX Computational Graphics: Shading Techniques

Shading Techniques

Shading is the process of determining the color of each pixel on a rendered surface. In DirectX, this is primarily achieved through programmable shaders, which provide immense flexibility in creating complex visual effects. This section explores fundamental and advanced shading techniques that bring your 3D worlds to life.

Types of Shaders

DirectX utilizes several types of shaders, each with a specific role in the rendering pipeline:

Vertex Shader: Processes individual vertices, transforming them from model space to clip space and calculating per-vertex attributes like normals and texture coordinates.
Pixel Shader (or Fragment Shader): Processes individual pixels (or fragments) after rasterization. It determines the final color of each pixel based on interpolated vertex data, textures, lighting, and complex calculations.
Geometry Shader: An optional shader stage that can generate or discard primitives (points, lines, triangles) based on input primitives. Useful for effects like fur or grass generation.
Hull Shader & Domain Shader: Used for tessellation, allowing for the dynamic subdivision of geometry to add fine details.
Compute Shader: A general-purpose shader stage that can be used for non-graphics computations, such as physics simulations, particle systems, or advanced image processing.

Basic Shading Models

Before diving into programmable shaders, understanding traditional shading models is crucial:

1. Flat Shading

Assigns a single color to an entire polygon, typically calculated at one vertex and interpolated across the face. This results in a faceted appearance.

2. Gouraud Shading

Performs lighting calculations at each vertex and then interpolates the resulting colors across the polygon. This provides smoother shading than flat shading but can still exhibit visual artifacts, especially with dynamic lighting.

3. Phong Shading

Interpolates vertex normals across the polygon and performs lighting calculations per pixel. This yields significantly smoother and more realistic highlights and shading.

Programmable Shaders in DirectX

DirectX's power lies in its programmable shaders, written in High-Level Shading Language (HLSL).

Vertex Shader Example (Conceptual HLSL)

A simple vertex shader might transform vertex positions and pass through texture coordinates:

                
struct VS_INPUT {
    float4 Pos : POSITION;
    float2 Tex : TEXCOORD0;
};

struct VS_OUTPUT {
    float4 Pos : SV_POSITION;
    float2 Tex : TEXCOORD0;
};

VS_OUTPUT main(VS_INPUT input) {
    VS_OUTPUT output = (VS_OUTPUT)0;
    output.Pos = mul(input.Pos, g_worldViewProjection); // Apply transformations
    output.Tex = input.Tex;
    return output;
}
                
            

Pixel Shader Example (Conceptual HLSL)

A basic pixel shader might sample a texture and apply a simple ambient color:

                
Texture2D g_texture : register(t0);
SamplerState g_sampler : register(s0);

float4 main(float2 texCoord : TEXCOORD0) : SV_TARGET {
    float4 texColor = g_texture.Sample(g_sampler, texCoord);
    return texColor * float4(0.2f, 0.2f, 0.2f, 1.0f); // Ambient color
}
                
            

Advanced Shading Techniques

Physically Based Rendering (PBR): Simulates the physical properties of light and materials for highly realistic results. This includes concepts like albedo, metallic, roughness, and specular maps.
Normal Mapping: Uses a texture (normal map) to simulate surface detail by perturbing the surface normal per pixel, creating the illusion of intricate geometry without increasing polygon count.
Parallax Mapping / Height Mapping: Extends normal mapping by using a height map to simulate depth and self-shadowing, further enhancing the illusion of geometric detail.
Shader-Based Lighting Models: Implementation of complex lighting equations like Blinn-Phong, Cook-Torrance, or even custom lighting for unique artistic styles.
Subsurface Scattering (SSS): Simulates light that penetrates the surface of an object, scatters within it, and exits at a different point, crucial for materials like skin or wax.
Global Illumination: Techniques that simulate indirect lighting (light bouncing off surfaces), creating more realistic and immersive scenes.