重新缩放PNG的自定义方法会失去透明度

Question

嘿伙计们,我正在为支持java的手机开发j2ME游戏.我试图使用以下方法缩放透明PNG:

// method derived from a Snippet from http://snippets.dzone.com/posts/show/3257
// scales an image according to the ratios given as parameters

private Image rescaleImage(Image image, double XRatio, double YRatio)
{
    // the old height and width
    int sourceWidth = image.getWidth();
    int sourceHeight = image.getHeight();

    // what the new height and width should be
    int newWidth = (int)(XRatio * sourceWidth);
    int newHeight = (int)(YRatio * sourceHeight);

    Image newImage = Image.createImage(newWidth, newHeight);
    Graphics g = newImage.getGraphics();

    for (int y = 0; y < newHeight; y++)
    {
        for (int x = 0; x < newWidth; x++)
        {
            g.setClip(x, y, 1, 1);
            int dx = (x * sourceWidth) / newWidth;
            int dy = (y * sourceHeight) / newHeight;
            g.drawImage(image, (x - dx), (y - dy), Graphics.LEFT | Graphics.TOP);
        }
    }
    return Image.createImage(newImage);
}

它正确地缩放图像,不幸的是我似乎失去了方法返回的图像的透明度.我对这些概念相当新,任何帮助都将不胜感激!请注意,为了在任何支持 java的移动设备上正确显示,重新缩放需要在代码中完成,而不是在任何类型的图像编辑器中完成.

提前致谢!

Answer 1

感谢所有一直在为这个看似广泛存在且尚未解决的问题寻找解决方案的人。我设法在http://willperone.net/Code/codescaling.php找到了一个很好的解决方案

您只需将 createRGBImage 参数中的“false”更改为 true 即可。这会将每个像素的高阶位处理为 alpha 值的方法进行标记。这是我的实现，与上面的原始链接没有太大变化。

XRatio 和 YRatio 在画布初始化时被声明为常量，其中 XRatio = this.getWidth() （当前手机的屏幕宽度）除以原始背景图像宽度，YRatio 为 getHeight() / 原始背景图像高度。

// RESCALEIMAGE
// scales an image according to the ratios given as parameters
// derived from http://willperone.net/Code/codescaling.php

public static Image rescaleImage(Image original, double XRatio, double YRatio)
{
    // the original width and height
    int originalWidth = original.getWidth();
    int originalHeight = original.getHeight();

    // the target width and height
    int newWidth = (int)(XRatio * originalWidth);
    int newHeight = (int)(YRatio * originalHeight);

    // create and fill the pixel array from the original image
    int[] rawInput = new int[originalHeight * originalWidth];
    original.getRGB(rawInput, 0, originalWidth, 0, 0, originalWidth, originalHeight);

    // pixel array for the target image
    int[] rawOutput = new int[newWidth*newHeight];

    // YD compensates for the x loop by subtracting the width back out
    int YD = (originalHeight / newHeight) * originalWidth - originalWidth;
    int YR = originalHeight % newHeight;
    int XD = originalWidth / newWidth;
    int XR = originalWidth % newWidth;
    int outOffset= 0;
    int inOffset=  0;

    for (int y = newHeight, YE = 0; y > 0; y--)
    {
        for (int x = newWidth, XE = 0; x > 0; x--)
        {
            rawOutput[outOffset++] = rawInput[inOffset];

            inOffset += XD;
            XE += XR;

            if (XE >= newWidth)
            {
                XE -= newWidth;
                inOffset++;
            }
        }

        inOffset += YD;
        YE += YR;

        if (YE >= newHeight)
        {
            YE -= newHeight;
            inOffset += originalWidth;
        }
    }
    return Image.createRGBImage(rawOutput, newWidth, newHeight, true);
}