In my OnDraw method, I draw path into my canvas (circle with segements). All work well, now what I am not sure how to do is how can I tilt it (sort of rotation around one axis).
Basically, what I am trying to achieve is something like the tilt functionality of google map.
Here is the pseduo code:
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
// I do all the drawing here
canvas.tilt(45degrees) <-----??
}
I don't think you have to create the tilt effect within the onDraw method modifying your canvas manually. Instead use setRotationX() method on the whole View. You can also define it in xml as android:rotationX="45".
Use Canvas.concat(Matrix) with a rotation matrix, i.e.:
class MyView {
private final Matrix rotate = new Matrix();
public MyView()
{
rotate.setRotate(45.0f);
}
protected void onDraw(Canvas c)
{
super.onDraw(canvas);
canvas.save(Canvas.MATRIX_SAVE_FLAG);
canvas.concat(rotate);
canvas.restore();
}
}
Note also that you should not do any memory allocations inside onDraw() as per the android linter.
Related
I am writing a custom renderer for Xamarin.Forms. I am overriding the class ImageRenderer to do some tweaks to the image.
However, I want to overlay some parts of the image with circles, so I override the method void OnDraw(Canvas canvas).
Then I modify the Canvas a bit by drawing some circles:
protected override void OnDraw(Canvas canvas)
{
var paint = new Paint
{
Color = Color.Red
};
paint.SetStyle(Paint.Style.Fill);
foreach (var mapObject in _control.PointSource)
{
canvas.DrawCircle(mapObject.Location.X, mapObject.Location.Y, 100 / _scaleFactor, paint);
}
base.OnDraw(canvas);
}
However, everything is drawn on the background. The actual image is always on top. How can one draw circles on top of the image?
https://developer.xamarin.com/api/member/Android.Views.View.OnDraw/
In the docs they say the following:
the canvas on which the background will be drawn
So the current behaviour was expected.
I managed to fix it by moving the circle logic to the function: void Draw(Canvas canvas).
I extended the ViewPager with my class and overriden onDraw void like this:
#Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
...
}
the problem is that whatever I draw in there, it scrolls with the ViewPager, but I want it to stay on the same place. I already tried setting canvas.translate(0,0); but that didn't work.
I would really appreciate any solution how to make the draw position static.
the easy solution is to translate() your Canvas before drawing your stuff:
canvas.translate(getScrollX(), 0);
// your drawing code follows...
I hava a customized view and I draw its UI on its onDraw(Canvas canvas) method. I some case I need do some animation (anim is true)
public class GameView extends View {
//more code
#Override
protected void onDraw(Canvas canvas)
{
canvas.drawBitmap(item.getBitmap(), item.getXY().getX(), item.getXY().getY(), null);
canvas.drawBitmap(ResizedBitmapMapping.getHouse(), 0f, 0f, null);
if(amin){
canvas.save();
canvas.rotate(currentValue);
drawBall(canvas);
canvas.restore();
}
}
But the ball is very small, so only a small part of the view needs to be re-drawn. it should be a performance issue to draw the whole view. What is the right to draw such animation?
What your are looking for is Canvas.clipRect().
Here is a short video from Google that explains how it works and how to use it. Alternatively, you can invalidate only a region of a view with View.invalidate(int,int,int,int).
Is it possible to rotate an ImageButton using the onCreate() function? Or do you have to use an Animation which starts onCreate()? Because with an Animation i can see a little "flick" on Activity start...
you can use ViewCompat.setRotation(buttonInstance, rotationAngle);. From the documentation
Sets the degrees that the view is rotated around the pivot point.
You can override the onDraw() method using a custom class that extends ImageButton (which I'm sure you have).
#Override
protected void onDraw(#NonNull Canvas canvas) {
super.onDraw(canvas);
// Rotate a Bitmap
final Matrix matrix = new Matrix();
matrix.setRotate(angle, imageCenterX, imageCenterY);
canvas.drawBitmap(bitmap, matrix, null);
/*
* OR
**/
// Rotate the canvas
canvas.save(Canvas.MATRIX_SAVE_FLAG);
canvas.rotate(-angle);
canvas.drawBitmap(bitmap, left, top, null);
canvas.restore();
}
Choose one or the other solution, not both together ;)
EDIT
After some quick reflection, that could also work (not tested):
#Override
protected void onDraw(#NonNull Canvas canvas) {
canvas.rotate(-angle);
super.onDraw(canvas);
}
I'm trying to draw a few lines on a DrawView which extends SurfaceView.
in my onDraw method I loop over a list of float arrays and draw lines.
#Override
public void onDraw(final Canvas canvas) {
synchronized (lines) {
super.onDraw(canvas);
for (float[] l : lines) {
paint.setAntiAlias(true);
canvas.drawLines(l, paint);
}
}
}
I would like to animate each of these lines. I've tried to use ViewAnimator even though it's only Honeycomb and above but either I don't understand how to use it or it just isn't meant to be used with canvas.drawLine(). I've tried to use paint.setPathEffect but it doesn't seem to work at all. Anyone have any idea how to do this? I just want each line to take something like 1 second to draw one after the other.