Runtime Notes

Content runs in JavaScriptCore, not in a browser. The type declarations (the API reference) are compiled from the engine's source, with only the APIs that really exist. The main points:

• There is no DOM and no Node.js: no document, no window; see Network for the network, Storage and Files for localStorage and files, and Audio for sound. Modules in the runtime are CommonJS require(); to use import, put your code in src/ and let the SDK bundle it (see Projects and Builds).
• DesktopEngine.system.cpuUsage() / memoryUsage() give CPU and memory usage; they need the system-info permission and throw without it.

Canvas

• Canvases have 2D, WebGL 1 and WebGL 2 (getContext('webgl2'), OpenGL ES 3.0 on ANGLE). texImage3D / texSubImage3D also take images, ImageData and canvases, with the layers top to bottom in the source image (spaced by UNPACK_IMAGE_HEIGHT, the height by default). Macs with Apple silicon have WEBGL_compressed_texture_astc.
• As in browsers, a WebGL 2 context isn't instanceof WebGLRenderingContext: check the version with instanceof WebGL2RenderingContext.
• Canvases render with Metal. On old Macs whose graphics don't support Metal, every getContext returns null and CanvasImage fails to load, so check what they return.
• Canvases have an alpha channel by default (as on the web). Widget and pet windows are transparent, so the desktop shows where nothing is drawn.
• A canvas's drawing buffer (width × height) is stretched to the size of its style, smoothly by default. For pixel art, draw 1:1 in a small buffer and set the style imageRendering: 'pixelated' to scale it up into sharp squares (the built-in pixel cat is drawn this way); 'crisp-edges' doesn't smooth when scaling down either.
• Canvases follow the scale of their display, see Displays and scale.
• The GPU gives a frame's work a few seconds at most. When a canvas takes longer (a huge draw, a shader that loops for long), macOS resets the GPU, which freezes the whole screen for a moment. The canvas' context is lost then, for good, so that it can't happen again: the canvas fires webglcontextlost (contextlost for 2D), keeps what it last showed, and draws nothing more; the context's isContextLost() returns true. Keep each frame's GPU work small, especially on large canvases. Wide shadowBlur shadows are blurred at a lower resolution, which looks the same.
• WebGL buffers, textures and shader programs are freed by gl.deleteXxx() or when the canvas is destroyed; dropping them in JavaScript doesn't delete them (they may still be bound). Programs that keep creating resources must delete them.

Not there yet

• Signing, review and an online library: content is shared by importing a .zip or a folder for now.
• APIs for the files, now-playing and window-positions permissions.
• Reading the system's audio output (music visualizers), IndexedDB.
• Native ES modules in the runtime (bundling src/ covers them for now).

Ask for what you need on GitHub.