优化 APNG 支持

[Glavo]

目前还无法工作，待修复。

[Copilot]

Pull Request Overview

This PR refactors the APNG (Animated PNG) support system to optimize image handling for animated images. The changes replace the old interface-based animation system with a new class-based approach and introduce specialized BGRA pre-multiplied pixel handling for better animation performance.

Key changes:

• Converts AnimationImage from interface to abstract class with built-in animation timeline management
• Introduces new BGRA pre-multiplied pixel format classes for more efficient animation frame handling
• Replaces the old APNG processing logic in ImageUtils with a new director-based approach

Reviewed Changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
AnimationImage.java	Converted from interface to abstract class with animation timeline management
AnimationFrame.java	New interface defining animation frame duration contract
BgraPreCanvas.java	New canvas class for BGRA pre-multiplied pixel operations
BgraPreFrame.java	New animation frame implementation extending BgraPreCanvas
BgraPreAnimationImage.java	New animation image implementation using BGRA pre-multiplied format
AnimationImageImpl.java	Refactored to extend new AnimationImage base class
BgraPreBitmapDirector.java	New director class for processing APNG files into BGRA format
Argb8888Director.java	Added exception handling to receiveFrameImage method
ImageUtils.java	Simplified APNG loading by replacing complex logic with director pattern

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[Copilot]

The argbToPre method lacks documentation explaining what 'pre' means and the purpose of the alpha premultiplication calculation.

Suggested change

	public class BgraPreCanvas {
	public class BgraPreCanvas {
	/**
	* Converts an ARGB color value to its premultiplied alpha ("pre") form.
	* <p>
	* In premultiplied alpha format, the red, green, and blue color components are
	* each multiplied by the alpha component and divided by 255. This is commonly
	* used in image compositing to simplify blending calculations and improve performance.
	* <p>
	* For example, if the original color is (A, R, G, B), the premultiplied color is
	* (A, R * A / 255, G * A / 255, B * A / 255).
	*
	* @param argb the original ARGB color value (with 8 bits per channel)
	* @return the color value in premultiplied alpha format
	*/

[Copilot]

The toString() method override simply calls super.toString() without adding any value. This override should either provide meaningful information about the canvas state or be removed.

[Copilot]

Commented-out code should be removed. These TODO comments and dead code lines make the codebase harder to maintain.

Suggested change

//return null;

[Copilot]

Debug print statement should be removed from production code.

Suggested change

//System.out.println("Frame: "+control);

[Copilot]

Commented-out code should be removed to keep the codebase clean.

Suggested change

// this.bitmapSequence.receiveDefaultImage(bitmap);

[Copilot]

TODO comment indicates uncertainty about potential issues. This should be investigated and resolved or properly documented if the concern is valid.

Suggested change

	return scanlineProcessor.cloneWithNewBitmap(header.adjustFor(control)); // TODO: is this going to be a problem?
	// It is safe to clone the scanline processor with a new bitmap for each frame,
	// as cloneWithNewBitmap creates an independent processor instance for the frame's region.
	return scanlineProcessor.cloneWithNewBitmap(header.adjustFor(control));

[Copilot]

The scaling functionality is not implemented but the method can be called when doScale is true. This will cause runtime failures when users request scaled images.

Suggested change

	throw new UnsupportedOperationException("TODO"); // TODO
	// Scale each frame to the target size
	List<BgraPreFrame> scaledFrames = new ArrayList<>(animationFrames.size());
	for (BgraPreFrame frame : animationFrames) {
	scaledFrames.add(scaleFrame(frame, targetWidth, targetHeight));
	}
	int cycleCount;
	if (animationControl != null) {
	cycleCount = animationControl.numPlays;
	if (cycleCount == 0)
	cycleCount = Timeline.INDEFINITE;
	} else
	cycleCount = Timeline.INDEFINITE;
	return new BgraPreAnimationImage(targetWidth, targetHeight, cycleCount, List.copyOf(scaledFrames));