My Android Tide app displays a nautical chart from a .KAP file. This file format uses a four bit palettized display system, only 10 colors are used. My app decodes the file format into an array of four bit colors. It displays a portion of this array onto the display as follows:
for (displayLineNum = 1; displayLineNum < displayHeight; displayLineNum++)
{ for (displayDotNum = 1; displayDotNum < displayWidth; displayDotNum++)
{ color = colors [lineIndex-1][dotIndex-1];
switch (color)
{ case 1: displayCanvas.drawPoint(displayDotNum, displayLineNum, color1); break;
case 2: displayCanvas.drawPoint(displayDotNum, displayLineNum, color2); break;
case 3: displayCanvas.drawPoint(displayDotNum, displayLineNum, color3); break;
case 4: displayCanvas.drawPoint(displayDotNum, displayLineNum, color4); break;
case 5: displayCanvas.drawPoint(displayDotNum, displayLineNum, color5); break;
case 6: displayCanvas.drawPoint(displayDotNum, displayLineNum, color6); break;
case 7: displayCanvas.drawPoint(displayDotNum, displayLineNum, color7); break;
case 8: displayCanvas.drawPoint(displayDotNum, displayLineNum, color8); break;
case 9: displayCanvas.drawPoint(displayDotNum, displayLineNum, color9); break;
case 10: displayCanvas.drawPoint(displayDotNum, displayLineNum, color10); break;
default: displayCanvas.drawPoint(displayDotNum, displayLineNum, color1); break;
}
}
}
display_area.setImageBitmap(displayBitmap);
There are 10 paint colors pre set with the RGB codes necessary for display. But each pixel has to be drawn individually with the displayCanvas.drawPoint function. This works but it is DOG SLOW. I would rather pre set the palette codes on the other side of the display call, and pass in the palette values instead. This would run a lot faster but I can't find a way to do this with the display calls available. There are Android functions to evaluate an image to get a palette for it, etc but I cant see how to efficiently display a palettized image. Each pixel is getting blown up for a four bit pixel code to a sixteen bit RGB565 code in order to pass in a normal bitmap. How else could I do this, thank you.
To define the pixels of a Bitmap, you shouldn't use a Canvas because it adds an extra layer and is inefficient. You should deal with the Bitmap object directly. There are two ways to do that.
The setPixel() method allows to set the color of a pixel.
Example:
Bitmap bm = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
for(int x = 0; x < width; x++)
{
for(int y = 0; y < height; y++)
bm.setPixel(x, y, Color.BLUE);
}
To avoid the overhead of calling setPixel() a large number of times, you can build an array with the pixel colors and pass it directly to createBitmap(). This is probably the most efficient way.
Example:
int length = width * height;
int[] colors = new int[length];
for(int i = 0; i < length; i++)
colors[i] = Color.BLUE;
Bitmap bm = Bitmap.createBitmap(colors, width, height, Bitmap.Config.ARGB_8888);