Android-线条图问题

Question

I'm writing a small app that shows a score, and I'm having an issue when I draw the lines of the staves. At same point, the lines are not drawn properly. Here's an image to ilustrate what I'm saying:

http://imageshack.us/photo/my-images/850/y1xk.png/

This is the code:

int x = canvas.getWidth();
int y = 0;
int x_margin = 40;
int y_margin = 60;

for (int i=1; i < 51; i++) {
    canvas.drawLine(x_margin, y + y_margin, x - x_margin, y + y_margin, mLinePaint);

    if (i % 5 == 0) {

        if ((i % 10 != 0) && (tracks == 2)) {
            canvas.drawLine(x_margin, y + y_margin, x_margin, y + y_margin + 40, mLinePaint);
            canvas.drawLine(x - x_margin, y + y_margin, x - x_margin, y + y_margin + 40, mLinePaint);

            y += 40;
        }

        else {
            y += 60;
        }

    }
    else {

        canvas.drawLine(x_margin, y + y_margin, x_margin, y + y_margin + 15, mLinePaint);
        canvas.drawLine(x - x_margin, y + y_margin, x - x_margin, y + y_margin + 15, mLinePaint);

        y += 15;
    }
}

Does anyone know why is this happening?

Thanks in advance.

Answer 1

It's happening because there is a slight difference in the y at the beginning and the end of your line, make sure both y values are exactly the same.

You may also try

youCanvas.setDrawFilter(new PaintFlagsDrawFilter(Paint.ANTI_ALIAS_FLAG,Paint.DITHER_FLAG));

Answer 2

Have you checked to make sure it isn't the emulator. It may work fine if you run it on your phone.

Answer 3

I guess this is related to the conversion between the mathematical coordinates and the "real" pixel coordinates.

I would recommend to draw the line twice or more to verify the error happens always in the same points.

I would also test it on a real device, the issue is maybe related to the conversion of screen coordinates between android and the PC screen...

Good luck, this bug is not funny