OpenGL Renderer

A real-time renderer written from scratch in C++17 and OpenGL 4.5,
used as a playground to implement and understand rendering techniques.

Features • Gallery • Getting started • Controls • Architecture • Documentation • Roadmap

Features

Shading

• Physically based materials (glTF metallic-roughness): albedo, metallic, roughness, normal, occlusion and emissive maps
• Cook-Torrance BRDF: GGX distribution, height-correlated Smith visibility, Schlick Fresnel
• OBJ and other Phong materials converted on import (Kd, Ks, Ns, Ke)
• HDR rendering, exposure and ACES filmic tone mapping, sRGB-correct pipeline

Lights and shadows

• A sun plus up to 64 point and 16 spot lights, all ECS entities with a finite range and windowed inverse-square falloff
• Cascaded shadow maps for the sun: 4 cascades in a single pass with geometry shader instancing, per-cascade culling, texel snapping against shimmering, normal offset and slope-scaled bias, 3x3 PCF
• Alpha-tested foliage and fences, in both the lighting and the shadows

Engine

• Per-frame data in std140 uniform blocks, shared between C++ and GLSL through a single interface header
• Direct state access and immutable storage for every OpenGL object
• Frustum culling, draw sorting by material
• Shader preprocessor with #include and injected constants
• Assimp import (OBJ, glTF, FBX...), shared caches for textures, shaders and models
• Entity-component scene on EnTT

Tooling

• Dear ImGui panel to edit lights, shadows, exposure and the camera live
• Debug views for each material channel and for the shadow cascades
• Sun drawn in the sky and light markers, to check lighting at a glance
• Command-line scene loading and screenshots, for scripted captures
• Debug groups around every pass for RenderDoc and Nsight

Gallery

Cascaded shadow maps	Cascade debug view
Crytek Sponza (converted OBJ materials)	Damaged Helmet (glTF PBR)

_{Albedo, normals, roughness and metallic debug views of the Damaged Helmet}

Getting started

Requirements

• A C++17 compiler (GCC, Clang or MSVC) and CMake 3.10+
• A GPU and driver supporting OpenGL 4.5. Developed on Linux with Mesa. Windows should work but is untested. macOS stops at OpenGL 4.1 and is not supported.

Every library is vendored in vendor/, nothing else to install.

Build and run

git clone https://github.com/Mounarkk/OpenGL-renderer.git
cd OpenGL-renderer
cmake -B build -DCMAKE_BUILD_TYPE=Release
cmake --build build -j
./build/opengl_renderer

The project directory is baked into the executable, so it finds config.txt and res/ from any working directory.

Assets

Models are not versioned, download them into res/models/:

Scene	Source	Folder
Default scene (backpack)	LearnOpenGL	res/models/backpack/
Sponza, Cornell Box, San Miguel...	McGuire Computer Graphics Archive	any
glTF PBR test models	Khronos glTF Sample Assets	the glTF folder of a model

Embedded textures (.glb) are not supported yet.

Controls

Input	Action
WASD Space Ctrl	Move, hold Shift to go faster
Mouse, scroll	Look around, zoom
← → / ↑ ↓	Turn / raise the sun
L	Toggle the point and spot lights
C	Toggle the cascade debug view
Tab	Switch the mouse between the camera and the panel
F1	Hide the panel
F12	Save a screenshot to screenshots/

Option	Effect
--model <file>	Open a model instead of the default scene
--scale <factor>	Uniform scale of the model
--flip-uvs	For files authored with a top-left UV origin
--camera x,y,z,yaw,pitch	Initial camera, angles in degrees
--sun azimuth,elevation	Initial sun direction, in degrees
--sun-only	Start without the point and spot lights
--cascades	Start with the cascade debug view
--debug-view <channel>	albedo, normals, metallic, roughness, occlusion or emissive
--screenshot <file>	Render a few frames, save a PNG and quit

# The Sponza shot of the gallery
./build/opengl_renderer --model "res/models/sponza/sponza.obj" --scale 0.01 \
    --camera -11,1.5,-0.5,0,5 --screenshot sponza.png

Architecture

A frame of the forward renderer:

flowchart LR
    Scene[(EnTT scene)] -->|meshes, lights| Submit[Submit<br/>culling, sorting]
    Submit --> UBO[Frame and light<br/>uniform blocks]
    UBO --> Shadow[Shadow pass<br/>4 cascades, 1 draw per mesh]
    Shadow -->|depth array| Lighting[Lighting pass<br/>GGX, HDR target]
    Lighting --> Sky[Skybox and<br/>light markers]
    Sky --> Post[Post-process<br/>exposure, ACES, gamma]
    Post --> UI[ImGui panel]

Loading

src/
├── application/   window, main loop, test scenes, command line
├── core/          configuration, logging, exceptions
├── gl/            RAII wrappers over OpenGL objects (DSA)
├── rendering/     renderer, passes, materials, frustum, shader interface
├── resource/      Assimp import, texture, shader and model caches
├── scene/         EnTT scene, components, camera
└── ui/            Dear ImGui debug panel
res/shaders/       GLSL, common/ holds the shared uniform blocks and BRDF
docs/              notes on the techniques

Documentation

Notes written while implementing each technique, with the reasoning behind the choices:

• Cascaded shadow maps: splits, stable fitting, single-pass rendering, biasing
• Physically based shading: material model, BRDF, conversion of older formats, tone mapping
• Shader interface: uniforms, uniform blocks, binding points, std140

Roadmap

• Cascaded shadow maps
• OpenGL 4.5, uniform buffers, ECS lights, frustum culling
• Physically based materials and tone mapping
• Image based lighting
• Spot light shadows, point light shadow atlas
• Clustered light culling in compute
• Volumetric fog

Details in TODO.md.

Acknowledgements

Libraries: GLFW, glad, GLM, Assimp, EnTT, spdlog, stb and Dear ImGui.

Damaged Helmet by theblueturtle_ (CC BY-NC 4.0), glTF conversion by ctxwing (CC BY 4.0).