adjust Bitmap width and height in MapField in BlackBerry

Question

I am drawing circles around a location point in the MapField like in the code given below:

 public void drawCircleMap(int [] radius)
{
   int i = 0;
    Graphics graphics = null;
    int x2,y2;
    bmparr = new Bitmap[radius.length];
    for(int j=0;j<radius.length;j++)
    {
                XYPoint fieldOut = new XYPoint();
                convertWorldToField(mPoints[1], fieldOut);
                x2 = fieldOut.x;
                y2 = fieldOut.y;
                bmparr[i] = new Bitmap(getWidth(), getHeight());
                bmparr[i].createAlpha(Bitmap.ALPHA_BITDEPTH_8BPP);
                graphics = Graphics.create( bmparr[i]);
                graphics.setColor(Color.BLUE);
                graphics.drawEllipse(x2, y2, x2+radius[j], y2, x2,y2+radius[j], 0, 360);
                graphics.fillEllipse(x2, y2, x2+radius[j], y2, x2,y2+radius[j], 0, 360);
                i++;
    }

}

protected void paint(Graphics graphics) {
    super.paint(graphics);

    for(int i =0 ;i < bmparr.length;i++)
    {
        graphics.setGlobalAlpha(100);
        graphics.drawBitmap(0, 0,  bmparr[i].getWidth(), bmparr[i].getHeight(), bmparr[i], 0, 0);
    }

}

I want to draw 4 circles, now as i draw more number of circles, the map seems to fade out, Can someone please tell me how i could solve this issue?

Answer 1

I have solved this problem by drawing a transparent background for every bitmap:

bmparr = new Bitmap[radius.length];
for(int j=0;j<radius.length;j++)
{
  XYPoint fieldOut = new XYPoint();
  convertWorldToField(mPoints[1], fieldOut);
  x2 = fieldOut.x;
  y2 = fieldOut.y;
  bmparr[i] = new Bitmap(getWidth(), getHeight());
  bmparr[i].createAlpha(Bitmap.ALPHA_BITDEPTH_8BPP);
  int[] argb = new int[getWidth() * getHeight()];
  bmparr[i].getARGB(argb, 0, getWidth(), 0, 0, getWidth(), getHeight());
  for(int k = 0; k < argb.length; k++)
  {
      argb[k] = 0x00000000;
  }
  bmparr[i].setARGB(argb, 0, getWidth(), 0, 0, getWidth(), getHeight());
  graphics = Graphics.create( bmparr[i]);
  graphics.setColor(Color.BLUE);
  graphics.drawEllipse(x2, y2, x2+radius[j], y2, x2,y2+radius[j], 0, 360);
  graphics.fillEllipse(x2, y2, x2+radius[j], y2, x2,y2+radius[j], 0, 360);
  i++;
}

Answer 2

I believe your problem is with alpha blending. You are drawing each image, one on top of the other, with approximately 50% alpha. So, the first radius "covers" half of the existing pixel intensity. Then the next radius covers half of the remaining intensity, or 75% of the original intensity. And so on... each time you draw an image, it is covering up more and more of the original intensity.

If you want all of your circles to have a common intensity, you will need to re-think your approach. For example, consider drawing all of your circles in a single bitmap before drawing that on top of the map. Or consider having each larger circle leave a 100% transparent "hole" where the smaller circles will be.