Question

This is probably an easy one for Android experts. I am trying to draw into a Bitmap via a Canvas. I want exact colors, no anti-aliasing, and lines located at exact absolute coordinates within the Bitmap. Sometimes the lines are in the correct position and sometimes they are offset by 1 pixel. I have a feeling this has something to do with scaling. But I’m not sure. Here’s the code:

    Paint mPaint = new Paint();
    mPaint.setColor(Paint.WHITE);
    mPaint.setStrokeWidth(0);
    mPaint.setAntiAlias(false);
    mPaint.setDither(false);
    mPaint.setStyle(Paint.Style.STROKE);

    drawingContext.mycanvas.drawLine(20, 0, 10, 10, mPaint);

This actually draws a line from (19,0) to (10,9). Why?

Answer 1

I’ll answer. I had to give up on this and write a Bresenham algorithm, setting pixels one by one. That works OK for what I’m doing. I suspect a drawLine bug when drawing left to right, bottom to top lines.