Question

I try to draw a line with the width depending on the density.
The problem is that I can not make setStrokeWidth() method paint the width I want.
Here is the code:

...    
private void init(){
        paint = new Paint();
        paint.setStyle(Paint.Style.STROKE);
        paint.setColor(Color.BLACK);        
        paint.setStrokeWidth(3);    
    }

@Override
    protected void onDraw(Canvas canvas){
        canvas.drawLine(0, 0, getWidth(), 0, paint);        
    }
...

The above code displays a line with 2px width both on mdpi and hdpi screens.
How can I make paint to draw the line with the specified width?
Where does 1.5 scale factor come from?

Answer 1

You are drawing at the absolute top of the canvas, making only half the line visible, that is why it ends up 2 px wide. To see the entire line, move it down a bit.

To create a density dependent value you can use the following code:

float scale = getResources().getDisplayMetrics().density;
int sizeInDp = (int) (desiredWidthInPx*scale + 0.5f);

paint.setStrokeWidth(sizeInDp);