Function getPlotSizeCssPx

src/core/createRenderCoordinator.ts:2308–2341

(
    canvas: SupportedCanvas,
    gridArea: GridArea
  )

  };

  const getPlotSizeCssPx = (
    canvas: SupportedCanvas,
    gridArea: GridArea
  ): { readonly plotWidthCss: number; readonly plotHeightCss: number } | null => {
    let canvasWidthCss: number;
    let canvasHeightCss: number;

    if (isHTMLCanvasElement(canvas)) {
      // HTMLCanvasElement: use getBoundingClientRect() for actual CSS dimensions
      const rect = canvas.getBoundingClientRect();
      if (!(rect.width > 0) || !(rect.height > 0)) return null;
      canvasWidthCss = rect.width;
      canvasHeightCss = rect.height;
    } else {
      // OffscreenCanvas: calculate CSS pixels from canvas dimensions divided by device pixel ratio
      const dpr = gpuContext.devicePixelRatio ?? 1.0;
      console.log('[getPlotSizeCssPx] OffscreenCanvas dimensions:', {
        canvasWidth: canvas.width,
        canvasHeight: canvas.height,
        dpr,
        calculatedCssWidth: canvas.width / dpr,
        calculatedCssHeight: canvas.height / dpr
      });
      canvasWidthCss = canvas.width / dpr;
      canvasHeightCss = canvas.height / dpr;
      if (!(canvasWidthCss > 0) || !(canvasHeightCss > 0)) return null;
    }

    const plotWidthCss = canvasWidthCss - gridArea.left - gridArea.right;
    const plotHeightCss = canvasHeightCss - gridArea.top - gridArea.bottom;
    if (!(plotWidthCss > 0) || !(plotHeightCss > 0)) return null;

    return { plotWidthCss, plotHeightCss };
  };

  const computeInteractionScalesGridCssPx = (
    gridArea: GridArea,