Develop Reference

Android Canvas Paint Arc Border

I am drawing an arc with a border by painting two arcs, one over the other the first being slightly larger.
The issue is with "slightly larger" this can end up with the border not always being even all the way round.
Both the arcs I am drawing have the same radius, I simply make it larger by adding a degree to the start and two degrees to the end (necessary to ensure the borders on either end of the arc are equal) and increasing the stroke width.
In the supplied picture the thicker border edge is the smallest I can possibly make it while it is still visible. (-1 degree off the inner arc)
I have considered drawing the arc outline with four separate calls two straight lines for either end and two arcs. This seems quite inefficient for what I want to achieve.
I am wondering if anyone has any suggestions about how else I could draw a border thats even, minimizing the number of draw/canvas rotation calls if possible.
Relevant code sample for current solution:
Paint mOutlinePaint = new Paint(Paint.ANTI_ALIAS_FLAG);
Paint mFillPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
mFillPaint.setStyle(Style.STROKE);
mFillPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC));
mFillPaint.setColor(Color.TRANSPARENT);
mFillPaint.setStrokeWidth(mValueWidth);
mOutlinePaint.setStyle(Style.STROKE);
mOutlinePaint.setStrokeWidth(mBorderWidth);
mOutlinePaint.setColor(Color.WHITE);
mRect.set(mHalfXSubRadius, mHalfYSubRadius, mHalfXAddRadius, mHalfYAddRadius);
canvas.drawArc(mRect, ARC_START-1, MAX_ARC+2, false, mOutlinePaint);
canvas.drawArc(mRect, ARC_START, MAX_ARC, false, mFillPaint);

U shouldnt make your arc bigger, instead try to draw the same sized arc (in white), X pixel right,down,up,left,corners as well (total of 8 drawings).
where X is the border size u want.
after that draw the main arc (in gray) in the middle.
psuedo code:
paint=white;
drawArc(x,y+2);
drawArc(x,y-2);
drawArc(x+2,y+2);
drawArc(x+2,y-2);
drawArc(x-2,y+2);
drawArc(x-2,y+2);
drawArc(x+2,y);
drawArc(x-2,y);
paint=gray;
drawArc(x,y);

Path . lineTo draws only half of length

Can somebody help me understand how does path.lineTo(x,y) actually work. I am trying to draw a simple straight line in a finger paint type of app. Here is an example I tried:
mPath.reset();
mPath.moveTo(0, 0);
mPath.lineTo(480, 800);
But the line goes only from 0,0 to 240, 400 - always only a half of distance as I move my finger over the screen. (the real programme has startX, startY and x,y touch coordinates instead of 0,0 & 480,800)

Maybe this piece of code will work for you:
Paint p = new Paint(Paint.ANTI_ALIAS_FLAG);
Path mPath= new Path();
mPath.moveTo(0, 0);
mPath.lineTo(480, 800);
p.setColor(0xff800000);
canvas.drawPath(mPath,p);
Also, the (480, 800) coordinate, is it still inside your screen?

The Path commands work exactly how you expect them to work and the above command should draw a line from top left to bottom righ corners in a view fully covering a 480x800 screen .
Check the follwoing:
The view covers all screen
The is no other view overlaping it
The coordinates are relative to top left coordinate of view. Check that view top left is on top left of screen
Regards.

Thanks to Goz and others who helped me truobleshoot this, it came out that Paint was doing it with this settings:
mPaint.setPathEffect(new CornerPathEffect(1000))
When this is removed or set to null, lineTo goes all the way. One just did not expect at first that Paint would do this but this corner rounding effect can shorten a straight line.

Android Rect not working

I have been trying to work on a simple code for two days now. I have tried all alterations but none seems to be working.
I am trying to draw vertical rectangles with different colors.
In the first one, I am using only one Rect variable and moving the coordinates. Here is the relevant part of the code.
Rect myRect1=new Rect();
Random colorMe=new Random();
for(int j=0;j<5;j++){
myRect1.set(myCanvas.getWidth()/5*j, 0, myCanvas.getWidth()/5*j, myCanvas.getHeight());
paint.setColor(Color.rgb(colorMe.nextInt(255), colorMe.nextInt(255), colorMe.nextInt(255)));
myCanvas.drawRect(myRect1, paint);
}
Other alteration which I tried was through an array.
Here is the code.
Rect[] myRect=new Rect[5];
Random colorMe=new Random();
for(int j=0;j<5;j++){
myRect[j].set(myCanvas.getWidth()/5*j, 0, myCanvas.getWidth()/5*j, myCanvas.getHeight());
paint.setColor(Color.rgb(colorMe.nextInt(255), colorMe.nextInt(255), colorMe.nextInt(255)));
myCanvas.drawRect(myRect[j], paint);
}
Can somebody please help me what is the problem actually there?

The first thing that seems obviously wrong (there might be more):
The minimum x-coordinate of your rectangle is myCanvas.getWidth()/5*j
The maximum x-coordinate of your rectangle is myCanvas.getWidth()/5*j
They are both the same value, so your rectangle is degenerate.
Offtopic, but very relevant: whenever you run into a problem like this, you need to break it down into smaller parts until you get it to do something. This will help you understand what's wrong:
Extract all subexpressions (like the color, and the generated x/y values) into local variables so you can easily inspect them in the debugger
Replace the random color by a predefined color (COLOR.YELLOW), to rule out the random element
Replace the caclulated rectangle by a fixed rectangle (say (10,10) - (20,20)) to rule out the coordinate calculations.
Replace the loop, to rule out the loop.

Your rect has a width of 0px. The parameters of the set() function are, in order, left/top/right/bottom. You use the same value for left and right, so the width is (right-left)=0.

Let's see your coordinates, first:
myRect1.set(myCanvas.getWidth()/5*j, 0, myCanvas.getWidth()/5*j, myCanvas.getHeight());
Top left corner has the same x coordinate as the bottom right corner, so you are drawing a rectangle with 0 width.

Add this line
myRect[j] = new Rect()
before
myRect[j].set(myCanvas.getWidth()/5*j, 0, myCanvas.getWidth()/5*j, myCanvas.getHeight());

android - animation by drawing bitmap is not smooth

I am trying to animate several shapes(paths) by drawing them on the surface holders canvas.
At first I was drawing them as paths and everything was fine, the movement was smooth.
As I increased the number of objects(shapes) the performance decreased and I made some
tests to see if instead of drawing shapes drawing bitmaps is faster. And.. drawing
bitmaps seems to be considerable faster (less computation maybe) BUT the movement is
not smooth. It looks like the bitmaps always move from pixel to pixel instead of using anti alias to, I dont know, draw states as half pixel.
The signature of the method looks like :
canvas.drawBitmap(cloudBitmap, float left, float top, Paint p);
which suggests that I should be able to draw a bitmap at 0.5f pixels.
Any idea why ?

I think it might be due to the bitmap being drawn without filtering it for smoothness. Have you set the paint to smooth the bitmap? If not, that might be your solution.
Paint paint = new Paint();
paint.setFilterBitmap(true);

How to draw a circle with a transparent middle

I am trying to draw a white circle with the following code:
mPaint.setColor(0xFFFFFFFF);
canvas.drawCircle(x, y, radius, mPaint);
But it is being displayed as a solid disk. How do I get it to just display as a circular outline with a transparent centre?
I've had a look in the help and it makes no sense to me, probably because I'm not used to the drawing terms like stroke and dither. What's wrong with background and border, eh?

I suspect you want:
mPaint.setStyle(Paint.Style.STROKE);
so that it doesn't do the filling. But then again, I've never used the Android API - this is really just a guess based on the docs :)