Develop Reference

How to check if a touch event is outside or inside of a region in android

I have an image of a basketball pitch or any other pitch, and I want to check if the user checks outside or inside of 3 points area how can I achieve this? Shall I use predefined points of x,y?

Well if that area is a perfect half-circle, which I think it is, then the formula would be quite easy. You get X and Y coordinates of a touch event whichever way you prefer (that's not the issue here, use GestureDetector for example). I'll just give you an example of the isIn3PointArea() method:
private boolean isIn3PointArea(float touchX, float touchY, float centerX, float centerY, float r){
float x = touchX - centerX;
float y = touchY - centerY;
return (touchX > centerX && Math.sqrt(x*x+y*y) < r);
}
Explanation:
This is the method for the left 3 point area, for the right one you'd just need to swap out > operator with < in the touchX > centerX part. It's quite logical, your point needs to be less than r (which is the radius of your circle) from the center point (which has x coordinate of 0) and y, well whatever you give it, I'm not quite sure what you use to draw the court. Also it needs the touchX to be right of ( greater than > ) the centerX because if it's not, the touch is out of the field. The reverse logic applies to the right 3 point area.
The only thing that's up to you to deduce is what parameters to give to this method (you didn't share any code so I cannot know what your radius is or what are the coordinates of the court).

You can do this using x and y but believe me it will get very messy very soon. What I would suggest is use different image Views for different regions and add onClickListeners to the each of them . For this you will have to ask for different assets for each element in your court.

Draw on custom view with zoom not working properly

When drawing on view without zoom it works fine. See the screenshot
But when zooming and then drawing on view It is slightly up or down. See the screenshot
Here is my code for Custom View http://www.paste.org/78026 and for zoom http://www.paste.org/78027 and my xml http://www.paste.org/78028
Please can you tell me where I am wrong

Finally after lot of searching I found how to get relative X,Y when View is zoomed. It may be helpful to someone
// Get the values of the matrix
float[] values = new float[9];
matrix.getValues(values);
// values[2] and values[5] are the x,y coordinates of the top left corner of the drawable image, regardless of the zoom factor.
// values[0] and values[4] are the zoom factors for the image's width and height respectively. If you zoom at the same factor, these should both be the same value.
// event is the touch event for MotionEvent.ACTION_UP
float relativeX = (event.getX() - values[2]) / values[0];
float relativeY = (event.getY() - values[5]) / values[4];

Simultaneous rotation, translation, and scaling of bitmap in android canvas

I'm trying to show a picture, which can be zoomed and panned, and that rotates with a compass reading. With the code below, all three actions kind of work, but they influence each other.
Here is what I want to achieve:
1. Rotate around the center of the screen
2. Scale leaving the same part of the picture in the center
3. Pan to the desired spot in the picture
Here is what is actually happening with the code below:
1. Rotation works as intended, around the center of the screen
2. Scaling works, but it scales around the center of the picture
3. Translation only works as intended if angle is zero, otherwise it's moving in a wrong direction
// the center of the view port
float centerX = screen.right/2;
float centerY = screen.bottom/2;
Matrix m = new Matrix();
m.preRotate(angle, centerX, centerY);
m.preScale(mScaleFactor, mScaleFactor, centerX, centerY);
// scaling the amount of translation,
// rotating the translation here gave crazy results
float x = mPosX / mScaleFactor;
float y = mPosY / mScaleFactor;
m.preTranslate(x, y);
canvas.drawBitmap(pic, m, null);
If I translate first, and later rotate, the translation works as intended but the rotation is not around the center of the view port anymore.
How can I apply all three transformations, without them influencing each other?

I'm not sure about the scaling around the centre of the image, but as for the translation being in the wrong direction is it not as a consequence of you rotating the image but not the translations? Maybe try something like this:
float x = (mPosX*(cos(angle) + sin(angle)) / mScaleFactor;
float y = (mPosY*(cos(angle) - sin(angle)) / mScaleFactor;
m.preTranslate(x, y);
Also does the matrix object have a method to apply an affine transformation directly? Because then you won't need to think about the order of operations.
The affine transformation might look something like this:
M = |mScaleFactor*cos(angle) sin(angle) x|
| -sin(angle) mScaleFactor*cos(angle) y|
| 0 0 1|
But this will rotate around the corner of the image so you need to use the preTranslate() function first like so:
Mt.preTranslate(-centerX,-centerY);
And APPLY Mt to pic before applying M and then after you need to apply -Mt

Canvas Zoom goes to point (0,0)

I am having a problem in zooming the canvas. I have made a customized view in which I am drawing relationship diagrams now when I zoom out the canvas in goes to the position (0,0). I have seen different threads and questions but could not find appropriate answer.
What i am doing in onDraw Method is.
canvas.scale(mScaleFactor, mScaleFactor);
I have also seen the canvas.scale(x, y, px, py) method but i do not know how to get the pivot points of x and y.
public boolean onScale(ScaleGestureDetector detector) {
mScaleFactor *= detector.getScaleFactor();
// Don't let the object get too small or too large.
mScaleFactor = Math.max(0.4f, Math.min(mScaleFactor, 5.0f));
if(mScaleFactor>=1)
mScaleFactor=1f;
invalidate();
return true;
}

The pivot points are basically the point that your canvas will be transformed around, so scaling with a pivot of 0,0 makes it shrink towards that point.
using the following method you can change the pivot point to wherever you want it:
canvas.scale(x, y, px, py);
Now for the new stuff:
If you want your canvas to be scaled towards its centre, you will just have to know the point in the middle of your canvas:
float cX = canvas.getWidth()/2.0f; //Width/2 gives the horizontal centre
float cY = canvas.getHeight()/2.0f; //Height/2 gives the vertical centre
And then you can scale it using those coordinates:
canvas.scale(x, y, cX, cY);

Take a look at these two answers, they describe the problem and its solutions very well.
Android Bitmap/Canvas offset after scale
Scaling image of ImageView while maintaining center point in same place

centered zoom in custom view - calculating canvas coordinates

I am working on my first "real" Android application, a graphical workflow editor. The drawing is done in a custom class, that is a subclass of View.At the moment my elements are rectangles, which are drawn on a canvas. To detect actions on elements I compare the coordinates and check for elements on the touch location.
To implement a zoom gesture I tried http://android-developers.blogspot.com/2010/06/making-sense-of-multitouch.html
With the 4 argument canvas.scale(...) function the centered zooming works well, but I lose the ability to calculate the canvas coordinates using the offset with mPosX and mPosY to detect if the touch after a zoom is on an element.
I tried to change the example in the blogpost above to center the canvas on the zoom gesture with:
canvas.save();
canvas.translate(mPosX, mPosY);
canvas.scale(mScaleFactor, mScaleFactor, mScalePivotX, mScalePivotY);
//drawing ....
canvas.restore();
I did not find any examples on how this could be done without losing the reference offset to calculate the coordinates. Is there an easy workaround? I tried to calculate the offset with the gesture center and the scaling factor, but failed :/
I have seen that other examples which use an ImageView often use a Matrix to transform the image. Could this be done with a custom View and a Canvas? If yes, how can I get the x and y offset to check the coordinates?
Also, if my ideas are completely wrong, I would be very happy to see some examples on how this is done properly.
Thx! ;)

Perhaps the following code will help you to calculate coordinates with the gesture center and the scaling factor. I use this method in my class representing opengl-sprite.
void zoom(float scale, PointF midPoint) {
if (zoomFactor == MAX_ZOOM_FACTOR && scale > 1) return;
if (zoomFactor == MIN_ZOOM_FACTOR && scale < 1) return;
zoomFactor *= scale;
x = (x - midPoint.x) * scale + midPoint.x;
y = (y - height + midPoint.y) * scale + height - midPoint.y;
if (zoomFactor >= MAX_ZOOM_FACTOR) {
zoomFactor = MAX_ZOOM_FACTOR;
} else if (zoomFactor < MIN_ZOOM_FACTOR) {
zoomFactor = MIN_ZOOM_FACTOR;
x = 0;
y = 0;
}
}
X and Y coordinates are processed in different ways, because of distinction between directions of opengl coordinate system (right and up) and midPoint's coordinate system (right and down). midPoint is taken from MotionEvents coordinates.
All other operations are understandable, i think.
Hope it will help you.