Android：从位图裁剪位图并设置为 ImageView src

Posted 2023-02-25

【中文标题】Android：从位图裁剪位图并设置为 ImageView src

【英文标题】：Android: Crop Bitmap from Bitmap and set as ImageView src

【发布时间】：2015-04-25 10:34:51

【问题描述】：

我正在尝试从 spritesheet 中裁剪一个 sprite，但是裁剪后的图像不是我指定的图像的一部分。

spritesheet 包含大小为 32 x 32 像素的精灵，因此第一个精灵应该位于像素 0 到 32（水平）和 0 到 32（垂直），假设最左上角的像素是 [0, 0] .

Bitmap spritesheet = BitmapFactory.decodeResource(getResources(), R.drawable.spritesheet_32x32);
Bitmap sprite = Bitmap.createBitmap(spritesheet, 0, 0, 32, 32);

ImageView 只是一个普通的 ImageView，没有设置 src、宽度或高度。

ImageView view = (ImageView)findViewById(R.id.player1);
view.setImageBitmap(sprite);

但显示的图像只是第一个精灵的一小部分。 我监督什么？ view.setImageBitmap(sprite); 是正确的方法吗？ ImageView在设置位图之前需要固定宽高吗？

编辑：也许我应该更清楚我的布局。在一个 LinearLayout 上排列了两个 ImageView。这是 XML：

<LinearLayout
        android:orientation="horizontal"
        android:layout_
        android:layout_
        android:baselineAligned="false">
    <ImageView
        android:layout_
        android:layout_
        android:scaleX="-1"
        android:id="@+id/player1"
        android:layout_weight="1"
        android:layout_gravity="center_vertical" />
    <ImageView
        android:layout_
        android:layout_
        android:id="@+id/player2"
        android:layout_weight="1"
        android:layout_gravity="center_vertical" />
</LinearLayout>

【问题讨论】：

***.com/questions/18232034/…

【参考方案1】：

import android.graphics.Bitmap;
import android.graphics.BitmapFactory;

public class ImageResizer 

public static Bitmap decodeSampledBitmapFromFile(String filename,
    int reqWidth, int reqHeight) 
// First decode with inJustDecodeBounds=true to check dimensions
final BitmapFactory.Options
        options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;
BitmapFactory.decodeFile(filename, options);
// Calculate inSampleSize
options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);
// Decode bitmap with inSampleSize set
options.inJustDecodeBounds = false;
return BitmapFactory.decodeFile(filename, options);


public static int calculateInSampleSize(BitmapFactory.Options options,
    int reqWidth, int reqHeight) 
// BEGIN_INCLUDE (calculate_sample_size)
// Raw height and width of image
final int height = options.outHeight;
final int width = options.outWidth;
int inSampleSize = 1;

if (height > reqHeight || width > reqWidth) 

    final int halfHeight = height / 2;
    final int halfWidth = width / 2;

    // Calculate the largest inSampleSize value that is a power of 2 and keeps both
    // height and width larger than the requested height and width.
    while ((halfHeight / inSampleSize) > reqHeight
            && (halfWidth / inSampleSize) > reqWidth) 
        inSampleSize *= 2;
    

    // This offers some additional logic in case the image has a strange
    // aspect ratio. For example, a panorama may have a much larger
    // width than height. In these cases the total pixels might still
    // end up being too large to fit comfortably in memory, so we should
    // be more aggressive with sample down the image (=larger inSampleSize).

    long totalPixels = width * height / inSampleSize;

    // Anything more than 2x the requested pixels we'll sample down further
    final long totalReqPixelsCap = reqWidth * reqHeight * 2;

    while (totalPixels > totalReqPixelsCap) 
        inSampleSize *= 2;
        totalPixels /= 2;
    

return inSampleSize;
// END_INCLUDE (calculate_sample_size)
 

调用方法

Bitmap bmp = ImageResizer.decodeSampledBitmapFromFile(new  File(filePath).getAbsolutePath(), 512, 342);               

我还没有尝试过，但以下可能会通过方法参数，如imageView.getWidth()、imageView.getHeight()

【讨论】：

我必须用这个方法设置ImageView的高度和宽度吗？现在我只是传递 spritesheet 的原始尺寸，结果看起来是一样的。