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A software rasterizer.

This is my first stab at writing a library for software rasterization. It is far from ready in its current form, but it works and can be modified as needed. The rasterization routing expects a 2D array of pixels to be rendered onto, and a list of triangles to be rasterized.

Currently everything lives in main.c and types.h. Eventually I would like to build this into a single-header static library like those maintained by Sean Barrett.

Dependencies

  • gcc
  • kdbg
  • sdl2

Setup

cd /path/to/project
source env/shell

Building

build

Running

run triangles.def

Debugging

debug triangles.def &

Developer Information

Rasterization Outline

Given a polygon in viewspace ((0,0), (640,480)) we want to rasterize the polygon onto our viewspace buffer. At this point we can skip our modelview and projection matrices. We need a polygon rasterization algorithm, whether that directly involves line drawing or not. See here: http://www.sccs.swarthmore.edu/users/05/zap/labs/E26/lab7/index.html (We will also probably need a z-buffer once we start dealing with more than one object.)

Rasteriazation Algorithm

  • Convert each polygon into a list of edges. (Line segments.)
  • Sort all polygons front to back (ignore transparency support for now).
  • For each scanline keep track of which polygon has been intersected via the scanline stack.
  • This requires a line-line intersection algorithm in view space.
  • For now just use a solid, unique color for each individual polygon.

We'll have a list of polygons and divide the video buffer into lines. For each line that we'll rasterize, we want to subdivide it into line segments corresponding with polygons. So we'll need a stack representing the current polygon we're on. For every polygon we encounter in the stack while rasterizing, we need to do a per-pixel material calculation for that polygon. Ie., lighting + shading + textures + bump/parallalax.

Rasterization Limitations

At this point (2016-06-21) this program only handles scanline rasterization. The assumption is that we have a collection of adjacent, non-overlapping triangles in screen space. These triangles are the end result of the 3D rendering engine and no longer need Z-depth.

To Do

  • Define materials beyond simple colors.
  • Interpolate materials across triangle surfaces.

NOTE: I'm not actually entirely clear on how real rasterizers integrate with rendering engines and what information they have for rasterization. I am assuredly conflating 3D transformations, rendering and rasterization to various extents and should do some more study to sort that out.

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