Develop Reference

Calculating displacement with Android ImageView for a Joystick

I'm having trouble getting my program in Android Studio to properly constrain the joystick I have created. I have two ImageViews placed on top of one another, one being the joystick itself and one being the base of the joystick. Here is the code:
case R.id.analogStick:
switch(me.getAction() & MotionEvent.ACTION_MASK) {
case MotionEvent.ACTION_DOWN:
x = me.getRawX();
y = me.getRawY();
System.out.println(x);
System.out.println(y);
dx = x - v.getX();
dy = y - v.getY();
break;
case MotionEvent.ACTION_UP:
v.setX(originX);
v.setY(originY);
break;
case MotionEvent.ACTION_CANCEL:
break;
case MotionEvent.ACTION_MOVE:
float xx = originX - me.getRawX();
float yy = originY - me.getRawY();
float displacement = (float) Math.sqrt((xx * xx) + (yy * yy));
if (displacement < baseRadius) {
v.setX(me.getRawX() - dx);
v.setY(me.getRawY() - dy);
}
else {
float ratio = (float) baseRadius / displacement;
float constrainedX = originX + (me.getRawX() - originX) * ratio;
float constrainedY = originY + (me.getRawY() - originY) * ratio;
v.setX(constrainedX);
v.setY(constrainedY);
}
break;
}
break;
The main problem here is when calculating the displacement. The value turns out to be too high even when within bounds of the baseRadius, so the program always goes to the else statement, executing the constrained joystick case at all times. I get the base radius by the following formula: baseRadius = baseJoystickImage.getWidth() / 2, with baseJoystickImage being an ImageView variable. I'm not sure what could be going wrong here, any help would be appreciated.

coordinate X Y draw Android

I programmed a drawing application, I want to retrieve all the X Y of my drawing. That is to say each time I touch the screen, the coordinates x and y I put them in a two dimensional table ,
I made a toast to find out when the coordinates change, and I found that they change in the movetouch method, so I declare a table in the method and I still make a toast to see the 10 line Of my array, the toast changed co-ordination so I understood that in fact values ​​are crushed whenever the x and y change, or I am planting
public boolean onTouchEvent(MotionEvent event) {
float x = event.getX();
float y = event.getY();
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
startTouch(x, y);
invalidate();
break;
case MotionEvent.ACTION_UP:
upTouch();
invalidate();
break;
case MotionEvent.ACTION_MOVE:
moveTouche(x, y);
invalidate();
break;
}
return true;
}
Method moveTouch
public void moveTouche (float x,float y ) {
if ((canDraw)&& drawing) {
float dx = Math.abs(x - mX);
float dy = Math.abs(y - mY);
if(dx >= Tolerance || dy >= Tolerance){
path.quadTo(mX,mY,(x+mX)/2,(y+mY)/2);
mX = x ;
mY = y;
double[][] point = new double [99][2];
for (int i = 0; i < 99; i++) {
point[i][0]=x;
point[i][1]=y;
}
Toast.makeText(getContext(),"y = "+point[10][1]+" ",Toast.LENGTH_LONG).show();
}}
}

You can read as many points as you want from any path. Example how to read coordinates from the middle of path:
PathMeasure pm = new PathMeasure(myPath, false);
//coordinates will be here
float aCoordinates[] = {0f, 0f};
//get coordinates of the middle point
pm.getPosTan(pm.getLength() * 0.5f, aCoordinates, null);
You can pass any distance from the path start to get point coordinates.

Detecting Sloppy Clicks Android

I have an ImageView where I need to differentiate between a click and longclick as well as swipes. To do so I use the following code :
public boolean onTouch(View v, MotionEvent event) {
Log.d(getClass().getName(), "touch event: " + event.toString());
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
x1 = event.getX();
y1 = event.getY();
t1 = System.currentTimeMillis();
return true;
case MotionEvent.ACTION_UP:
x2 = event.getX();
y2 = event.getY();
t2 = System.currentTimeMillis();
if (x1 == x2 && y1 == y2 && (t2 - t1) < LONG_PRESS_TIMEOUT) {
//SHORT CLICK
}
The other if conditions identify hold if the time exceeeds the LONG_PRESS_TIMEOUT and swipes if the positions of the touch and release differ significantly. Anyway this works however the user needs to press and let go in the exact same point which makes it not able to identify touches which are a bit rough or sloppy, how could I alter the if condition to allow for these messy clicks but at the same time not set the offset to high so that swipes don't get mistaken as clicks.

Define a radius of 'sloppy' clicks allowed which would effectively create a circle with the center coordinates of the initial click. Then validate that the release coordinates are within that circle.
To verify that the release coordinates are within that circle you would need to calculate the distance between the center of the circle and the point and validate that it's less than the radius. (See https://math.stackexchange.com/questions/198764/how-to-know-if-a-point-is-inside-a-circle for the math involved).
Pseudocode
bool isWithinCircle(int centerX, int centerY, int x, int y, double radius)
{
var temp = pow(x - centerX, 2) + pow(y - centerY, 2);
return sqrt(temp) < r;
}
then your if condition would be:
if (isWithinCircle(x1, y1, x2, y2, radius) && (t2 - t1) < LONG_PRESS_TIMEOUT) {
//SHORT CLICK
}

Algorithm to move mouse from one point to another in a straight line

I am trying to make a small program that will move the mouse from the current position to the given position. Here is a method that i can use which will move the mouse from one point to another but without animation:
moveMouse(int x, int y);
This will move the mouse from the current coordinates to x,y on screen without animation. Now my job is to move the mouse to that coordinate, but it should also show the mouse moving one pixel at a time. I need to create a loop which moves the mouse cursor few pixels x and y at a time so that Here is what i have been thinking:
public void moveMouseAnimation(x,y){
//Integers x2 and y2 will be the current position of the mouse cursor
boolean isRunning = true;
while(isRunning){
delay(10); // <- 10 Milliseconds pause so that people can see the animation
x2 -= 1;
y2 -= 1;
moveMouse(x2,y2);
if(x2 == x && y2 == y) isRunning = false; //Ends loop
}
}
Now i need to find correct x2 and y2 values so that the mouse moves in a straight line and reaches x and y at last. Could someone help me.

You want the Bresenham's line algorithm. It is commonly used to draw a line between two points, but you, instead of drawing a line, will move the mouse along it.

Below is the code to do that. This code uses Bresenham Line Algo. For more ref on soln try http://en.wikipedia.org/wiki/Bresenham's_line_algorithm if you are looking not to have jagged lines
boolean steep = Math.abs(y1 - y0) > Math.abs(x1 - x0);
if (steep) {
int t;
// swap(x0, y0);
t = x0;
x0 = y0;
y0 = t;
// swap(x1, y1);
t = x1;
x1 = y1;
y1 = t;
}
if (x0 > x1) {
int t;
// swap(x0, x1);
t = x0;
x0 = x1;
x1 = t;
// swap(y0, y1);
t = y0;
y0 = y1;
y1 = t;
}
int deltax = x1 - x0;
int deltay = Math.abs(y1 - y0);
int error = deltax / 2;
int ystep;
int y = y0;
if (y0 < y1)
ystep = 1;
else
ystep = -1;
for (int x = x0; x < x1; x++) {
if (steep)
moveMouse(y, x);
else
moveMouse(x, y);
error = error - deltay;
if (error < 0) {
y = y + ystep;
error = error + deltax;
}
}

The problem that you are attempting to solve is that of linear interpolation, in that you have a linear function, that of a line between the starting point (x0, y0) and the ending point (x1, y1).
Luckily the solution is simple. The Wikipedia article gives examples almost exactly what you're trying to do.
http://en.wikipedia.org/wiki/Linear_interpolation

You could interpolate a straight line....basically fitting y=mx+b to the given points.

Move Minute hand in Android clock

I am trying to write a simple proof of concept app that allows a user to rotate minute hand of a clock. I am having hard time coming up with the right logic for OnTouchEvent.
So far I have the following code:
public boolean onTouchEvent(MotionEvent e) {
float x = e.getX();
float y = e.getY();
switch (e.getAction()) {
case MotionEvent.ACTION_MOVE:
//find an approximate angle between them.
float dx = x-cx;
float dy = y-cy;
double a=Math.atan2(dy,dx);
this.degree = Math.toDegrees(a);
this.invalidate();
}
return true;
}
protected void onDraw(Canvas canvas) {
super .onDraw(canvas);
boolean changed = mChanged;
if (changed) {
mChanged = false;
}
int availableWidth = getRight() - getLeft();
int availableHeight = getBottom() - getTop();
int x = availableWidth / 2;
int y = availableHeight / 2;
cx = x;
cy = y;
final Drawable dial = mDial;
int w = dial.getIntrinsicWidth() + 100;
int h = dial.getIntrinsicHeight() + 100;
boolean scaled = false;
if (availableWidth < w || availableHeight < h) {
scaled = true;
float scale = Math.min((float) availableWidth / (float) w, (float) availableHeight / (float) h);
canvas.save();
canvas.scale(scale, scale, x, y);
}
if (changed)
{
dial.setBounds(x - (w / 2), y - (h / 2), x + (w / 2), y + (h / 2));
}
dial.draw(canvas);
canvas.save();
float hour = mHour / 12.0f * 360.0f;
canvas.rotate(hour, x, y);
final Drawable hourHand = mHourHand;
if (changed) {
w = hourHand.getIntrinsicWidth() + 30;
h = hourHand.getIntrinsicHeight() + 30;
hourHand.setBounds(x - (w / 2), y - (h / 2), x + (w / 2), y + (h / 2));
}
hourHand.draw(canvas);
canvas.restore();
canvas.save();
float minute = mMinutes / 60.0f * 360.0f;
if (bearing == 0)
{
canvas.rotate(minute, x, y);
}
else
{
canvas.rotate((float)bearing, x, y);
}
final Drawable minuteHand = mMinuteHand;
if (changed) {
w = minuteHand.getIntrinsicWidth() + 30;
h = minuteHand.getIntrinsicHeight() + 30;
minuteHand.setBounds(x - w, y - h, x + w, y + h);
}
minuteHand.draw(canvas);
canvas.restore();
if (scaled) {
canvas.restore();
}
}
Then based on that, my OnDraw method rotates the minute hand to the specified "this.degree"(just calls canvas.rotate). I am assuming my math is off here. I tried to follow the example here: Calculate angle for rotation in Pie Chart, but that's still not rotating the minute hand correctly. Any help would be appreciated.

The math looks correct. Your calculations should give you the angle of the touch event, where a touch that is to the exact right of the center point should give you 0 degrees.
A few things to watch out for
Make sure that you're rotating in the correct direction. It is hard to keep this straight, and thus easy to screw it up
Make sure that you're taking into account that a value of 0 means that the minute hand should be pointing to the right. For example, if you start out with a minute hand that is pointing upwards, you would have to add/subtract 90 degrees to the result of your calculation (depending on the direction of rotation - not sure which is correct offhand)
Make sure that (cx, cy) is the center point around which you want to calculate the angle
When rotating, you'll need to either use the 3 arg Canvas.rotate(float, float, float) method, or add an additional translation seperately, to make sure that you are rotating around the correct point. Without any translation, it will rotate around (0,0) (the top left corner of the view)
More on rotation:
Rotation always happens around the "current" (0,0) point. By "current", I mean the (0,0) point after the current matrix has been applied. When you first enter onDraw, the (0,0) point should be the upper-left corner of the view. Whenever you apply a translation/scaling/etc, you will potentially change where the (0,0) point is, relative to the view.
I think something like the following should work, in regards to setting the correct center of rotation:
//first we save the initial matrix, so we can easily get
//back to this state after we're done rotating
canvas.save();
//I *think* you need to negate the center offsets here,
//because you are conceptually moving the canvas, rather
//than moving the center directly
canvas.translate(-cx, -cy);
//<perform the rotation and draw the clock hand>
//...
//and now restore the matrix back to the initial state
canvas.restore();

Your calculation is good for measuring angle for minutes hand to
rotate in corresponding quadrants in analog clock... here with little
bit changes can make either minutes or hours hand to rotate at the
touch position....call the below method in onTouch() method for action move
public float getRotationAngle(float x, float y) {
float dx = x - cx;
float dy = y - cy;
double a = Math.atan2(dy, dx);
double degree = Math.toDegrees(a)+90;
if(angle<0){
degree=degree+360;
}
return (float) degree;
}
i have this approach with as vectors concept for calculating the angle but if little bit more than your code if u want i will give that logic....