Develop Reference

How to draw a lines inside a circle angle wise?

In android I have create custom view.I have first drawn circle and now I want to draw a line angle wise within a circle. I want like this with animation.
https://drive.google.com/file/d/1Qx0MBu-77JIlQTByqGTyD-KtGKOB8naG/view?usp=sharing
I have used canvas to draw circle and lines.I have taken viewpager.If I swipe viewpager then pie graphics will rotate.
What I have done uptill now. When animating it's always start from zero:
https://drive.google.com/file/d/12mmAUOeY77jAlj_GmM3Ymcx5m34vli3X/view?usp=sharing
I have done below code:
public class PieView : View
{
int w, h, pl, pr, pt, pb, usableWidth, usableHeight, radius, cx, cy, lineLenght;
Paint paint;
public Canvas canvas;
public float firstLineangle = 0;
public float secondLineangle = 40;
public float thirdLineangle = 120;
float currentAngle,maxAngle;
public override void Draw(Canvas canvas)
{
base.Draw(canvas);
w = Width;
h = Height;
pl = PaddingLeft;
pr = PaddingRight;
pt = PaddingTop;
pb = PaddingBottom;
this.canvas = canvas;
usableWidth = w - (pl + pr);
usableHeight = h - (pt + pb);
radius = Math.Min(usableWidth, usableHeight) / 2;
cx = pl + (usableWidth / 2);
cy = pt + (usableHeight / 2);
lineLenght = radius - (pl * 2) - (pr * 2);
paint = new Paint();
paint.Color = Android.Graphics.Color.White;
paint.SetStyle(Paint.Style.Stroke);
paint.StrokeWidth = 5;
canvas.DrawCircle(cx, cy, radius - 5, paint);
Drawline(canvas, firstLineangle);
Drawline(canvas, secondLineangle);
Drawline(canvas, thirdLineangle);
PostInvalidateDelayed(500);
Invalidate();
}
public void Drawline(Canvas canvas, float angle)
{
float displacedAngle = angle - 90;
float x = cx + ((float)Math.Cos(degreesToRadians(displacedAngle)) * (radius - 5)); //convert angle to radians for x and y coordinates
float y = cy + ((float)Math.Sin(degreesToRadians(displacedAngle)) * (radius - 5));
canvas.DrawLine(cx, cy, x, y, paint); //draw a line from center point back to the point
}
public double degreesToRadians(double degrees)
{
return (degrees * Math.PI) / 180;
}
}
public class PieAnimation : Android.Views.Animations.Animation
{
private PieView pieView;
private float firstLineangle;
private float secondLineangle;
private float thirdLineangle;
public PieAnimation(PieView pieView, float firstLineangle,float secondLineangle,float thirdLineangle)
{
this.pieView = pieView;
this.firstLineangle = firstLineangle;
this.secondLineangle = secondLineangle;
this.thirdLineangle = thirdLineangle;
}
protected override void ApplyTransformation(float interpolatedTime, Transformation t)
{
pieView.firstLineangle = 0 + ((firstLineangle) * interpolatedTime);
pieView.secondLineangle = 0 + ((secondLineangle) * interpolatedTime);
pieView.thirdLineangle = 0 + ((thirdLineangle) * interpolatedTime);
pieView.RequestLayout();
}
}
public class TourPager : Java.Lang.Object, ViewPager.IOnPageChangeListener, ViewPager.IPageTransformer
{
private ViewPager mViewPager;
private float mLastOffset;
public TourView _context;
public TourPager(ViewPager viewpager, TourView context)
{
mViewPager = viewpager;
viewpager.AddOnPageChangeListener(this);
_context = context;
}
public void OnPageSelected(int position)
{
if (position == 0)
{
PieAnimation animation = new PieAnimation(_context._pieView, 0, 40, 120);
animation.Duration = (1000);
_context._pieView.StartAnimation(animation);
}
if (position==1)
{
PieAnimation animation = new PieAnimation(_context._pieView, 100, 140, 200);
animation.Duration=(1000);
_context._pieView.StartAnimation(animation);
}
if(position==2)
{
PieAnimation animation = new PieAnimation(_context._pieView, 180, 270, 10);
animation.Duration = (1000);
_context._pieView.StartAnimation(animation);
}
}

There is running GIF.
There is PieView.cs.
public class PieView:View
{
int w, h, pl, pr, pt, pb, usableWidth, usableHeight, radius, cx, cy, lineLenght;
int handTruncation, hourHandTruncation = 0;
Paint paint;
int[] numbers = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 };
Rect rect = new Rect();
public PieView(Context context) : base(context)
{
}
public PieView(Context context, IAttributeSet attrs) : base(context, attrs)
{
}
public PieView(Context context, IAttributeSet attrs, int defStyleAttr) : base(context, attrs, defStyleAttr)
{
}
public PieView(Context context, IAttributeSet attrs, int defStyleAttr, int defStyleRes) : base(context, attrs, defStyleAttr, defStyleRes)
{
}
public override void Draw(Canvas canvas)
{
base.Draw(canvas);
w = Width;
h = Height;
pl = PaddingLeft+10;
pr = PaddingRight+10;
pt = PaddingTop+10;
pb = PaddingBottom+10;
usableWidth = w - (pl + pr);
usableHeight = h - (pt + pb);
radius = Math.Min(usableWidth, usableHeight) / 2;
cx = pl + (usableWidth / 2);
cy = pt + (usableHeight / 2);
int min = Math.Min(usableWidth, usableHeight);
handTruncation = min / 20;
hourHandTruncation = min / 7;
lineLenght = radius - (pl * 2) - (pr * 2);
paint = new Paint();
paint.Color = Android.Graphics.Color.White;
paint.SetStyle(Paint.Style.Stroke);
paint.StrokeWidth = 5;
canvas.DrawCircle(cx, cy, radius , paint);
drawNumeral(canvas);
drawHands(canvas);
PostInvalidateDelayed(200);
Invalidate();
}
private void drawHands(Canvas canvas)
{
Calendar c = Calendar.Instance;
float hour = c.Get(CalendarField.HourOfDay);
hour = hour > 12 ? hour - 12 : hour;
drawHand1(canvas, (hour + c.Get(CalendarField.Minute) / 60) * 5f,true);
drawHand1(canvas, c.Get(CalendarField.Minute),false);
drawHand1(canvas, c.Get(CalendarField.Second),false);
}
private void drawNumeral(Canvas canvas)
{
paint.TextSize=50;
foreach (var number in numbers)
{
string tmp = number.ToString();
paint.GetTextBounds( tmp, 0, tmp.Length, rect); //getTextBounds(tmp, 0, tmp.length(), rect);
double angle = Math.PI / 6 * (number - 3);
int x = (int)(w / 2 + Math.Cos(angle) * radius - rect.Width() / 2);
int y = (int)(h / 2 + Math.Sin(angle) * radius + rect.Height() / 2);
canvas.DrawText(tmp, x, y, paint);
}
}
private void drawHand1(Canvas canvas, double loc, bool isHour)
{
double angle = Math.PI * loc / 30 - Math.PI / 2;
int handRadius = isHour ? radius - handTruncation - hourHandTruncation : radius - handTruncation;
canvas.DrawLine(Width / 2, Height / 2,
(float)(Width / 2 + Math.Cos(angle) * handRadius),
(float)(Height / 2 + Math.Sin(angle) * handRadius),
paint);
}
}
You can use it in MainActivity.cs
RelativeLayout relativeLayout1 = FindViewById<RelativeLayout>
(Resource.Id.relativeLayout1);
relativeLayout1.SetBackgroundColor(Color.Black);
AddContentView(new PieView(this),new ViewGroup.LayoutParams(-1,-1));

Android path disappears after changing path offset and then calling invalidate

I've managed to draw a staircase and also a smiley face (called Avatar in the code) using paths in my custom view. Id like to move the happy face up the stairs using my nextStep function. nextStep iterates the current step and then calls a function called moveToStep(int step) which offsets the Avatar to the location of the specified step. Lastly, nextStep calls this.invalidate so that onDraw gets called again in hopes that the Avatar is redrawn at the new offset. The problem is that after nextStep is called, the Avatar disappears even though the staircase still remains. I know its not offscreen because I checked the coordinates the smiley is offset to.
Custom View Code
public class StaircaseView extends View {
// setup initial color
private final int paint_color = Color.BLACK;
private int curr_step = 1;
int STEPS = 5;
private float avatar_radius;
// defines paint and canvas
private Paint DrawPaint;
private int view_width, view_height, view_size;
private Path StaircasePath, Avatar;
private float scale, side_length;
private char constrainer;
public StaircaseView(Context context, AttributeSet attrs) {
super(context, attrs);
setupPaint();
}
#Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
Log.d("StaircaseView", "onDraw called");
canvas.drawPath(StaircasePath, DrawPaint);
canvas.drawPath(Avatar, DrawPaint);
}
#Override
protected void onSizeChanged(int xNew, int yNew, int xOld, int yOld){
super.onSizeChanged(xNew, yNew, xOld, yOld);
view_height = yNew;
view_width = xNew;
view_size = Math.min(view_height, view_width);
if (view_width == view_size) {
constrainer = 'w';
} else {
constrainer = 'h';
}
scale = (float)view_size/100;
Log.i("StaircaseView", "onSizeChanged --> view width: " + String.valueOf(xNew) + ", view height: " + String.valueOf(yNew) + ", scale: " + String.valueOf(scale) + ", view size: " + String.valueOf(view_size));
float padding = 5 * scale;
StaircasePath = createStaircase(padding);
avatar_radius = 7*scale;
Avatar = createAvatar(0, 0, avatar_radius);
StaircasePath.offset(0, view_height);
moveToStep(curr_step);
}
public void nextStep() {
if (curr_step < STEPS) {
curr_step++;
} else {
curr_step = 1;
}
moveToStep(curr_step);
this.invalidate();
}
private void moveToStep(int step) {
float x = step * side_length - avatar_radius;
float y = view_height - (step - 1) * side_length - avatar_radius;
Log.i("StaircaseView", String.valueOf(x) + ", " + String.valueOf(y));
Avatar.offset(x, y);
}
// Setup paint with color and stroke styles
private void setupPaint() {
DrawPaint = new Paint();
DrawPaint.setColor(paint_color);
DrawPaint.setAntiAlias(true);
DrawPaint.setStrokeWidth(5);
DrawPaint.setStyle(Paint.Style.STROKE);
DrawPaint.setStrokeJoin(Paint.Join.ROUND);
DrawPaint.setStrokeCap(Paint.Cap.ROUND);
}
private Path createStaircase(float padding) {
if (constrainer == 'w') {
side_length = (view_size-padding)/(STEPS+1);
} else {
side_length = (view_size-padding)/STEPS;
}
Path path = new Path();
float curr_x = 0;
float curr_y = 0;
path.moveTo(curr_x, curr_y);
curr_x += side_length;
path.lineTo(curr_x, curr_y);
for(int i=0; i<STEPS; i++) {
curr_y -= side_length;
path.lineTo(curr_x, curr_y);
curr_x += side_length;
path.lineTo(curr_x, curr_y);
}
path.lineTo(curr_x, 0);
path.lineTo(0, 0);
return path;
}
private Path createShape(ArrayList<PointF> points) {
Path path = new Path();
path.moveTo(points.get(0).x, points.get(0).y);
for(int i=1; i< points.size(); i++) {
path.lineTo(points.get(i).x, points.get(i).y);
}
return path;
}
private Path createAvatar(int x, int y, float radius){
Path avatar = new Path();
float width = radius*2;
avatar.addCircle(x, y, radius, Path.Direction.CW);
avatar.addCircle(x - (radius /2), y - (radius / 5), radius/5, Path.Direction.CW);
avatar.addCircle(x + (radius / 2), y - (radius / 5), radius / 5, Path.Direction.CW);
avatar.addRect((float) x - (radius / 5), (float) y - (radius / 5), (float) x + (radius / 5), (float) y - (radius/5), Path.Direction.CCW);
return avatar;
}
}

After looking at this question decided to figure out another way to do this. So what I did was I changed my moveToStep method to return the coordinates to move the Avatar to instead of offsetting him. I then passed these coordinates to the createAvatar method as start coordinates. It worked after that.
New Code
/**
* Created by yako on 11/5/15.
*/
public class StaircaseView extends View {
// setup initial color
private final int paint_color = Color.BLACK;
private int curr_step = 1;
int STEPS = 5;
private float avatar_radius;
// defines paint and canvas
private Paint DrawPaint;
private int view_width, view_height, view_size;
private Path StaircasePath, Avatar;
private float scale, side_length;
private char constrainer;
public StaircaseView(Context context, AttributeSet attrs) {
super(context, attrs);
setupPaint();
}
#Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
Log.d("StaircaseView", "onDraw called");
canvas.drawPath(StaircasePath, DrawPaint);
canvas.drawPath(Avatar, DrawPaint);
}
#Override
protected void onSizeChanged(int xNew, int yNew, int xOld, int yOld){
super.onSizeChanged(xNew, yNew, xOld, yOld);
view_height = yNew;
view_width = xNew;
view_size = Math.min(view_height, view_width);
if (view_width == view_size) {
constrainer = 'w';
} else {
constrainer = 'h';
}
scale = (float)view_size/100;
Log.i("StaircaseView", "onSizeChanged --> view width: " + String.valueOf(xNew) + ", view height: " + String.valueOf(yNew) + ", scale: " + String.valueOf(scale) + ", view size: " + String.valueOf(view_size));
float padding = 5 * scale;
// Log.i("StaircaseView", String.valueOf(view_height/2 + padding/2));
StaircasePath = createStaircase(padding);
// Center the staircase in the view
// if (constrainer == 'w') {
// StaircasePath.offset(padding/2, view_height - (view_height - view_width - padding*2));
// } else {
// StaircasePath.offset(view_height/2 - padding/2, view_height-padding/2);
// }
avatar_radius = 7*scale;
Avatar = createAvatar(moveToStep(curr_step), avatar_radius);
StaircasePath.offset(0, view_height);
}
public void nextStep() {
if (curr_step <= STEPS) {
curr_step++;
} else {
curr_step = 1;
}
Avatar = createAvatar(moveToStep(curr_step), avatar_radius);
this.invalidate();
}
private float[] moveToStep(int step) {
float[] offset = new float[2];
offset[0] = step * side_length - avatar_radius;
offset[1] = view_height - (step - 1) * side_length - avatar_radius;
Log.i("StaircaseView", "Moving avatar to "+ String.valueOf(offset[0]) + ", " + String.valueOf(offset[1]));
return offset;
}
// Setup paint with color and stroke styles
private void setupPaint() {
DrawPaint = new Paint();
DrawPaint.setColor(paint_color);
DrawPaint.setAntiAlias(true);
DrawPaint.setStrokeWidth(5);
DrawPaint.setStyle(Paint.Style.STROKE);
DrawPaint.setStrokeJoin(Paint.Join.ROUND);
DrawPaint.setStrokeCap(Paint.Cap.ROUND);
}
private Path createStaircase(float padding) {
if (constrainer == 'w') {
side_length = (view_size-padding)/(STEPS+1);
} else {
side_length = (view_size-padding)/(STEPS+1);
}
Path path = new Path();
float curr_x = 0;
float curr_y = 0;
path.moveTo(curr_x, curr_y);
curr_x += side_length;
path.lineTo(curr_x, curr_y);
for(int i=0; i<STEPS; i++) {
curr_y -= side_length;
path.lineTo(curr_x, curr_y);
curr_x += side_length;
path.lineTo(curr_x, curr_y);
}
path.lineTo(curr_x, 0);
path.lineTo(0, 0);
return path;
}
private Path createShape(ArrayList<PointF> points) {
Path path = new Path();
path.moveTo(points.get(0).x, points.get(0).y);
for(int i=1; i< points.size(); i++) {
path.lineTo(points.get(i).x, points.get(i).y);
}
return path;
}
private Path createAvatar(float[] offset, float radius){
float x = offset[0];
float y = offset[1];
Path avatar = new Path();
float width = radius*2;
avatar.addCircle(x, y, radius, Path.Direction.CW);
avatar.addCircle(x - (radius /2), y - (radius / 5), radius/5, Path.Direction.CW);
avatar.addCircle(x + (radius / 2), y - (radius / 5), radius / 5, Path.Direction.CW);
avatar.addRect((float) x - (radius / 5), (float) y - (radius / 5), (float) x + (radius / 5), (float) y - (radius/5), Path.Direction.CCW);
return avatar;
}
}

How to draw a pie chart using RectF which will be easy to support multiple screen size in android?

Hi I am using following code to draw a pie chart in android :-
public class Chart extends View
{
private Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
private float[] value_degree;
private String[] Title_value;
RectF rectf = new RectF(50, 5, 200, 150);
Rect rect = new Rect(50, 5, 200, 150);
float temp = 0;
public Chart(Context context, float[] values, String[] heading)
{
super(context);
value_degree = new float[values.length];
Title_value = new String[heading.length];
for (int i = 0; i < values.length; i++)
{
value_degree[i] = values[i];
Log.i("abc", "" + values[i]);
Title_value[i] = heading[i];
}
}
#Override
protected void onDraw(Canvas canvas)
{
super.onDraw(canvas);
Random r;
int centerX = (rect.left + rect.right) / 2;
int centerY = (rect.top + rect.bottom) / 2;
int radius = (rect.right - rect.left) / 2;
int color;
radius *= 0.5; // 1 will put the text in the border, 0 will put the text
// in the center. Play with this to set the distance of
// your text.
for (int i = 0; i < value_degree.length; i++)
{
if (i == 0)
{
r = new Random();
color = Color.argb(100, r.nextInt(256), r.nextInt(256),
r.nextInt(256));
paint.setColor(color);
Log.i("Color", "" + color);
canvas.drawArc(rectf, temp, value_degree[i], true, paint);
paint.setColor(Color.BLACK); // set this to the text color.
paint.setTextSize(12);
/*
* paint.setTextAlign(Align.CENTER);
*/float medianAngle = (temp + (value_degree[i] / 2f))
* (float) Math.PI / 180f; // this angle will place the
// text in the center of the
// arc.
canvas.drawText(Title_value[i],
(float) (centerX + (radius * Math.cos(medianAngle))),
(float) (centerY + (radius * Math.sin(medianAngle))),
paint);
} else
{
temp += value_degree[i - 1];
r = new Random();
color = Color.argb(255, r.nextInt(256), r.nextInt(256),
r.nextInt(256));
paint.setColor(color);
Log.i("Else Color", "" + color);
canvas.drawArc(rectf, temp, value_degree[i], true, paint);
paint.setColor(Color.BLACK); // set this to the text color.
paint.setTextSize(12);
/*
* paint.setTextAlign(Align.CENTER);
*/float medianAngle = (temp + (value_degree[i] / 2f))
* (float) Math.PI / 180f; // this angle will place the
// text in the center of the
// arc.
canvas.drawText(Title_value[i],
(float) (centerX + (radius * Math.cos(medianAngle))),
(float) (centerY + (radius * Math.sin(medianAngle))),
paint);
}
}
}
}
It is showing chart in good quality in small screen sizes. But when I check it on big screen like S4 or other same screen size device it is shows a pie chart in very small size.
What should I do so it will draw perfectly on small as well as big screens?
Please help me, suggest something.
Also suggest how can I take color value to each slice in pie chart as it is assigned randomly.

Make ball bounce and eventually come to rest

I've written some code to move a ball around the screen using an orientation sensor. I wanted to get the ball to bounce when it hits the bottom of the screen, sort of like under gravity. Could somebody help out with implementing the physics in my existing code? Flipping the velocity doesn't seem to work. Here's my ball class:
package perseus.gfx.test;
import everything
public class Ball extends View {
RectF lol;
Paint paint, lpaint;
Bitmap bitmap;
Canvas canvas;
private float ballx = 150;
private float bally = 140;
private double speedx = 0;
private double speedy = 0; //ignore
private double accx, accy=0;
private float rad = 20;
private float mult = 0.5f;
private double xv, yv, xS, yS;
int width, height;
int xmax, ymax;
int xmin, ymin;
public Ball(Context context) {
super(context);
lol = new RectF();
paint = new Paint();
paint.setColor(Color.CYAN);
lpaint = new Paint();
lpaint.setColor(Color.GRAY);
}
public void moveBall() {
xv = accx * mult;
yv = accy * mult;
xS = xv * mult;
yS = yv * mult;
ballx -= xS;
bally -= yS;
// Collision detection
if (ballx + rad > xmax) {
ballx = xmax-rad;
}
else if (ballx - rad < 0) {
ballx = rad;
}
if (bally + rad > 2*ymax/3) //Shouldn't take up the whole screen
{
bally = 2*ymax/3 - rad;
}
else if (bally - rad < 0) {
bally = rad;
}
try {
Thread.sleep(20);
} catch(InterruptedException e) {}
invalidate();
}
#Override
public void onMeasure(int widthM, int heightM)
{
width = View.MeasureSpec.getSize(widthM);
height = View.MeasureSpec.getSize(heightM);
xmax = width-1;
ymax = height-1;
xmin = 0;
ymin = 0;
setMeasuredDimension(width, height);
bitmap = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
canvas = new Canvas(bitmap);
}
#Override
public void onDraw(Canvas canvas)
{
canvas.drawBitmap(bitmap, 0, 0, paint);
lol.set(ballx - rad, bally-rad, ballx + rad, bally+rad);
canvas.drawLine(0, 2*height/3, width, 2*height/3, lpaint);
canvas.drawOval(lol, paint);
canvas.drawText(xv + " " + yv, 0, height/2, lpaint);
canvas.save();
moveBall();
canvas.restore();
}
}

So the key is to just add a bit of friction, just remove a tiny bit of acceleration (negative!) at each step in moveBall(). E.g.
float friction = -0.001;
xv = accx * mult + friction;
yv = accy * mult + friction;
Then adjust the variable friction accordingly to suit your needs. For the collision you need to invert the velocity, e.g. bounce on bottom:
bally = -bally;

how to rotate text using canvas in Android

i was draw a pie chart using canvas in android and using the below code i draw a text on each slice of that pie chart (draw arc on path), now i want to draw the text length wise i.e. from center to end of the each slice,so how to rotate the arc using start and sweep angle.
p.addArc(mEventsRect, fStartAngle, fSweepAngle);
mBgPaints.setColor(iTextColor);
canvas.drawTextOnPath(sTextValue, p, fHOffSet, fVOffSet, mBgPaints);

You can try this snippet: (from: http://www.helloandroid.com/tutorials/how-use-canvas-your-android-apps-part-2)
int x = 75;
int y = 185;
paint.setColor(Color.GRAY);
paint.setTextSize(25);
String rotatedtext = "Rotated helloandroid :)";
//Draw bounding rect before rotating text:
Rect rect = new Rect();
paint.getTextBounds(rotatedtext, 0, rotatedtext.length(), rect);
canvas.translate(x, y);
paint.setStyle(Paint.Style.FILL);
canvas.drawText(rotatedtext , 0, 0, paint);
paint.setStyle(Paint.Style.STROKE);
canvas.drawRect(rect, paint);
canvas.translate(-x, -y);
paint.setColor(Color.RED);
canvas.rotate(-45, x + rect.exactCenterX(),y + rect.exactCenterY());
paint.setStyle(Paint.Style.FILL);
canvas.drawText(rotatedtext, x, y, paint);

A bit late to the party but I had to figure this one out and it's a bit simpler than what I found around. You'll already have the x and y for your text, use these to rotate the canvas
canvas.rotate(yourDegrees, x, y)
canvas.drawText(yourText, x, y, yourPaint)
canvas.rotate(-yourDegrees, x, y)
The negative sign negates the first rotation. You could swap it around to rotate in the opposite direction.
You could do this in a loop but the rotation cycle must be done each time either coordinate changes.

may be this will help you,,
here 39.5 is radius,, this will perfectly show result on mdpi screen
protected void onDraw(){
canvas.save();
PointF pf = PointOnCircle(35f, 45f, new PointF(39.5f, 39.5f));
canvas.rotate(-45, pf.x, pf.y);
canvas.drawText("67%", pf.x, pf.y, red);//23.5
canvas.restore();
canvas.save();
PointF pfa = PointOnCircle(35f, 135f, new PointF(39.5f, 39.5f));
canvas.rotate(45, pfa.x, pfa.y);
canvas.drawText("33%", pfa.x, pfa.y, red);//23.5
canvas.restore();
canvas.save();
pfa = PointOnCircle(27.5f, 225f, new PointF(39.5f, 39.5f));
canvas.rotate(-45, pfa.x, pfa.y);
canvas.drawText("45%", pfa.x, pfa.y, red);//23.5
canvas.restore();
canvas.save();
pfa = PointOnCircle(27.5f, 315f, new PointF(39.5f, 39.5f));
canvas.rotate(45, pfa.x, pfa.y);
canvas.drawText("55%", pfa.x, pfa.y, red);//23.5
canvas.restore();}
protected static final PointF PointOnCircle(float radius, float angleInDegrees, PointF origin) {
// Convert from degrees to radians via multiplication by PI/180
float x = (float) (radius * Math.cos(angleInDegrees * Math.PI / 180F)) + origin.x;
float y = (float) (radius * Math.sin(angleInDegrees * Math.PI / 180F)) + origin.y;
return new PointF(x, y);
}

Here's how i finally did it after two days of search with help of this library https://github.com/Ken-Yang/AndroidPieChart
And equations to center text done with help of my friends and alot of search
on MainActivity onCreate or oncreateView if you are using fragments:
PieChart pie = (PieChart) rootView.findViewById(R.id.pieChart);
ArrayList<Float> alPercentage = new ArrayList<Float>();
alPercentage.add(2.0f);
alPercentage.add(8.0f);
alPercentage.add(20.0f);
alPercentage.add(10.0f);
alPercentage.add(10.0f);
alPercentage.add(10.0f);
alPercentage.add(10.0f);
alPercentage.add(10.0f);
alPercentage.add(10.85f);
alPercentage.add(9.15f);
try {
// setting data
pie.setAdapter(alPercentage);
// setting a listener
pie.setOnSelectedListener(new OnSelectedLisenter() {
#Override
public void onSelected(int iSelectedIndex) {
Toast.makeText(getActivity(),
"Select index:" + iSelectedIndex,
Toast.LENGTH_SHORT).show();
}
});
} catch (Exception e) {
if (e.getMessage().equals(PieChart.ERROR_NOT_EQUAL_TO_100)) {
Log.e("kenyang", "percentage is not equal to 100");
}
}
public class PieChart extends View {
public interface OnSelectedLisenter {
public abstract void onSelected(int iSelectedIndex);
}
private OnSelectedLisenter onSelectedListener = null;
private static final String TAG = PieChart.class.getName();
public static final String ERROR_NOT_EQUAL_TO_100 = "NOT_EQUAL_TO_100";
private static final int DEGREE_360 = 360;
private static String[] PIE_COLORS = null;
private static int iColorListSize = 0;
ArrayList<Float> array;
private Paint paintPieFill;
private Paint paintPieBorder;
private Paint paintCenterCircle;
private ArrayList<Float> alPercentage = new ArrayList<Float>();
private int mCenterX = 320;
private int mCenterY = 320;
private int iDisplayWidth, iDisplayHeight;
private int iSelectedIndex = -1;
private int iCenterWidth = 0;
private int iShift = 0;
private int iMargin = 0; // margin to left and right, used for get Radius
private int iDataSize = 0;
private Canvas canvas1;
private RectF r = null;
private RectF centerCircle = null;
private float fDensity = 0.0f;
private float fStartAngle = 0.0f;
private float fEndAngle = 0.0f;
float fX;
float fY;
public PieChart(Context context, AttributeSet attrs) {
super(context, attrs);
PIE_COLORS = getResources().getStringArray(R.array.colors);
iColorListSize = PIE_COLORS.length;
array = new ArrayList<Float>();
fnGetDisplayMetrics(context);
iShift = (int) fnGetRealPxFromDp(30);
iMargin = (int) fnGetRealPxFromDp(40);
centerCircle = new RectF(200, 200, 440, 440);
// used for paint circle
paintPieFill = new Paint(Paint.ANTI_ALIAS_FLAG);
paintPieFill.setStyle(Paint.Style.FILL);
// used for paint centerCircle
paintCenterCircle = new Paint(Paint.ANTI_ALIAS_FLAG);
paintCenterCircle.setStyle(Paint.Style.FILL);
paintCenterCircle.setColor(Color.WHITE);
// used for paint border
paintPieBorder = new Paint(Paint.ANTI_ALIAS_FLAG);
paintPieBorder.setStyle(Paint.Style.STROKE);
paintPieBorder.setStrokeWidth(fnGetRealPxFromDp(3));
paintPieBorder.setColor(Color.WHITE);
Log.i(TAG, "PieChart init");
}
// set listener
public void setOnSelectedListener(OnSelectedLisenter listener) {
this.onSelectedListener = listener;
}
float temp = 0;
#Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
Log.i(TAG, "onDraw");
float centerX = (r.left + r.right) / 2;
float centerY = (r.top + r.bottom) / 2;
float radius1 = (r.right - r.left) / 2;
radius1 *= 0.5;
float startX = mCenterX;
float startY = mCenterY;
float radius = mCenterX;
float medianAngle = 0;
Path path = new Path();
for (int i = 0; i < iDataSize; i++) {
// check whether the data size larger than color list size
if (i >= iColorListSize) {
paintPieFill.setColor(Color.parseColor(PIE_COLORS[i
% iColorListSize]));
} else {
paintPieFill.setColor(Color.parseColor(PIE_COLORS[i]));
}
fEndAngle = alPercentage.get(i);
// convert percentage to angle
fEndAngle = fEndAngle / 100 * DEGREE_360;
// if the part of pie was selected then change the coordinate
if (iSelectedIndex == i) {
canvas.save(Canvas.MATRIX_SAVE_FLAG);
float fAngle = fStartAngle + fEndAngle / 2;
double dxRadius = Math.toRadians((fAngle + DEGREE_360)
% DEGREE_360);
fY = (float) Math.sin(dxRadius);
fX = (float) Math.cos(dxRadius);
canvas.translate(fX * iShift, fY * iShift);
}
canvas.drawArc(r, fStartAngle, fEndAngle, true, paintPieFill);
float angle = (float) ((fStartAngle + fEndAngle / 2) * Math.PI / 180);
float stopX = (float) (startX + (radius/2) * Math.cos(angle));
float stopY = (float) (startY + (radius/2) * Math.sin(angle));
// if the part of pie was selected then draw a border
if (iSelectedIndex == i) {
canvas.drawArc(r, fStartAngle, fEndAngle, true, paintPieBorder);
canvas.drawLine(startX, startY, stopX, stopY, paintPieFill);
canvas.restore();
}
fStartAngle = fStartAngle + fEndAngle;
}
}
#Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
// get screen size
iDisplayWidth = MeasureSpec.getSize(widthMeasureSpec);
iDisplayHeight = MeasureSpec.getSize(heightMeasureSpec);
if (iDisplayWidth > iDisplayHeight) {
iDisplayWidth = iDisplayHeight;
}
/*
* determine the rectangle size
*/
iCenterWidth = iDisplayWidth / 2;
int iR = iCenterWidth - iMargin;
if (r == null) {
r = new RectF(iCenterWidth - iR, // top
iCenterWidth - iR, // left
iCenterWidth + iR, // right
iCenterWidth + iR); // bottom
}
if (centerCircle == null) {
// centerCircle=new RectF(left, top, right, bottom);
}
setMeasuredDimension(iDisplayWidth, iDisplayWidth);
}
#Override
public boolean onTouchEvent(MotionEvent event) {
// get degree of the touch point
double dx = Math.atan2(event.getY() - iCenterWidth, event.getX()
- iCenterWidth);
float fDegree = (float) (dx / (2 * Math.PI) * DEGREE_360);
fDegree = (fDegree + DEGREE_360) % DEGREE_360;
// get the percent of the selected degree
float fSelectedPercent = fDegree * 100 / DEGREE_360;
// check which pie was selected
float fTotalPercent = 0;
for (int i = 0; i < iDataSize; i++) {
fTotalPercent += alPercentage.get(i);
if (fTotalPercent > fSelectedPercent) {
iSelectedIndex = i;
break;
}
}
if (onSelectedListener != null) {
onSelectedListener.onSelected(iSelectedIndex);
}
invalidate();
return super.onTouchEvent(event);
}
private void fnGetDisplayMetrics(Context cxt) {
final DisplayMetrics dm = cxt.getResources().getDisplayMetrics();
fDensity = dm.density;
}
private float fnGetRealPxFromDp(float fDp) {
return (fDensity != 1.0f) ? fDensity * fDp : fDp;
}
public void setAdapter(ArrayList<Float> alPercentage) throws Exception {
this.alPercentage = alPercentage;
iDataSize = alPercentage.size();
float fSum = 0;
for (int i = 0; i < iDataSize; i++) {
fSum += alPercentage.get(i);
}
if (fSum != 100) {
Log.e(TAG, ERROR_NOT_EQUAL_TO_100);
iDataSize = 0;
throw new Exception(ERROR_NOT_EQUAL_TO_100);
}
}
in your Layout:
<com.example.piecharts.PieChart
android:id="#+id/pieChart"
android:layout_width="match_parent"
android:layout_height="match_parent" >
</com.example.piecharts.PieChart>

This question is pretty old, but I figured I would write a general answer.Here I assume you want to draw your pie chart in the middle of the canvas and that you have your start and seep angles in an array.
x = canvas.getWidth/2 //Horizontal center of canvas view
y = canvas.getHeight/2 //Vertical center of canvas view
canvas.rotate(fStartAngle[i]+ fSweepAngle[i]/2, x ,y ); //Rotates canvas to a line in the middle
//of start and end of arc
canvas.translate(50f,0);//Moves the text a little out of the center of the circle (50f is arbitrary)
paintText.setStyle(Paint.Style.FILL);
canvas.drawText(rotatedtext, x, y, paintText);
//Undo the translations and rotations so that next arc can be drawn normally
canvas.translate(-50f,0);
canvas.rotate(-(temp+ value_degree[i]/2), x ,y );

it's 2023 there might be other answers out there but here is one that is sure to work
//the path where your text/paint will be drawn across
Path path = new Path();
path.addArc(mEventsRect, fStartAngle, fSweepAngle);//add this if you want your path to be drawn across the arc of your sector
//if you are using a text get the width
float textWidth = mTextPaint.measureText("text");
//this is the y co-ordinate your text will start from
int hOffset = 100;
//this is the x co-ordinate your text will start from
int vOffset = 100;
//we will be using the matrix to rotate the bunds of our current path
Matrix matrix = new Matrix();
//we will use this to get the bounds of our current path
RectF bounds = new RectF();
path.computeBounds(bounds,true);
//we are using the matrix to rotate the bound (with is the bound of the path) by 90 degrees
matrix.setRotate(90,bounds.centerX(),bounds.centerY());
the we transform the points in the path using the matrix
path.transform(matrix);
//you can now draw the text on the path
canvas.drawTextOnPath("text", path, hOffset, vOffset , mBgPaints);