如何在Android中将相邻的位图绘制到画布上？

Question

I've spent all night trying to figure out why I can't draw a series of bitmaps completely adjacent to each other (with no gaps in between), using Android.

For context, I am building a spectrogram application which displays a vertical bitmap for each 'window' of audio data that comes in, providing the user with a heatmap of frequencies. At the moment I'm using pre-recorded audio so I can perform all my calculations before I have to display anything - I have an ArrayList of integer arrays, each of which represents one window's bitmap, which is drawn to a canvas using a timer thread.

I am aware that the approach below will ultimately break when the application tries to draw past the dimensions of the screen, but I am not worrying about that for now. The problem I would like to solve is that the below code results in a one-pixel (ish) gap between the drawn bitmaps, when I would actually like them to be absolutely adjacent.

This is the run() method for my timer thread:

    public void run() {
        Canvas c = null;
        try {
            c = sh.lockCanvas(null);
            synchronized(sh) {
                doDraw(c);
            }
        } finally {
            if (c!=null) {
                sh.unlockCanvasAndPost(c);
            }
        }
    }

This is the doDraw() method which draws the bitmaps, and then skips along to the end of that drawn bitmap in order to draw the next one. It simply does so by incrementing the 'windowsDrawn' field:

    private void doDraw(Canvas canvas) {
        canvas.drawBitmap(spec.getBitmapWindow(windowsDrawn), 0, 1, windowsDrawn, 0, 1, h, false, null);
        System.out.println("Windows drawn: "+windowsDrawn);
        windowsDrawn++;
    }

spec.getBitmapWindow(windowsDrawn) simply returns an integer array of pixel values for the vertical window to be drawn.

Here's a screenshot to show what I'm talking about. The image looks as if it is behind tiny prison bars and I would like to get rid of these.

Thanks!

Answer 1

I found out what I was doing wrong. The 'prison bars' effect was actually a side-effect of me writing incremental updates to the back-buffer, which was presumably being flipped every so often (hence losing some of my updates to the other buffer, giving the black vertical lines). The problem was solved by ensuring that I was instead writing to a buffer bitmap and then redrawing the entire frame each time. Incremental updates to the screen (like I was trying to do) are not allowed in Android.