C3D

C3D is a small graphics API for 2D/3D-style rendering backed by NVIDIA CUDA. It was built for fun and experimentation, not as a serious production renderer or a replacement for a native graphics API.

It exposes a compact graphics-like interface for:

• stage buffers
• textures
• vertex and index buffers
• command buffers
• render passes
• line, quad, and triangle draws
• swapchain

The repo also includes a Windows demo in test/main.cpp that renders into a CUDA texture, copies the result back to the CPU, and presents it with GDI.

Several write and render-path calls also support internal object cycling through the cycle flags. The behavior is intended to work like SDL_gpu: the API can rotate to a fresh internal backing resource to avoid stomping data that may still be in flight on the GPU.

Why I Built This

I built C3D to experiment with a graphics API shape without depending on a full native graphics stack like Direct3D, Vulkan, or OpenGL.

The idea is to keep the public API small and C-friendly, but run the heavy lifting on CUDA.

This project is intentionally lightweight and exploratory. The goal is to learn, prototype, and test ideas, not to chase production readiness.

Project Layout

• inc/C3D.h: public API
• src/*.cu: CUDA implementation
• test/main.cpp: Windows demo application
• project.bbs: build description for the bbs build system

API Overview

The public header is organized around a few resource types plus a minimal command submission model:

graph TD
    Stage["Stage Buffers"] <--> Textures["Textures"]
    Textures <--> Swap["Swapchain"]
    Buffers["GPU Buffers"] <--> Cmd["Command Buffers"]
    Cmd <--> Textures
    Stage <--> Buffers
    Pass["RenderPass"] --> Cmd

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Building

To build the project, install bbs.

Then run bbs build from the repository root.

To build C3D with Tracy integrated through bbs, use one of the profiling configs:

bbs build -t c3d_test -c debug-profile

or

bbs build -t c3d_test -c release-profile

The debug and release configs build the normal targets without Tracy enabled. The debug-profile and release-profile configs enable TRACY_ENABLE for both the CUDA library and the demo while using the same c3d_lib / c3d_test targets.

Current Bottleneck

Right now the main bottleneck is Windows presentation through GDI.

C3D renders into CUDA-managed GPU memory, but the demo cannot present that memory directly to a window surface. Instead, it has to copy the rendered image back to CPU-visible memory and hand it off to GDI for presentation. That extra GPU-to-CPU transfer plus the GDI blit is currently the slowest part of the frame path.

Here is a Tracy capture from the demo showing the presentation path under inspection: