android中有canvas.drawBitmap(visiblePage, 0, 0, paint);声明
当我添加canvas.rotate(90) 时，没有效果。但是如果我写
canvas.rotate(90)
canvas.drawBitmap(visiblePage, 0, 0, paint);
我没有绘制位图。那我做错了什么？
【问题讨论】：
标签： android
你也可以试试这个
Matrix matrix = new Matrix();
matrix.postRotate(90);
Bitmap scaledBitmap = Bitmap.createScaledBitmap(bitmapOrg, width, height, true);
Bitmap rotatedBitmap = Bitmap.createBitmap(scaledBitmap, 0, 0, scaledBitmap.getWidth(), scaledBitmap.getHeight(), matrix, true);
然后您可以使用旋转后的图像在您的imageview中设置通过
imageView.setImageBitmap(rotatedBitmap);
【讨论】：
bitmap.recycle() 确定。
Bitmap source = BitmapFactory.decodeResource(this.getResources(), R.drawable.your_img);
public static Bitmap RotateBitmap(Bitmap source, float angle)
{
Matrix matrix = new Matrix();
matrix.postRotate(angle);
return Bitmap.createBitmap(source, 0, 0, source.getWidth(), source.getHeight(), matrix, true);
}
【讨论】：
If the source bitmap is immutable and the requested subset is the same as the source bitmap itself, then the source bitmap is returned and no new bitmap is created.
Kotlin
的短扩展fun Bitmap.rotate(degrees: Float): Bitmap {
val matrix = Matrix().apply { postRotate(degrees) }
return Bitmap.createBitmap(this, 0, 0, width, height, matrix, true)
}
及用法：
val rotatedBitmap = bitmap.rotate(90f)
【讨论】：
以下是在 android 中旋转或调整图像大小的代码
public class bitmaptest extends Activity {
@Override
public void onCreate(Bundle icicle) {
super.onCreate(icicle);
LinearLayout linLayout = new LinearLayout(this);
// load the origial BitMap (500 x 500 px)
Bitmap bitmapOrg = BitmapFactory.decodeResource(getResources(),
R.drawable.android);
int width = bitmapOrg.width();
int height = bitmapOrg.height();
int newWidth = 200;
int newHeight = 200;
// calculate the scale - in this case = 0.4f
float scaleWidth = ((float) newWidth) / width;
float scaleHeight = ((float) newHeight) / height;
// createa matrix for the manipulation
Matrix matrix = new Matrix();
// resize the bit map
matrix.postScale(scaleWidth, scaleHeight);
// rotate the Bitmap
matrix.postRotate(45);
// recreate the new Bitmap
Bitmap resizedBitmap = Bitmap.createBitmap(bitmapOrg, 0, 0,
width, height, matrix, true);
// make a Drawable from Bitmap to allow to set the BitMap
// to the ImageView, ImageButton or what ever
BitmapDrawable bmd = new BitmapDrawable(resizedBitmap);
ImageView imageView = new ImageView(this);
// set the Drawable on the ImageView
imageView.setImageDrawable(bmd);
// center the Image
imageView.setScaleType(ScaleType.CENTER);
// add ImageView to the Layout
linLayout.addView(imageView,
new LinearLayout.LayoutParams(
LayoutParams.FILL_PARENT, LayoutParams.FILL_PARENT
)
);
// set LinearLayout as ContentView
setContentView(linLayout);
}
}
您也可以查看此链接了解详情：http://www.anddev.org/resize_and_rotate_image_-_example-t621.html
【讨论】：
使用Java createBitmap() 方法可以通过度数。
Bitmap bInput /*your input bitmap*/, bOutput;
float degrees = 45; //rotation degree
Matrix matrix = new Matrix();
matrix.setRotate(degrees);
bOutput = Bitmap.createBitmap(bInput, 0, 0, bInput.getWidth(), bInput.getHeight(), matrix, true);
【讨论】：
我会进一步简化 comm1x 的 Kotlin 扩展函数：
fun Bitmap.rotate(degrees: Float) =
Bitmap.createBitmap(this, 0, 0, width, height, Matrix().apply { postRotate(degrees) }, true)
【讨论】：
默认情况下，旋转点是画布的 (0,0) 点，我猜你可能想围绕中心旋转它。 我做到了：
protected void renderImage(Canvas canvas)
{
Rect dest,drawRect ;
drawRect = new Rect(0,0, mImage.getWidth(), mImage.getHeight());
dest = new Rect((int) (canvas.getWidth() / 2 - mImage.getWidth() * mImageResize / 2), // left
(int) (canvas.getHeight()/ 2 - mImage.getHeight()* mImageResize / 2), // top
(int) (canvas.getWidth() / 2 + mImage.getWidth() * mImageResize / 2), //right
(int) (canvas.getWidth() / 2 + mImage.getHeight()* mImageResize / 2));// bottom
if(!mRotate) {
canvas.drawBitmap(mImage, drawRect, dest, null);
} else {
canvas.save(Canvas.MATRIX_SAVE_FLAG); //Saving the canvas and later restoring it so only this image will be rotated.
canvas.rotate(90,canvas.getWidth() / 2, canvas.getHeight()/ 2);
canvas.drawBitmap(mImage, drawRect, dest, null);
canvas.restore();
}
}
【讨论】：
如果你旋转位图，90 180 270 360 是可以的，但对于其他角度，画布会绘制不同大小的位图。
所以，最好的办法是
canvas.rotate(degree,rotateCenterPoint.x,rotateCenterPoint.y);
canvas.drawBitmap(...);
canvas.rotate(-degree,rotateCenterPoint.x,rotateCenterPoint.y);//rotate back
【讨论】：
如果您的目标是在 imageView 或文件中包含旋转图像，您可以使用 Exif 来实现。支持库现在提供：https://android-developers.googleblog.com/2016/12/introducing-the-exifinterface-support-library.html
以下是它的用法，但要实现您的目标，您必须检查库 api 文档。我只是想提示一下，旋转位图并不总是最好的方法。
Uri uri; // the URI you've received from the other app
InputStream in;
try {
in = getContentResolver().openInputStream(uri);
ExifInterface exifInterface = new ExifInterface(in);
// Now you can extract any Exif tag you want
// Assuming the image is a JPEG or supported raw format
} catch (IOException e) {
// Handle any errors
} finally {
if (in != null) {
try {
in.close();
} catch (IOException ignored) {}
}
}
int rotation = 0;
int orientation = exifInterface.getAttributeInt(
ExifInterface.TAG_ORIENTATION,
ExifInterface.ORIENTATION_NORMAL);
switch (orientation) {
case ExifInterface.ORIENTATION_ROTATE_90:
rotation = 90;
break;
case ExifInterface.ORIENTATION_ROTATE_180:
rotation = 180;
break;
case ExifInterface.ORIENTATION_ROTATE_270:
rotation = 270;
break;
}
依赖
编译“com.android.support:exifinterface:25.1.0”
【讨论】：
请注意来自 java 平台调用的 Bitmap 类型，例如 comm1x 和 Gnzlt 的答案，因为它可能返回 null。我认为如果参数可以是任何数字并使用中缀以提高可读性，它也会更加灵活，具体取决于您的编码风格。
infix fun Bitmap.rotate(degrees: Number): Bitmap? {
return Bitmap.createBitmap(
this,
0,
0,
width,
height,
Matrix().apply { postRotate(degrees.toFloat()) },
true
)
}
如何使用？
bitmap rotate 90
// or
bitmap.rotate(90)
【讨论】：