jassub/src/worker/renderers/canvas-base.ts

The Fastest JavaScript SSA/ASS Subtitle Renderer For Browsers

export class CanvasRendererBase {
  canvas
  _scheduledResize?: { width: number, height: number }

  constructor (canvas: OffscreenCanvas) {
    this.canvas = canvas
  }

  resizeCanvas (width: number, height: number) {
    // WebGL doesn't allow 0-sized canvases
    if (!width || !height) return
    if (this.canvas.width === width && this.canvas.height === height) return

    this._scheduledResize = { width, height }
  }

  applyScheduledResize () {
    // Apply a scheduled resize right before rendering, so the resize and the
    // first draw happen in one call and the resized buffer is never presented
    // on its own.
    if (!this._scheduledResize) return

    const resize = this._scheduledResize
    this._scheduledResize = undefined
    this.canvas.width = resize.width
    this.canvas.height = resize.height
    return resize
  }
}