Develop Reference

Android canvas draws curved semicircle

I want to draw smooth semicircle with drawArc() method. But what I get is:
RectF oval = new RectF(x - cornerRadius, y - cornerRadius, x + cornerRadius,y + cornerRadius);
canvas.drawArc(oval, start, 180, true, cornerPaint);
What's wrong with my code?

The problem has gone after I have created Paint from zero, not copying it from another Paint. Seems like another paint had parameters that affected line shape.

Rounded Rectangle with Android Canvas

I'm attempting to draw a rectangle around a custom view in Android. I mostly have it working except for one detail.
Here is my code...
Paint paint = new Paint();
paint.setColor(Color.BLACK);
paint.setStrokeWidth(14.5f);
paint.setStyle(Paint.Style.STROKE);
canvas.drawRoundRect(0, 0, getWidth(), getHeight(), 20.0f, 20.0f, paint);
And here is the resulting rectangle...
As you can see, the inside of the rectangle does have rounded corners, but the outside still draws pointed corners. How can I make it so that the outside corners are rounded as well?

You don't see corners rounded on the outside because part of the stroke is outside of the bounds of the Canvas. You can check this easily by adding a certain margin to the coordinates of the round rectangle to make sure it is drawn inside the Canvas.
In fact your best option is trying to optimize this margin depending on the selected stroke width.

How to draw segmented circle like this with certain requirements

I can't just seem to figure it out. I am trying to draw a segmented circle (what looks like circle inside a circle). However I want the segments to have specific colors and to be transparent inside the smaller circle. Preferably , I would like to make the color of the segmented lines different than the circle
Here are the solutions I had in mind:
1- Draw arc with fill color for the bigger circle and draw a circle for the small circle. 2 problems with this. First one is that the inner circle area is no longer transparent as it takes the color from the bigger one. Second problem is that the segmentation lines of the outer circle is going all the way to the center (not only to the inner circle perimeter)
2) Draw arcs for the bigger outer circle and draw circle for the inner circle. Set it to be color filled but don't show strokes. Then draw another outer circle on top with no fill just to show strokes. And then draw lines between the inner and outer circle using the calculations ( angle and radius) to determine where the lines are... Very convoluted solution, there has to be another way. Even with this solution, still have problem with the color showing in the center but maybe playing with gradient can help.
I read so much on SO but I couldn't figure the right answer as many answers would remove the control of circle parameters
HEELP!!!

#Override
public void draw(Canvas canvas) {
float size = Math.min(getWidth(),getHeight());
paint.setStrokeWidth(size/4);
paint.setStyle(Paint.Style.STROKE);
final RectF oval = new RectF(0, 0, getWidth(), getHeight());
oval.inset(size/8,size/8);
paint.setColor(Color.RED);
Path redPath = new Path();
redPath.arcTo(oval, 0, 120, true);
canvas.drawPath(redPath, paint);
paint.setColor(Color.GREEN);
Path greenPath = new Path();
greenPath.arcTo(oval, 120, 120, true);
canvas.drawPath(greenPath, paint);
paint.setColor(Color.BLUE);
Path bluePath = new Path();
bluePath.arcTo(oval, 240, 120, true);
canvas.drawPath(bluePath, paint);
paint.setStrokeWidth(2);
paint.setColor(0xff000000);
canvas.save();
for(int i=0;i<360;i+=40){
canvas.rotate(40,size/2,size/2);
canvas.drawLine(size*3/4,size/2,size,size/2,paint);
}
canvas.restore();
final RectF ovalOuter = new RectF(0, 0, getWidth(), getHeight());
ovalOuter.inset(1,1);
canvas.drawOval(ovalOuter,paint);
final RectF ovalInner = new RectF(size/4, size/4, size*3/4,size*3/4);
canvas.drawOval(ovalInner,paint);
}
I'm drawing arcs using the Path class and strokes. Style.STROKE gives arcs without filling. Stroke width is set to size/4 which is a quarter of the view. Half of that stroke width goes outside and the second half goes inside, like this:
xxxxxxxx outer border of the arc of width 5
xxxxxxxx
------------ stroke
xxxxxxxx
xxxxxxxx inner border of the arc
That's why I'm using insets - I need to offset the stroke a bit in order to fit it in the view. Without insets the arcs are cut by all four sides of the view.
And why canvas rotation? Because it's easier to rotate the canvas with built-in methods than calculate lines manually. Rotation uses trigonometric functions and quickly becomes quite complex, hard to read and error prone. Basically I'm rotating the paper and drawing straight lines.

Setting a radial gradient as the background color of a circle on canvas

I draw some circles on a canvas using .drawCircle.
I would like the fill color of that circle to be a radial gradient (or linear gradient if that's not possible).
Basically I want the circles to have some depth to them.
I'm not quite sure how to accomplish this.
I know I can define a gradient as a drawable, but is there a way to set that as the background for the drawn circle?
For example in WPF I can simply define a LinearGradientBrush and define it's stop points.
Some code for context:
Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
paint.setStyle(Paint.Style.FILL_AND_STROKE);
paint.setStrokeWidth(4);
canvas.drawCircle((float) temp_dot.get_x(),
(float) temp_dot.get_y(),
(float) temp_dot.get_radius(),
paint);
Thanks in advance for your time.

before drawing the circle, use the following code :
paint.setShader(new RadialGradient(
centerX,
centerY,
radius,
centerColor,
externalColor,
Shader.TileMode.CLAMP
));
canvas.drawCircle(..., paint);
See the RadialGradient if you want to have a more custom radial gradient.

How to draw a bar diagram on Android

I need to draw a bar diagram like the picture showing below. I am able to draw a ordinary bar diagram with filling a color on text view or some layouts. But this is a bit different.
How do I draw a bar diagram with slanting bars?
.

Try Android canvas and custom View. You can use View's onDraw method. The method provides the canvas. You should try drawArc, drawLine, etc. If your bar view contains a textView, you must use a custom viewgroup.

Do something like this in your onDraw of View.
RectF oval = new RectF();
Paint paint = new Paint();
paint.setColor(ContextCompat.getColor(context, R.color.color1));
paint.setStrokeWidth(widthOfArc);
paint.setAntiAlias(true);
paint.setStyle(Paint.Style.STROKE);
canvas.drawPath(path, yourPaint);
oval.set(x1,y1,x2,y2);
//eg:- startAngle = 10, sweepAngle = 40
canvas.drawArc(oval, startAngle, sweepAngle, false, paint);
Please read about how RectF works.
I will update the answer if I found any related blog/tutorial
Calculating start and end angle is pure Mathematics
refer this
http://www.html5canvastutorials.com/tutorials/html5-canvas-arcs/
You have to change the color and keep drawing Arc to get the result.