the large pixel collider

The large pixel collider is a proof-of-concept graphics engine, implemented in C. The following sample animations display some of its functionality:

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compilation/installation

• make all, or ./large_pixel_collider : compile the engine.
• make test, or ./large_pixel_collider --test : run unit tests
• make run : render a sample animation.
• make run SCRIPT_FILE=path/to/script, or ./large_pixel_collider --script /path/to/script : execute the contents of a script file.
• make clean : delete compiled binaries
• make install : install all of the engine's dependencies, which are:
  • SDL
  • ncurses
  • Xlib
  • flex
  • bison

features

This project implements a rudimentary graphics engine from the ground up, using the SDL graphics library only for per-pixel access. The following algorithms and features are included:

• Bresenham line rasterization
• translations, scaling, rotations
• Bezier/Hermite curves
• shape creation: spheres, tori, rectangular prisms
• backface culling
• scanline fills
• z-buffering
• a custom scripting language, MDL, with a flex/bison parser and interpreter
• Goraud shading
• a unit-testing suite

use

basics

From the project root, run make install, and make all. When the engine finishes compilation, run make test to execute the engine's full suite of unit-tests: make sure they all succeeded! Then, run make run to see a sample animation.

more

Beyond the compiled animation displayed by make run, check out the following:

• animations: the engine comes pre-packaged with animation gifs inside animations/, which display some of its functionality.
• scripting: the engine has its own scripting language, MDL, which allows you to toy with its numerous features. Read on for more details.

scripting

The engine's scripts are written in a language called MDL, which consists of commands written on individual lines. A simple script might look like:

// A sample script that creates a sphere, then rotates, scales, and translates it.

frames 40
rotate x 45
move 10 30 40
scale 2 2 2
sphere 0 0 0 50
display

commands

Note on notation: all command prototypes will take the following form: command [args]. [args] will be a space and/or pipe separated list.

• a b means there are two arguments, a and b
• a|b indicates that only one argument, either a or b, is necessary
• [a] indicates that a is optional.

general commands

command	description
display	displays the image generated by the script thus far.
save filename	saves the image to a bmp file named filename.
frames number	execute the script over number frames.
vary modifier frame_begin frame_end val_begin val_end	Varies modifier from value val_begin to val_end over the span of frames frame_begin to frame_end.
//	a comment

transformations

Transformations are a bit tricky. The engine maintains a stack of transformation matrices: move, rotate, and scale all create transformations which are multiplied into the current top of the transformation matrix. pop will remove the top matrix, and push will duplicate it (creating a copy and pushing it onto the stack). Whenever a shape is created, it is transformed against the current top of the transformation matrix. Clever use of push and pop lets you "cascade" transformations: an arm with an attached hand can be angled outward, the hand can be rotated, and each of the fingers can then be angled down, while still maintaining the logical structure of the arm. Without the stack mechanism, all of the components would undergo the same transformations and the resultant object wouldn't resemble an arm at all (its parts probably scattered across the screen)!

The optional argument modifier appended to the following prototypes is any variable previously declared with the vary command.

command	description
pop	pops the top matrix off the transformation stack.
push	pushes a copy of the top matrix of the transformation stack onto the stack.
move x y z [modifier]	adds a translation of (x, y, z) units.
rotate x|y|z degrees [modifier]	adds a rotation of degrees degrees through the x, y, or z axes.
scale x y z [modifier]	adds a scale of (x, y, z) units.

object creation

command	description
box x y z h w d	adds a rectangular prism with top-left-front corner at (x, y, z), and height h, width w, and depth d.
torus x y z r0 r1	adds a torus with centroid (x, y, z), minor radius r0 and major radius r1.
sphere x y z r	adds a sphere centered on (x, y, z)

mechanics

An MDL script is executed over a given number of frames, which must be specified at the beginning of the script with the frame command. vary commands are used to change the value of modifiers, which can be used to amplify transformations, from one value to another over a given range of frames.

After the frame and vary commands are interpreted, the remainder of the script is executed once per frame, with different modifier values that change the resultant image.

Example

// display a torus spinning 360 degrees through the z-axis.
frames 360
vary angle 0 359 0 1

rotate z 360 angle
torus 0 0 0 50 100
display