Develop Reference

add a circle at the edge of arc android?

how to add small circle at the edge of arc.
and it should be also move with arc edge in the clock direction.
right now i am successfully animate the arc using changing the sweep angle.
and black dot is remaining.
below is the code of getView and animation class
--- init method and implement constructor ----
mRectF = new RectF(mWidth / 2 - 360, mHeight / 2 - 360, mWidth / 2 + 360, mHeight / 2 + 360);
#Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
//draw circle background
mPaint.setColor(getResources().getColor(R.color.timer_background_color));
canvas.drawCircle(mWidth / 2, mHeight / 2, 360, mPaint);
mPaint.setColor(getResources().getColor(R.color.actionbar_back_color));
canvas.drawArc(mRectF, mStartAnagle, mSweepAngle, false, mPaint);
}
public class TimerAnimation extends Animation{
public TimerAnimation (float startAngle, float sweepAngle, long duration) {
mStartAnagle = startAngle;
mSweepAngle = sweepAngle;
setDuration(duration);
setRepeatCount(Animation.INFINITE);
setInterpolator(new LinearInterpolator());
}
#Override
protected void applyTransformation(float interpolatedTime, Transformation t) {
if (!isComplete) {
mSweepAngle = mSweepAngle + 6;
if (mSweepAngle >= 360) {
isComplete = true;
mSweepAngle = 360;
}
} else {
mStartAnagle = mStartAnagle + 6;
mSweepAngle = mSweepAngle - 6;
if (mStartAnagle >= 360)
mStartAnagle = 0;
if (mStartAnagle == 270 || mSweepAngle <= 0) {
isComplete = false;
mSweepAngle = 0;
}
}
invalidate();
}
}

Maybe you should use Path:
Path path = new Path();
// Set the starting position of the path to (0,0).
path.moveTo(0, 0);
path.arcTo(...); //draw your arc here
path.circleTo(); //draw a small circle here at the end of arc
Also maybe you should calc the arc's end position and use as a center for small circle.

Step 1: Calculate the position of the black dot
Suggest the central position is (centerX, centerY), the position of black dot is (x,y), then,
x = radius * cos(mStartAnagle+mSweepAngle) + centerX;
y = radius * sin(mStartAnagle+mSweepAngle) + centerY;
Step 2: Draw the black dot
Suggest the dot image is R.drawable.dot ,
Bitmap bitmap = BitmapFactory.decodeResource(getResources(),R.drawable.dot)
.copy(Bitmap.Config.ARGB_8888, true);
canvas.drawBitmap(bitmap, x, y, null);

Draw rectangles on circle formula

I'm trying to draw the spectrum of an audio file on a circle. Like this:
So on the circle I just want rectangles drawn like you see on the image.
I've got this code:
public void onRender(Canvas canvas, FFTData data, Rect rect) {
canvas.drawCircle(rect.width()/2, rect.height()/2, 200, mPaint);
for (int i = 0; i < data.bytes.length / mDivisions; i++) {
byte rfk = data.bytes[mDivisions * i];
byte ifk = data.bytes[mDivisions * i + 1];
float magnitude = (rfk * rfk + ifk * ifk);
int dbValue = (int) (10 * Math.log10(magnitude));
}
}
Where FFTData is the Fast Fourier Transformation data that Android gives me. Now in my dbValue I got the strength of the signal. mDivisions is how much bars I want. Currently set on 16 because I don't know how much I can set on the circle.
I'm stuck on how I can draw the rectangle with his center on the circle line... So I want a rectangle whose height is based on the dbValue so that I get high and low rectangles. And the center must be placed on my circle line.
Can someone help me on this math formula?

Run a loop over all 360 degrees of the circle (at wanted step), and, for each point, convert Polar (this angle and the radius of the circle) coordinates into Cartesian, as described here, for instance. This way you get the location of the centre of your rectangle.
Translate the system of the coordinates, making origin to be at the wanted point on the circle line and then rotate by the circle angle at that point.
Alternatively, you can build a trapezoid by getting corners at angle +- some offset and radius +- some offset (proportional to your value to plot). It will have shorter inner edge and longer outer edge. Such trapezoids may look better if painted side by side.

i think all you have needed is a pencil and a paper and a little math and also some free time to play :-)
public class MainActivity extends Activity {
ImageView drawingImageView;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
drawingImageView = (ImageView) this.findViewById(R.id.DrawingImageView);
Paint paint;
paint = new Paint();
paint.setColor(Color.GREEN);
paint.setStyle(Paint.Style.STROKE);
paint.setStrokeWidth(16);
final Bitmap bitmap = Bitmap.createBitmap((int) getWindowManager()
.getDefaultDisplay().getWidth(), (int) getWindowManager()
.getDefaultDisplay().getHeight(), Bitmap.Config.ARGB_8888);
Canvas canvas = new Canvas(bitmap);
int centerX =400;
int centerY =400;
int R = 200;
canvas.drawCircle(centerX, centerY, R, paint);
int h = 100;
paint.setColor(Color.RED);
Path p = new Path();
p.moveTo(centerX + R - h/2, centerY);
p.lineTo(centerX + R + h/2, centerY);
canvas.drawPath(p, paint);
p = mySpectrumDrawer(centerX,centerY,R,h,15);
canvas.drawPath(p, paint);
h = 50;
p = mySpectrumDrawer(centerX,centerY,R,h,30);
canvas.drawPath(p, paint);
h = 60;
p = mySpectrumDrawer(centerX,centerY,R,h,60);
canvas.drawPath(p, paint);
h = 80;
p = mySpectrumDrawer(centerX,centerY,R,h,90);
canvas.drawPath(p, paint);
drawingImageView.setImageBitmap(bitmap);
}
private Path mySpectrumDrawer(int centerX, int centerY,int R,int height, int angel){
Path p = new Path();
int dX = (int) (R*(Math.cos(Math.toRadians(angel))));
int dY = (int) (R*(Math.sin(Math.toRadians(angel))));
int dhx = (int) (height/2*(Math.cos(Math.toRadians(angel))));
int dhy = (int) (height/2*(Math.sin(Math.toRadians(angel))));
p.moveTo(centerX + dX - dhx , centerY - dY + dhy);
p.lineTo(centerX + dX + dhx , centerY - dY - dhy);
return p;
}
}

Draw circle with different border colors Android

public static Bitmap drawCircle(int width,int height, int borderWidth) {
Bitmap canvasBitmap = Bitmap.createBitmap( width, height, Bitmap.Config.ARGB_8888);
BitmapShader shader = new BitmapShader(canvasBitmap, TileMode.CLAMP,
TileMode.CLAMP);
Paint paint = new Paint();
paint.setAntiAlias(true);
paint.setShader(shader);
paint.setShader(null);
paint.setStyle(Paint.Style.STROKE);
paint.setColor(Color.WHITE);
paint.setStrokeWidth(borderWidth);
Canvas canvas = new Canvas(canvasBitmap);
float radius = width > height ? ((float) height) / 2f : ((float) width) / 2f;
canvas.drawCircle(width / 2, height / 2, radius - borderWidth / 2, paint);
return canvasBitmap;
}
Simple this code draws a circle with white border, however I want part of the border to be black and the other part white. 40 % of it black, 60 % of it white
How can this be done?

Try this code
class MyView extends View
{
private Paint paint;
public MyView(Context context, int x, int y)
{
super(context);
paint = new Paint();
// PorterDuffXfermode xfermode = new PorterDuffXfermode(PorterDuff.Mode.CLEAR);
paint.setStyle(Paint.Style.STROKE);
paint.setColor(Color.RED);
paint.setAlpha(255);
// paint.setXfermode(xfermode);
paint.setAntiAlias(true);
// setBackgroundColor(Color.BLACK);
}
#Override
protected void onDraw(Canvas canvas)
{
canvas.drawCircle(100, 100, 50, paint);
}
}

Here a utility method for filling a circle with one color and stroking the circle border with another color.
Use the second method to pass in an existing Paint instance, e.g. to set the anti-alias flag or to prevent memory allocations during onDraw().
public static void fillCircleStrokeBorder(
Canvas c, float cx, float cy, float radius,
int circleColor, float borderWidth, int borderColor) {
fillCircleStrokeBorder(c, cx, cy, radius, circleColor, borderWidth, borderColor, new Paint());
}
public static void fillCircleStrokeBorder(
Canvas c, float cx, float cy, float radius,
int circleColor, float borderWidth, int borderColor, Paint p) {
int saveColor = p.getColor();
p.setColor(circleColor);
Paint.Style saveStyle = p.getStyle();
p.setStyle(Paint.Style.FILL);
c.drawCircle(cx, cy, radius, p);
if (borderWidth > 0) {
p.setColor(borderColor);
p.setStyle(Paint.Style.STROKE);
float saveStrokeWidth = p.getStrokeWidth();
p.setStrokeWidth(borderWidth);
c.drawCircle(cx, cy, radius - (borderWidth / 2), p);
p.setStrokeWidth(saveStrokeWidth);
}
p.setColor(saveColor);
p.setStyle(saveStyle);
}

Just draw your circle at full size with one color, then draw the circles again at the same coordinate, but with a different color and with a smaller radius, and scale down the radius however much you need to, that would be the most trivial way to do it.

How to draw ellipse's arc on android?

I want to draw an arc of ellipse in my android app.
I used this code:
#Override
protected void onDraw(Canvas canvas) {
canvas.save();
angle=45; //angle of ellipse major axis with X-axis.
startAngle=0; //start angle of arc
sweepAngle=90; //sweep angle of arc
a = 200; //major axis of ellipse
b = 100; //minor axis of ellipse
canvas.rotate(angle, center.x, center.y);
//draw the arc
canvas.drawArc(rect, startAngle - angle, sweepAngle, true, paintLine);
paintLine.setPathEffect(new DashPathEffect(new float[] { 5, 5 }, 0));
canvas.drawOval(rect, paintLine);
canvas.restore();
paintLine.setPathEffect(null);
}
I receive this shape:
The arc I need should start and end at the red point at this image:
Please tell me what mistake did I make.
Thanks.

When android draws an elliptic arc, it is as if it does so by first drawing a circular arc over the supplied sweep angle. Then it scales this circular arc so that it fits the specified ellipse. The the start and sweep-angles of the ellipse will be different from the start and sweep-angles specified. To get a wanted-angle, one must specify an actual-angle as tan(actual-angle) = (a/b)*tan(wanted-angle)
public class Main3Activity extends Activity {
#Override
public void onCreate(#Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
View view = new View(this) {
#Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
canvas.save();
float angle=45; //angle of ellipse major axis with X-axis.
// These are the wanted angles
float startAngle_ = (float)Math.toRadians(315); //start angle of arc
float endAngle_ = (float)Math.toRadians(45); //end angle of arc
float a = 200; //major axis of ellipse
float b = 100; //minor axis of ellipse
float xc = getWidth()/2f;
float yc = getHeight()/2f;
// These are the angles to use
float startAngle = (float)Math.toDegrees(
Math.atan2(a*Math.sin(startAngle_),b*Math.cos(startAngle_)));
float endAngle = (float)Math.toDegrees(
Math.atan2(a*Math.sin(endAngle_),b*Math.cos(endAngle_)));
float sweepAngle = endAngle - startAngle;
RectF rect = new RectF(xc-a,yc-b,xc+a,yc+b);
Paint paintLine = new Paint(Paint.ANTI_ALIAS_FLAG);
paintLine.setStyle(Paint.Style.STROKE);
canvas.rotate(angle,xc,yc);
//draw the arc
canvas.drawArc(rect, startAngle, sweepAngle, true, paintLine);
paintLine.setPathEffect(new DashPathEffect(new float[] { 5, 5 }, 0));
canvas.drawOval(rect, paintLine);
canvas.restore();
paintLine.setPathEffect(null);
}
};
FrameLayout.LayoutParams layout = new FrameLayout.LayoutParams(
ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.MATCH_PARENT);
addContentView(view,layout);
}
This question is nearly seven years old! About time to update the documentation?

Circle drawn on canvas doesn't match the screen

I want to draw circle in center of screen, but I'm getting something like this:
I'm using this code to draw this circle.
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
Display display = getWindowManager().getDefaultDisplay();
int width = display.getWidth();
int height = display.getHeight();
Bitmap bmp = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_4444);
Canvas c = new Canvas(bmp);
RectF rect = new RectF(0,0,width,width);
drawCircle(rect, c, width, height);
ImageView img = (ImageView) findViewById(R.id.imageView1);
img.setImageBitmap(bmp);
img.setScaleType(ScaleType.FIT_CENTER);
}
private void drawCircle(RectF rect, Canvas c, int width, int height) {
Paint paint = new Paint();
paint.setARGB(255, 255 , 10, 21);
paint.setStrokeWidth(10);
paint.setAntiAlias(true);
paint.setStrokeCap(Paint.Cap.BUTT);
paint.setStyle(Paint.Style.STROKE);
int radius;
if(width < height)
radius = width/2;
else
radius = height/2;
c.drawCircle(width/2, height/2, radius, paint);
}
I don't understand why it's cut at sides even though I use size of screen to draw it, so it should perfectly fit it.

You didn't account for the thickness of the line (strokeWidth). You drew a circle assuming it had 0 thickness, so the "actual" circle IS touching the edges of the screen, but since you used a thick paintbrush, some of the paint leaked past the edge.

you should decrease the thickness/2.
private void drawCircle(RectF rect, Canvas c, int width, int height) {
Paint paint = new Paint();
paint.setARGB(255, 255 , 10, 21);
paint.setStrokeWidth(10);
paint.setAntiAlias(true);
paint.setStrokeCap(Paint.Cap.BUTT);
paint.setStyle(Paint.Style.STROKE);
int radius;
if(width < height)
radius = width/2;
else
radius = height/2;
//this is the new line:
radius-= 5;
c.drawCircle(width/2, height/2, radius, paint);
}

Account for the StrokeWidth in the radius:
// Substract stroke width.
radius -= paint.getStrokeWidth() / 2;
c.drawCircle(width/2, height/2, radius, paint);