GTA: One draw call

GTA: One dra... what?

The main goal of this project is to render the cities from GTA games in only 1 draw call. Such renderer must be interactive and render the whole city each frame.

But why?

Initially this project served as testbed for learning AZDO OpenGL techniques. Since some people are still struggling to render ~100 meshes at 30 FPS, and because I haven't seen a project like this, I decided to challenge myself... You can also use this renderer to find some easter eggs - I did :)

How on earth?

Simply put: clever data reordering and OpenGL 4.3 Core with bindless textures! The biggest problem was to figure out how to access all the textures at once. Since I'm still using a previous-gen GPU that does not support bindless textures nor gl_DrawID I tried evaluating various texture preprocessing tricks until I stumbled upon the maximum number of textures inside GL_TEXTURE_2D_ARRAY... so I ended up using GL_ARB_bindless_texture and GL_ARB_shader_draw_parameters extensions and testing it at my friend's workstation.

The overall algorithm is pretty simple:

1. Group all textures with the same format together (offline)
2. Upload all texture groups to GPU using glTexImage3D() and glCompressedTexImage3D()
3. glGetTextureHandleARB() and make them resident with glMakeTextureHandleResidentARB()
4. Fill buffers with baked data (mesh vertices and indices, instance matrices, indirect buffer)
5. Load, compile and link vertex and fragment shaders
6. Do the magic with a single call to glMultiDrawElementsIndirect()

You convinced me. How to use it?

Requirements

If your checklist looks like this below, you are ready to build the project from source code!

• A legal copy of GTA Vice City (this application requires the original asset files)
• GPU that supports at least OpenGL 3.3 Core Profile
• SDL2 library downloaded
• GLEW 1.13 library downloaded
• premake5 installed for different configuration

You can also download the binaries, but you still have to fulfill the first 2 requirements above.

Building from source and running

1. Make sure that SDL2_ROOT and GLEW_ROOT environment variables are set (at least on Windows)
2. premake5 gmake or premake5 vs2013 (depending on your OS / VS version) if you want to build with different configuration (I've included VS2015 solution with minimal feature set for you)
3. Go to build directory and build the generated project (using make or Visual Studio)
4. Copy the compiled vicebaker application to the game installation directory, create an empty _extracted directory there and run vicebaker in order to preprocess the assets (no harm will be done to original files). The baking should take less than a minute and requires about 300 MB free space on your HDD. After baking, you can safely remove this "_extracted" directory.
5. Copy the generated *.blob files back to the directory with vicerender and launch it!

Action	Reaction
Left Mouse Button	Look around
W/S/A/D	Standard FPP movement
Q/E	Fly up/down
Left Shift	Increase movement speed

The end?

Of course not! There are still some things that might be worth considering:

• Import and render Vice City
• Achieve 1 draw call
• Provide fallback for unsupported GPUs (more than 1 draw-call)
• Optional asset compression (LZHAM)
• Some textures seem to be wrong (those hash collisions...)
• Fix issues with some triangle-stripped meshes (mostly in Mainland)
• Sort transparent objects back-to-front
• Loosen some constrains to implement view-frustum culling
• Add Liberty City from GTA III
• Improve the visual quality somehow (via Über-shader?)
• Reversed floating-point depth buffer (no more Z-fighting)
• Support for hour-constrained models and night time
• Improve Code quality & readability
• Experimental PlayStation 3 port

Unfortunately due to the 1 draw-call constraint there will be no run-time shadows or any post-processing effects :/ Yeah, I know - what a pitty... ;)