Fix flipy

[xiaoiver]

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[gemini-code-assist]

Code Review

This pull request implements dynamic viewport height calculation for Y-coordinate flipping in WebGPU render passes. Feedback focuses on simplifying the logic for determining the flip height and maintaining proper encapsulation by avoiding string-indexed access to private class members.

[gemini-code-assist]

The logic for determining the viewport flip height can be simplified by using the nullish coalescing operator and leveraging the already populated internal state (this.gfxColorAttachment and this.gfxDepthStencilAttachment).

Also, note that accessing this.device['swapChainHeight'] via string indexing is a bypass of TypeScript's private access modifier. It would be better to expose this value through a public getter in the Device_WebGPU class to maintain proper encapsulation.

    const level0 = this.gfxColorAttachmentLevel[0] ?? 0;
    const firstColor = this.gfxColorAttachment[0];
    if (firstColor) {
      this._viewportFlipHeight = Math.max(1, firstColor.height >>> level0);
    } else if (this.gfxDepthStencilAttachment) {
      this._viewportFlipHeight = Math.max(1, this.gfxDepthStencilAttachment.height >>> 0);
    } else {
      this._viewportFlipHeight = this.device['swapChainHeight'];
    }

[gemini-code-assist]

Accessing the private property swapChainHeight via string indexing here also breaks encapsulation. Since _viewportFlipHeight is guaranteed to be initialized in setRenderPassDescriptor (which is called by beginRenderPass), you can likely rely on it being set or use a safer fallback that doesn't bypass access modifiers.