Android, How Can I Rotate An Arrow (image) Around A Fixed Point?
Solution 1:
This is actually pretty simple if you are using a canvas to do your drawing(as you should in your case).
Given that you know the coordinates for the point around which the image should rotate, you can do it like this:
privatevoiddoDraw(Canvas canvas){
canvas.save();
float px = ...;
float py = ...;
canvas.rotate(degrees, px, py);
arrow.draw(canvas);
canvas.restore();
}
degrees will be a integer value that you increment/decrement when the user clicks the L or R buttons. canvas.rotate takes care of the rest!
Solution 2:
You have to work with probably animation using 3d rotation in android and try to also usong Matrix Rotation ...I have bitmap code for this.........
Bitmap bmp=BitmapFactory.decodeResource(getResources(), R.drawable.bar);
Matrixmtx=newMatrix();
mtx.postRotate(180); // rotating 180 degrees clockwiseBitmaprotatedBMP= Bitmap.createBitmap(bmp, 0, 0, bmp.getWidth() ,bmp.getHeight() , mtx, true); // creating the bitmap image with new anglealso check this
Solution 3:
So there is the short answer and the long answer.
The short answer is that rotation of bitmaps and canvasses is a common function, usually called "rotate" and usually taking the point around which to rotate.
The longer answer is that all 2D and 3D graphics devolve into a trick of matrix algebra. For each point: new_x = factor_1 * old_x + factor_2 * old_y + factor_3 ...
These factors work really nicely in a matrix, and is why the matrix thing got so popular. There is a cool trick where you chain the transformations together, so you might state your problems as "take the old canvas, move it so that the touched point is the origin, rotate it, and then move it so that the origin is back at the touched point." Or Matrix m = new Matrix().postTranslate(-touch_x, -touch_y).postRotate(360/20).postTranslate(touch_x, touch_y) to rotate it by 1/20th of circle each time. Then you pass the matrix to any function that takes the "transformation" matrix.
The cool thing is that you do all the calculations for that matrix just once, and then use the same 4 multiplications on each point and a bunch of adding. In fact, this is so common that video cards and the Intel instruction set both do this stuff in hardware. You can also just multiply the resulting image again by the same matrix to get the next one.
Now, if you are really asking for the graphics hack of how do I do this in some insanely fast assembly code with no memory, the trick is to pick rotations and errors into little chains where you don't need a buffer. For example, a simple 90 degree rotation would first swap the four corners, then it would swap (upper left + 1 left goes into upper right + 1 down which goes into lower right - 1 left which goes into lower left - 1 down, which goes back into the upper left + 1). These tricks usually only matter for memory constraints.
Way too much information. Tell us more about your problem.
Solution 4:
ImageViewarrow= findViewById(/* id of your arrow */);
intwidth= arrow.getWidth();
intheight= arrow.getHeight();
newAngle = /* init it by needed angle */;
RotateAnimationanimation=newRotateAnimation(oldAngle, newAngle, width / 2, height);
oldAngle = newAngle;
animation.setDuration(200); // you may set another duration
animation.setFillAfter(true);
arrow.startAnimation(animation);
Good luck!
Solution 5:
i see this example and i adapted to work more or less like you need, please see the example for a better understanding of my code :)
import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Matrix;
import android.graphics.Paint;
import android.os.Bundle;
import android.widget.ImageView;
import android.widget.SeekBar;
publicclassTesteRotateActivityextendsActivityimplementsSeekBar.OnSeekBarChangeListener {
private ImageView myImageView;
private SeekBar seekbarRotate;
privatefloatcurScale=1F;
privatefloatcurRotate=0F;
private Bitmap bitmap;
privateint bmpHeight;
/** Called when the activity is first created. */@OverridepublicvoidonCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
myImageView = (ImageView) findViewById(R.id.imageview);
seekbarRotate = (SeekBar) findViewById(R.id.rotate);
bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.teste);//here you insert your image
bmpHeight = bitmap.getHeight();
drawMatrix();
seekbarRotate.setOnSeekBarChangeListener(this);
}
privatevoiddrawMatrix() {
Matrixmatrix=newMatrix();
Matrixmatrixb=newMatrix();
Matrixmatrixc=newMatrix();
matrix.postScale(curScale, curScale);
matrixb.setRotate(curRotate, 100, bmpHeight);
matrixc.setTranslate(100, 0);
matrix.setConcat(matrixb, matrixc);
BitmaptargetBitmap= Bitmap.createBitmap(200, bmpHeight,
bitmap.getConfig());
Canvascanvas=newCanvas(targetBitmap);
canvas.drawBitmap(bitmap, matrix, newPaint());
myImageView.setImageBitmap(targetBitmap);
}
@OverridepublicvoidonProgressChanged(SeekBar seekBar, int progress,
boolean fromUser) {
curRotate = (float) progress;
drawMatrix();
}
@OverridepublicvoidonStartTrackingTouch(SeekBar seekBar) {
}
@OverridepublicvoidonStopTrackingTouch(SeekBar seekBar) {
}
}
the xml of main
<?xml version="1.0" encoding="utf-8"?><LinearLayoutxmlns:android="http://schemas.android.com/apk/res/android"android:layout_width="fill_parent"android:layout_height="fill_parent"android:orientation="vertical" ><TextViewandroid:layout_width="fill_parent"android:layout_height="wrap_content"android:text="@string/app_name" /><SeekBarandroid:id="@+id/rotate"android:layout_width="fill_parent"android:layout_height="wrap_content"android:layout_margin="5px"android:max="360"android:progress="0" /><ImageViewandroid:id="@+id/imageview"android:layout_width="wrap_content"android:layout_height="wrap_content"android:layout_gravity="center"android:scaleType="center" /></LinearLayout>
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