Master of Puppets

Location

src/rasterizer/
  rasterizer.h    — Public interface (types + functions)
  rasterizer.c    — Implementation

Overview

The software rasterizer is shared rendering infrastructure. It provides framebuffer management, frustum clipping, triangle rasterization, and line drawing. Any backend that needs CPU-side rasterization can include "rasterizer/rasterizer.h" and call these functions directly.

The CPU backend (src/backend/cpu/) delegates all rendering to this module.

Types

MopSwFramebuffer

typedef struct MopSwFramebuffer {
    int       width, height;
    uint8_t  *color;       /* RGBA8, size = width * height * 4 */
    float    *depth;       /* float,  size = width * height     */
    uint32_t *object_id;   /* uint32, size = width * height     */
} MopSwFramebuffer;

All buffers use top-left origin. Row stride equals width.

MopSwClipVertex

typedef struct MopSwClipVertex {
    MopVec4  position;   /* clip-space (before perspective divide) */
    MopVec3  normal;     /* world-space normal */
    MopColor color;      /* vertex color */
} MopSwClipVertex;

Functions

Framebuffer Management

Function	Description
`mop_sw_framebuffer_alloc`	Allocate color, depth, and ID buffers
`mop_sw_framebuffer_free`	Free all framebuffer storage
`mop_sw_framebuffer_clear`	Clear to color, depth 1.0, object_id 0

Rasterization

Function	Description
`mop_sw_rasterize_triangle`	Clip, shade, and rasterize a triangle
`mop_sw_clip_polygon`	Sutherland-Hodgman frustum clipping
`mop_sw_draw_line`	Bresenham line drawing with depth

Clipping

mop_sw_clip_polygon clips against 6 frustum planes in clip space using the Sutherland-Hodgman algorithm:

+X: w + x ≥ 0    -X: w - x ≥ 0
+Y: w + y ≥ 0    -Y: w - y ≥ 0
+Z: w + z ≥ 0    -Z: w - z ≥ 0

Maximum output vertices per triangle: 24. Vertex attributes (position, normal, color) are linearly interpolated at clip boundaries.

Rasterization

mop_sw_rasterize_triangle is the main entry point. It performs:

Frustum clipping via mop_sw_clip_polygon
Triangle fan decomposition of the clipped polygon
For each sub-triangle:
- Perspective divide (xyz / w) → NDC
- Viewport transform → screen pixels (Y flipped for top-left origin)
- Backface culling (screen-space signed area)
- Flat shading: ambient 0.2 + diffuse 0.8 × max(N·L, 0)
- Half-space edge function rasterization (solid) or Bresenham (wireframe)
- Per-pixel depth test → write color, depth, object_id

Line Drawing

mop_sw_draw_line implements Bresenham's algorithm with depth interpolation. Used for wireframe mode.