Perf: Optimize background opacity calculation for high-res images

[KSSJW]

优化了高分辨率背景图的透明度计算

测试材料

• 来源：Minecraft Wallpaper - Chaos Cubed Drop
• 分辨率：2560 x 1440

实况

修改前

1.mp4

修改后

2.mp4

[KSSJW]

/gemini review

[gemini-code-assist]

Code Review

This pull request modifies the background image opacity rendering in Themes.java by replacing the pixel-by-pixel loop with a Canvas and Canvas.snapshot() approach. However, the review feedback highlights critical issues with this change: calling Canvas.snapshot() on a background thread will throw an IllegalStateException, and hardcoding the canvas size to 800x480 degrades image quality. The reviewer suggests using batch pixel operations via PixelReader.getPixels() and PixelWriter.setPixels() to achieve thread safety, high performance, and full resolution. Additionally, suggestions are provided to update the imports accordingly and to check for a null PixelReader to prevent potential NullPointerExceptions.

Important

The consumer version of Gemini Code Assist on GitHub is being sunset. Starting June 18, 2026, new organization installations will be blocked, and all code review activity will officially cease on July 17, 2026.
For more details on the timeline and next steps, please review the Help Documentation.

[Wulian233]

现在流畅非常多

[KSSJW]

感觉 PixelFormat、PixelReader 和 PixelWriter 没有 SnapshotParameters、Canvas 和 GraphicsContext 那么快（

[KSSJW]

/gemini review

[gemini-code-assist]

Code Review

This pull request optimizes the background opacity calculation in Themes.java by scaling the image to a fixed 800x480 resolution using AWT/Swing utilities and performing bulk pixel operations. The reviewer pointed out that this approach introduces unnecessary AWT dependencies and causes image blurriness on high DPI screens. They recommended performing bulk pixel operations directly on the original JavaFX image to maintain image quality and performance without AWT overhead, providing a code suggestion to achieve this.

Important

The consumer version of Gemini Code Assist on GitHub is being sunset. Starting June 18, 2026, new organization installations will be blocked, and all code review activity will officially cease on July 17, 2026.
For more details on the timeline and next steps, please review the Help Documentation.

[Glavo]

之后我打算重构壁纸相关功能，用 StackPane 在主界面后面叠一层 ImageView 来实现背景，这样调整不透明度就不需要重写图片了。

[KSSJW]

之后我打算重构壁纸相关功能，用 StackPane 在主界面后面叠一层 ImageView 来实现背景，这样调整不透明度就不需要重写图片了。

确实，不然方法怎么优化本质上还是在重新绘制图像（
当前背景不能直接设置透明度，应该是ReadOnlyObjectWrapper<Background>类型的问题（？）

private static final ReadOnlyObjectWrapper<Background> background = new ReadOnlyObjectWrapper<>(
            new Background(new BackgroundFill(Color.WHITE, CornerRadii.EMPTY, Insets.EMPTY)));

private static void refreshBackgroundOpacity() {
    ...
    LoadedBackground refreshed;
    refreshed = new LoadedBackground.Image(...)
    ...
    loadedBackground = refreshed;
    background.set(refreshed.background());
}