Browser Shim

The shim provides just enough browser surface area for Three.js to run. It is not a general-purpose DOM implementation. The guiding rule is: implement what Three.js touches, no more.

API Surface (Initial)

• WebGLRenderingContext and WebGL2RenderingContext (subset)
• HTMLCanvasElement with getContext, width, height
• requestAnimationFrame and cancelAnimationFrame
• performance.now()
• Image, createImageBitmap
• fetch, FileReader, URL.createObjectURL, URL.revokeObjectURL
• Input via addEventListener (mouse, keyboard, wheel, resize)
• Pointer lock and gamepad APIs (later milestones)
• console.* for debugging

WebGL Mapping

WebGL calls are translated to native backend calls. The mapping is explicit:

• WebGL buffers map to native vertex/index buffers.
• WebGL textures map to native textures.
• WebGL programs map to native shader pipelines.
• WebGL state is tracked in a lightweight state cache to reduce redundant calls.

The shim does not aim for full WebGL conformance. It aims for correctness on the Three.js usage path.

Canvas and Document

• A single primary canvas is created at startup.
• document.createElement("canvas") returns an offscreen canvas object with a separate WebGL context if needed by Three.js helpers.
• DOM traversal and layout are intentionally absent.

Event Dispatch

Platform events are normalized and dispatched into the shim. The shim delivers synthetic browser-style event objects to JS listeners.