Codename One 图像调整大小性能

Question

我认为将图像调整为给定尺寸（以像素为单位）以以所需尺寸显示它比使用该图像作为具有所需首选尺寸的 Label 背景更昂贵。你能证实这是真的吗？而且，如果是这样，为什么是真的？

我的意思是像下面这样使用 class 比调整包含的图像的大小更好（就性能而言）。您认为可以采用更快的方法吗？我需要以固定大小显示很多照片，但我的应用程序没有智能手机原生图库应用程序快。

/**
 * Button useful to show the given Image at the given size, without the need to
 * resize it.
 *
 * @author Francesco Galgani
 */
public class FixedSizeButton extends Button {

    private final int imageWidth;
    private final int imageHeight;
    private Image image;

    /**
     * Creates a Button displaying an Image at the given fixed size; at least
     * one of imageWidth or imageHeight must be specified.
     *
     * @param image
     * @param imageWidth in pixels, can be -1 to automatically resize
     * maintaining the aspect ratio
     * @param imageHeight in pixels, can be -1 to automatically resize
     * maintaining the aspect ratio
     */
    public FixedSizeButton(Image image, int imageWidth, int imageHeight) {
        this(image, imageWidth, imageHeight, null);
    }

    /**
     * Creates a Button displaying an Image at the given fixed size; at least
     * one of imageWidth or imageHeight must be specified.
     *
     * @param image
     * @param imageWidth in pixels, can be -1 to automatically resize
     * maintaining the aspect ratio
     * @param imageHeight in pixels, can be -1 to automatically resize
     * maintaining the aspect ratio
     * @param uiid
     */
    public FixedSizeButton(Image image, int imageWidth, int imageHeight, String uiid) {
        this(image, imageWidth, imageHeight, false, uiid);
    }

    /**
     * Creates a Button displaying an Image at the given fixed size; at least
     * one of imageWidth or imageHeight must be specified.
     *
     * @param image
     * @param imageWidth in pixels, can be -1 to automatically resize
     * maintaining the aspect ratio
     * @param imageHeight in pixels, can be -1 to automatically resize
     * maintaining the aspect ratio
     * @param scaledSmallerRatio force the image to maintain the aspect ratio
     * within the given dimension (it requires that both imageWidth and
     * imageHeight are specified)
     * @param uiid
     */
    public FixedSizeButton(Image image, int imageWidth, int imageHeight, boolean scaledSmallerRatio, String uiid) {
        if (image == null) {
            throw new IllegalArgumentException("image cannot be null");
        }
        if (imageWidth <= 0 && imageHeight <= 0) {
            throw new IllegalArgumentException("invalid imageWidth and imageHeight");
        }
        this.image = image;
        setShowEvenIfBlank(true);
        if (uiid != null) {
            super.setUIID(uiid);
        }
        if (imageWidth < 1) {
            imageWidth = image.getWidth() * imageHeight / image.getHeight();
        } else if (imageHeight < 1) {
            imageHeight = image.getHeight() * imageWidth / image.getWidth();
        }
        if (scaledSmallerRatio) {
            float hRatio = ((float) imageHeight) / ((float) image.getHeight());
            float wRatio = ((float) imageWidth) / ((float) image.getWidth());
            if (hRatio < wRatio) {
                imageWidth = (int) (image.getWidth() * hRatio);
            } else {
                imageHeight = (int) (image.getHeight() * wRatio);
            }
        }
        this.getAllStyles().setBackgroundType(Style.BACKGROUND_IMAGE_SCALED_FIT);
        this.getAllStyles().setBgImage(image);
        this.imageWidth = imageWidth;
        this.imageHeight = imageHeight;
    }

    @Override
    public Dimension calcPreferredSize() {
        int width = imageWidth + this.getStyle().getPaddingLeftNoRTL() + this.getStyle().getPaddingRightNoRTL();
        int height = imageHeight + this.getStyle().getPaddingTop() + this.getStyle().getPaddingBottom();
        return new Dimension(width, height);
    }

    /**
     * Returns the background image
     *
     * @return the bg image
     */
    @Override
    public Image getIcon() {
        return image;
    }

    @Override
    public void setText(String text) {
        throw new IllegalStateException("Not supported");
    }

    @Override
    public void setUIID(String id) {
        super.setUIID(id);
        this.getAllStyles().setBackgroundType(Style.BACKGROUND_IMAGE_SCALED_FIT);
        this.getAllStyles().setBgImage(image);
    }

}

Answer 1

性能footprint/overhead 各不相同。当您执行 Image.scaled（我假设这就是调整大小的意思...）时，图像可能会逐个像素地遍历并缩小为一个新的更小的字节数组。然后它可能会被重新编码为 PNG 或 JPEG。所有这些都是昂贵的任务。

请注意，我使用了 "might" 这个词，因为 iOS 并不总是这样做，并且在某些情况下使用硬件缩放...

当您使用绘图时，图像会作为纹理加载到 draws/scales 图像的 GPU 中。这具有零开销并且相当不错 fast.The 这里最大的缺点是 RAM，它在常规堆和 GPU 内存中都被占用。所以这是你需要做出的权衡。

Codename One 图像调整大小性能

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