将部分图像绘制到屏幕(不加载所有内存)

Question

我想做的是在我选择的位置绘制一个图像的剪切屏幕.

我可以很容易地将其加载到位图中.然后画一个小节.

但是当图像很大时,这显然会耗尽记忆力.

我的屏幕是一个表面视图.所以有帆布等

那么如何在给定的偏移处绘制部分图像并调整大小.无需将原始内容加载到内存中

我找到了一个沿着正确的方向看的答案,但它无法正常工作.使用文件中的drawables.代码尝试如下.除了它产生的随机调整大小外,它也是不完整的.

例:

Drawable img = Drawable.createFromPath(Files.SDCARD + image.rasterName); 

    int drawWidth = (int) (image.GetOSXWidth()/(maxX - minX)) * m_canvas.getWidth();        
    int drawHeight = (int)(image.GetOSYHeight()/(maxY - minY)) * m_canvas.getHeight();

    // Calculate what part of image I need...
    img.setBounds(0, 0, drawWidth, drawHeight);

    // apply canvas matrix to move before draw...?
    img.draw(m_canvas);

Answer 1

BitmapRegionDecoder可用于加载图像的指定区域.这是一个将位图设置为两个ImageViews 的示例方法.第一个是完整图像,发送只是完整图像的一个区域:

private void configureImageViews() {

    String path = externalDirectory() + File.separatorChar
            + "sushi_plate_tokyo_20091119.png";

    ImageView fullImageView = (ImageView) findViewById(R.id.fullImageView);
    ImageView bitmapRegionImageView = (ImageView) findViewById(R.id.bitmapRegionImageView);

    Bitmap fullBitmap = null;
    Bitmap regionBitmap = null;

    try {
        BitmapRegionDecoder bitmapRegionDecoder = BitmapRegionDecoder
                .newInstance(path, false);

        // Get the width and height of the full image
        int fullWidth = bitmapRegionDecoder.getWidth();
        int fullHeight = bitmapRegionDecoder.getHeight();

        // Get a bitmap of the entire image (full plate of sushi)
        Rect fullRect = new Rect(0, 0, fullWidth, fullHeight);
        fullBitmap = bitmapRegionDecoder.decodeRegion(fullRect, null);

        // Get a bitmap of a region only (eel only)
        Rect regionRect = new Rect(275, 545, 965, 1025);
        regionBitmap = bitmapRegionDecoder.decodeRegion(regionRect, null);

    } catch (IOException e) {
        // Handle IOException as appropriate
        e.printStackTrace();
    }

    fullImageView.setImageBitmap(fullBitmap);
    bitmapRegionImageView.setImageBitmap(regionBitmap);

}

// Get the external storage directory
public static String externalDirectory() {
    File file = Environment.getExternalStorageDirectory();
    return file.getAbsolutePath();
}

结果是完整图像(顶部),只是图像的一个区域(底部):