The Rendering Pipeline

Input Assembler

This stage reads the vertex data from buffers (e.g., vertex buffers, index buffers) and constructs primitives (points, lines, triangles) that are passed to the next stage.

• Vertex Data: Positions, normals, texture coordinates, colors, etc.
• Primitive Types: D3D_PRIMITIVE_TOPOLOGY enum defines how vertices form primitives.

Vertex Shader

The vertex shader operates on each vertex individually. Its primary role is to transform vertices from model space into clip space using matrices (world, view, projection).

• Input: Per-vertex data.
• Output: Transformed vertex position in clip space, and other vertex attributes (e.g., color, texture coordinates) passed to subsequent stages.
• Common Operations: Matrix transformations, vertex lighting.

struct VS_INPUT {
    float4 Pos : POSITION;
    float4 Color : COLOR;
};

struct VS_OUTPUT {
    float4 Pos : SV_POSITION;
    float4 Color : COLOR;
};

VS_OUTPUT VS(VS_INPUT input) {
    VS_OUTPUT output = (VS_OUTPUT)0;
    output.Pos = mul(input.Pos, g_WorldViewProjection); // g_WorldViewProjection is a matrix
    output.Color = input.Color;
    return output;
}
                

Tessellation (Optional)

This optional stage adds detail to geometry by subdividing primitives into smaller ones dynamically. It consists of three programmable stages:

• Hull Shader: Controls tessellation factors and outputs control points.
• Tessellator: Generates new vertices based on tessellation factors.
• Domain Shader: Calculates the final positions and attributes of the newly generated vertices.

Geometry Shader (Optional)

The geometry shader can operate on entire primitives (points, lines, triangles) and can generate new primitives or discard existing ones. It's often used for effects like particle systems or fur rendering.

• Input: Primitives.
• Output: Primitives (can be a different type or count).

Rasterizer

The rasterizer converts geometric primitives into a set of pixels (fragments) that cover the screen area. It performs clipping, perspective division, and viewport transformation.

• Clipping: Removes geometry outside the view frustum.
• Viewport Transform: Maps clip-space coordinates to screen-space coordinates.
• Scan Conversion: Determines which pixels are covered by each primitive.

Pixel Shader (Fragment Shader)

The pixel shader operates on each fragment generated by the rasterizer. It determines the final color of each pixel by performing operations like texturing, lighting calculations, and applying material properties.

• Input: Interpolated per-vertex attributes (color, texture coordinates, etc.) and textures.
• Output: Final color for a pixel (SV_TARGET).
• Common Operations: Texture sampling, complex lighting models, post-processing effects.

struct PS_INPUT {
    float4 Pos : SV_POSITION;
    float4 Color : COLOR;
};

float4 PS(PS_INPUT input) : SV_TARGET {
    // Simple color output
    return input.Color;
}
                

Output Merger

The output merger stage combines the output of the pixel shader with the contents of the render targets (frame buffer, depth buffer, stencil buffer). It handles depth testing, stencil testing, and blending.

• Depth Test: Determines if a pixel is visible based on its depth.
• Stencil Test: Uses stencil buffer values for advanced rendering effects.
• Blending: Combines the new pixel color with the existing color, typically for transparency.