PBRTexture

PBRTexture

This demo shows how to render using Physically Based Rendering (PBR) techniques as outlined in https://learnopengl.com/PBR/Lighting

In particular this demo uses a class called texture_pack which can read in a json file containing a list of textures and locations for easy texture management.

uv run main.py

WebGPU version

PBRTextureWebGPU.py renders the same scene with wgpu-py instead of OpenGL, reusing the same textures/ and textures.json. Whilst I mainly use WebGPU for my teaching now I wanted a side-by-side with the OpenGL demo so the difference in how textures are handled is obvious.

uv run PBRTextureWebGPU.py

The interesting part is texture_pack_webgpu.py. OpenGL binds the five maps (albedo, normal, metallic, roughness, AO) to global texture units and re-binds all five before every draw with glActiveTexture. WebGPU has no global texture-unit state — resources reach the shader through bind groups — so each material loads its maps into their own GPUTexture and bakes a single GPUBindGroup up front. Selecting a material at draw time is then one set_bind_group call rather than five rebinds.

The rest follows the WebGPU idioms: an explicit three-group layout (per-object transforms in @group(0), lights and camera in @group(1), the material pack in @group(2)), and a dynamic-offset uniform buffer with one padded slot per teapot so the whole grid draws in a single render pass. The shader PBRTexture.wgsl is a straight port of the GLSL, with dpdx/dpdy standing in for dFdx/dFdy in the tangent-space normal mapping.

Controls are the same as the OpenGL demo: arrow keys move the camera, left mouse rotates, the wheel zooms, 1–4 toggle the lights, L toggles the light spheres, R reseeds the layout and Space resets the camera.

Future work

The WebGPU version keeps close to the OpenGL structure rather than chasing performance, so there is room to improve:

• The greyscale metallic/roughness/AO maps are uploaded as full RGBA, which wastes three quarters of the memory. Loading them as r8unorm and sampling .r would be leaner.
• Textures are uploaded with a single mip level, so distant teapots alias a little. The OpenGL demo generates mipmaps; WebGPU has no glGenerateMipmap, so this needs a small blit chain to fill the mip levels.
• Every teapot gets its own bind group and a per-frame uniform write. Instanced drawing, or a storage buffer of per-instance transforms indexed by instance_index, would cut the draw and upload cost.

References

• LearnOpenGL — PBR Theory and PBR Lighting — the textured metallic/roughness workflow implemented here.
• R. L. Cook & K. E. Torrance, "A Reflectance Model for Computer Graphics", ACM TOG 1982 — ACM — the microfacet BRDF underlying modern PBR.
• B. Karis, "Real Shading in Unreal Engine 4", SIGGRAPH 2013 course — course page — the GGX/Smith/Schlick term choices most real-time PBR follows.
• FreePBR — source of the albedo/normal/metallic/roughness/AO texture sets.