DirectX Computational Graphics

The Graphics Pipeline

The graphics pipeline is a series of processing stages that transform 3D scene data into a 2D image displayed on the screen. DirectX implements this pipeline in hardware (GPU) for high-performance rendering.

• Input Assembler: Takes vertex data from memory and organizes it into primitives (points, lines, triangles).
• Vertex Shader: Processes each vertex individually, transforming its position and other attributes (e.g., color, texture coordinates) from object space to screen space.
• Tessellation Shaders (Optional): Dynamically adds geometric detail to models, allowing for more complex shapes without increasing base mesh complexity.
• Geometry Shader (Optional): Can generate or discard entire primitives, offering advanced control over geometry.
• Rasterizer: Converts geometric primitives into pixels (fragments) that will be drawn on the screen.
• Pixel Shader: Determines the final color of each pixel, often involving texturing, lighting calculations, and material properties.
• Output Merger: Combines the results from the pixel shader with the existing frame buffer, handling depth testing, blending, and stencil operations.

This pipeline is highly programmable, allowing developers to customize its behavior using shaders.

Shaders

Shaders are small programs that run on the GPU. They are the heart of modern graphics programming, enabling custom effects and complex computations.

• Shader Model: Defines the capabilities and features available to shaders. DirectX supports various shader models, with newer models offering more advanced functionality.
• High-Level Shading Language (HLSL): The primary language used to write shaders for DirectX. It's a C-like language that compiles down to GPU-specific bytecode.

Common shader types include Vertex, Pixel, Geometry, Hull, Domain, and Compute shaders.

// Example HLSL vertex shader
struct VertexShaderInput {
    float4 position : POSITION;
    float4 color : COLOR;
};

struct VertexShaderOutput {
    float4 position : SV_POSITION;
    float4 color : COLOR;
};

VertexShaderOutput main(VertexShaderInput input) {
    VertexShaderOutput output;
    output.position = input.position; // In clip space for simplicity
    output.color = input.color;
    return output;
}

Data Structures and Memory

Efficient data management is key for performance.

• Vertex Buffers: Store vertex data (position, normals, texture coordinates, etc.).
• Index Buffers: Store indices that reference vertices in vertex buffers, allowing for efficient reuse of vertices and creation of complex geometry.
• Constant Buffers: Store data that is constant across multiple vertices or pixels (e.g., transformation matrices, light properties).
• Texture Buffers: Store image data used for texturing surfaces.

Coordinate Spaces

Understanding transformations between different coordinate spaces is fundamental to positioning and orienting objects in a scene.

• Object Space: The local coordinate system of an individual model.
• World Space: A common coordinate system where all objects in the scene are placed.
• View Space (Camera Space): Transforms objects relative to the camera's position and orientation.
• Clip Space: The final stage before projection, where clipping occurs to remove geometry outside the view frustum.
• Screen Space (Viewport Space): The 2D coordinate system of the display screen.

These transformations are typically handled by matrices (Model, View, Projection matrices).

Rendering Techniques

Various techniques are employed to achieve realistic visual effects.

• Lighting Models: Simulate how light interacts with surfaces (e.g., Phong, Blinn-Phong, physically based rendering (PBR)).
• Texturing: Applying images (textures) to surfaces to add detail and color.
• Materials: Define the surface properties of an object, including color, reflectivity, and roughness.
• Anti-aliasing: Techniques to reduce "jaggies" or stair-step artifacts on edges.

Compute Shaders

Beyond graphics rendering, DirectX provides Compute Shaders for general-purpose parallel computation on the GPU. This opens up possibilities for tasks like:

• Physics simulations
• Image processing
• Data analysis
• AI computations