Impromptu

This is my personal CPU-based 3D raster graphics engine that implements a minimal 3D graphics API. The intent of this project is to give me a better understanding of what implementations of graphics APIs such as OpenGL, Vulkan, and Direct3D do under the hood.

The only required external library is SDL2 (for window and user input management).

By default, Impromptu uses perspective projection with first-person camera controls.

Building and Running

I build the project with gcc on Windows. The build command I use in development looks something like

gcc -pedantic -Wall -Werror -fgnu89-inline -std=c99 ^
main.c engine.c model.c vector3.c matrix4.c^
-I[Path to SDL2 includes] ^
-L[Path to SDL2 libraries] ^
-lSDL2 -lSDL2main -lmingw32 ^
-O2 ^
-o impromptu.exe 

When running the program, make sure SDL2.dll (can be found in the SDL2 link above) is in the same directory as the output executable.

Resources

In no particular order, here are some online resources I found helpful along the way:

URL	Description
https://www.songho.ca/opengl	Detailed (occasionally math-heavy) explanations of OpenGL concepts.
https://learnopengl.com	General overview of OpenGL concepts.
https://www.pbr-book.org/4ed	Although this book is on physically based rendering of images via raytracing, it is very rigorous in it's explanations of coordinate spaces and transformations for 3D rendering in general.
https://computergraphics.stackexchange.com	A forum with expert answers for all things computer graphics.
https://github.com/SeanJxie/3d-engine-from-scratch/tree/main	An old project of mine. I had next to no linear algebra experience. Everything's a mess. Impromptu is a reattempt of what I had desired to build back then.
https://www.youtube.com/watch?v=ih20l3pJoeU	Tutorial I followed for the project above
https://stackoverflow.com/questions/4124041/is-opengl-coordinate-system-left-handed-or-right-handed	SO question about OpenGL's coordinate handedness. Impromptu uses only left-handed coordinate systems.
https://en.wikipedia.org/wiki/Z-buffering	The Z-culling section explains how the reverse "painter's algorithm" can be used to optimize Z-culling.
https://www.khronos.org/opengl/wiki/Depth_Buffer_Precision and https://developer.nvidia.com/content/depth-precision-visualized	OpenGL wiki and Nvidia article on depth buffer imprecision (and suggestions to improve precision).
https://bruop.github.io/frustum_culling/	Article on frustrum culling.
https://gabrielgambetta.com/computer-graphics-from-scratch/11-clipping.html	Article on triangle clipping.
https://learnwebgl.brown37.net/08_projections/projections_perspective.html	Nice interactive demonstration and derivation of the perspective projection matrix.
http://www.opengl-tutorial.org/beginners-tutorials/tutorial-6-keyboard-and-mouse/	First-person controls.
https://www.pbr-book.org/4ed/Geometry_and_Transformations/Applying_Transformations#Normals and https://www.scratchapixel.com/lessons/mathematics-physics-for-computer-graphics/geometry/transforming-normals.html and https://stackoverflow.com/questions/13654401/why-transform-normals-with-the-transpose-of-the-inverse-of-the-modelview-matrix	Text on why normals can not be treated as direction vectors when applying transformations.
https://www.khronos.org/opengl/wiki/Rendering_Pipeline_Overview	OpenGL wiki on the rendering pipeline. Impromptu aims to perform small vital stages of the pipeline.
https://en.wikipedia.org/wiki/Back-face_culling	Rundown on back-face culling
https://paulbourke.net/dataformats/obj/ and https://paulbourke.net/dataformats/mtl/	OBJ and MTL file specs
https://www.scratchapixel.com/lessons/3d-basic-rendering/rasterization-practical-implementation/rasterization-stage.html	A triangle rastization algorithm with a solid explanation of barycentric coordinates.
https://docs.safe.com/fme/html/FME-Form-Documentation/FME-ReadersWriters/!FME_Geometry/Texture_Coordinates.htm	Rundown on texture coordinates with some nice references.
https://computergraphics.stackexchange.com/questions/8515/how-is-lighting-done-in-rasterization-based-pipeline	Into question on lighting in in the context of rasterization.
https://en.wikipedia.org/wiki/Computer_graphics_lighting#:~:text=In%20computer%20graphics%2C%20the%20overall,diffuse%2C%20ambient%2C%20and%20specular.	General graphics lighting terminology
https://learnwebgl.brown37.net/09_lights/lights_diffuse.html#diffuse-lighting	This and following chapters provide vertex and fragement shaders implementing diffuse/specular/ambient lighting