Graphics Engine

Contributors: Gephel Kogyal and Alex Shao

A software 3D rendering engine written in C, driven by MDL (My/Modeling/Description Language), a small domain-specific scripting language parsed with flex/bison. It rasterizes polygon meshes and parametric solids into PPM/PNG images, supports flat, Gouraud, and Phong shading, perspective projection, animation, and can load external .obj/.stl meshes.

Created alongside JonAlf Dyrland-Weaver's computer graphics course. Files were archived, but commit history lost to school organization's data purge.

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Features

• MDL scripting language: a text-based scene description format (parsed via mdl.l / mdl.y) for defining shapes, transformations, coordinate systems, lighting, and animation.
• Primitives: spheres, tori, boxes, lines, circles, Bezier and Hermite curves.
• Mesh import: load external triangle meshes from .obj and .stl files (mesh_parser.c).
• Transformation stack: push/pop coordinate system stack with translate, scale, and rotate operations, plus named/saved coordinate systems.
• Shading modes: flat, Gouraud, and Phong shading with ambient, diffuse, and specular lighting (gmath.c, draw.c).
• Perspective projection: simple pinhole-camera perspective division as well as an OpenGL-style perspective matrix (perspective.c).
• Z-buffering: hidden-surface removal via a per-pixel z-buffer.
• Animation: frames/vary/tween knobs interpolate values across frames, rendering an image sequence that's stitched into a GIF via ImageMagick's convert.
• Output: save frames as PPM or PNG (stb_image_write), or pop up a live SDL2 window with display.

Dependencies

• gcc
• flex
• bison
• SDL2 and SDL2_image (for live display via sdl2-config)
• ImageMagick's convert command (for animation/GIF assembly)

On Debian/Ubuntu: sudo apt install flex bison libsdl2-dev libsdl2-image-dev imagemagick

Building

make

This runs flex on mdl.l and bison on mdl.y to generate the lexer/parser (lex.yy.c, y.tab.c, y.tab.h), compiles all engine sources, and links everything into an mdl executable.

make clean

Removes generated parser files, object files, and rendered output (*.o, *.png, *.gif, contents of anim/ and images/).

Usage

./mdl script.mdl

or, to build and immediately run the sample script bundled in the makefile:

make run

which builds the parser and runs ./mdl thingmabob.mdl.

If no script is provided, the parser reads from stdin.

Project Structure

File	Purpose
mdl.l	Flex lexer for the MDL language
mdl.y	Bison grammar; builds the opcode list (op[]) consumed by the interpreter and drives main()
my_main.c	Interprets the parsed MDL opcode list frame-by-frame: manages the coordinate stack, lighting, shading mode, perspective, and drawing
parser.h (referenced)	Shared opcode/command struct definitions
symtab.c	Symbol table for named constants, lights, coordinate systems, and knob values
stack.c	Coordinate-system transformation stack
matrix.c	4xN matrix type: identity, translate/scale/rotate matrices, multiplication, Bezier/Hermite coefficient generation
draw.c	Shape generation (spheres, tori, boxes, circles, curves) and scanline rasterization (flat, Gouraud, Phong) plus Bresenham line drawing
gmath.c	Lighting math: ambient/diffuse/specular calculation, vertex normal averaging for smooth shading
perspective.c	Perspective projection (pinhole model and OpenGL-style projection matrix)
mesh_parser.c	.obj and .stl mesh file loading
display.c	Screen/z-buffer manipulation, PPM/PNG output, ImageMagick animation assembly, SDL2 live display
print_pcode.c	Debug utility to print the parsed opcode list
main.c	Legacy/alternate entry point exercising the engine directly in C (not used by the mdl build target)
makefile	Build rules

Rendering pipeline

1. mdl.y/mdl.l parse the script into an array of opcodes (op[]).
2. my_main.c runs a first pass to determine frame count and basename, then a second pass to compute per-frame knob values for animated scenes.
3. For each frame, opcodes are replayed in order: shapes are generated into a temporary point matrix, transformed by the current coordinate system, optionally perspective-projected, and rasterized into the screen buffer with z-buffering.
4. Completed frames are saved as PNG (single image) or as a numbered sequence in anim/ (animation), which is then assembled into a GIF with ImageMagick.