glBitmap()

OpenGL Development
#1

I am trying to mimic the glBitmap() example in the Red Book, but having no luck! Here is the important bits of code:


HashMap<String, byte[]> font = new HashMap<String, byte[]>(36);

private void buildTable()
{
	font.put("A", new byte[]{(byte)0x70, (byte)0x88, (byte)0x88, (byte)0x88, (byte)0xF8, (byte)0x88, (byte)0x88, (byte)0x00});
	font.put("B", new byte[]{(byte)0xF0, (byte)0x88, (byte)0x88, (byte)0xF0, (byte)0x88, (byte)0x88, (byte)0xF0, (byte)0x00});
	font.put("C", new byte[]{(byte)0x70, (byte)0x88, (byte)0x80, (byte)0x80, (byte)0x80, (byte)0x88, (byte)0x70, (byte)0x00});
	font.put("D", new byte[]{(byte)0xF0, (byte)0x90, (byte)0x88, (byte)0x88, (byte)0x88, (byte)0x90, (byte)0xF0, (byte)0x00});
	font.put("E", new byte[]{(byte)0xF8, (byte)0x80, (byte)0x80, (byte)0xF0, (byte)0x80, (byte)0x80, (byte)0xF8, (byte)0x00});
	font.put("F", new byte[]{(byte)0xF8, (byte)0x80, (byte)0x80, (byte)0xF8, (byte)0x80, (byte)0x80, (byte)0x80, (byte)0x00});
	...
	font.put("2", new byte[]{(byte)0x70, (byte)0x88, (byte)0x08, (byte)0x10, (byte)0x20, (byte)0x40, (byte)0xF8, (byte)0x00});
	font.put("3", new byte[]{(byte)0xF8, (byte)0x10, (byte)0x20, (byte)0x10, (byte)0x08, (byte)0x88, (byte)0x70, (byte)0x00});
	font.put("4", new byte[]{(byte)0x10, (byte)0x30, (byte)0x50, (byte)0x90, (byte)0xF8, (byte)0x10, (byte)0x10, (byte)0x00});
	font.put("5", new byte[]{(byte)0xF8, (byte)0x80, (byte)0xF0, (byte)0x08, (byte)0x08, (byte)0x88, (byte)0x70, (byte)0x00});
	font.put("6", new byte[]{(byte)0x30, (byte)0x40, (byte)0x80, (byte)0xF0, (byte)0x88, (byte)0x88, (byte)0x70, (byte)0x00});
	font.put("7", new byte[]{(byte)0xF8, (byte)0x08, (byte)0x10, (byte)0x20, (byte)0x40, (byte)0x40, (byte)0x40, (byte)0x00});
	font.put("8", new byte[]{(byte)0x70, (byte)0x88, (byte)0x88, (byte)0x70, (byte)0x88, (byte)0x88, (byte)0x70, (byte)0x00});
	font.put("9", new byte[]{(byte)0x70, (byte)0x88, (byte)0x88, (byte)0x78, (byte)0x08, (byte)0x10, (byte)0x60, (byte)0x00});
}

public ByteBuffer text(String text)
{
	ByteBuffer retBuffer = ByteBuffer.allocateDirect(text.length()*8).order(ByteOrder.nativeOrder());
	byte[] letter;
	
	for(int i = 0; i < text.length(); i++)
	{
		letter = font.get(text.substring(i, i+1).toUpperCase());
		if(letter == null) letter = font.get("*");
		retBuffer.put(letter);
	}
	retBuffer.flip();
	retBuffer.rewind();
	return retBuffer;
}

private void render()
{
	// clear background
	GL11.glClear(GL11.GL_COLOR_BUFFER_BIT | GL11.GL_DEPTH_BUFFER_BIT);
	GL11.glLoadIdentity();
	GL11.glTranslatef(0.0f, 0.0f, -1f);
	
	stringBuffer = text("A");
	
	GL11.glRasterPos2f(0f, 0f);
	GL11.glBitmap(5, 8, 0, 0, 8, 0, stringBuffer);
}

This is what I get:

If I change the

stringBuffer = text("A");

to

stringBuffer = text("AAAAAAAAAA");

I get this:

What am I doing wrong?

#2

Ok, I figured it out! I needed to add

GL11.glPixelStorei(GL11.GL_UNPACK_ALIGNMENT, 1);

to my initGL() method. The I saw that it only displayed the first letter of the string and it was upside down. Turns out that OpenGL needs to have the bytes specified fromt eh bottom up, not the top down, so I flipped that and got the first letter right side up. Then I realized that it wasn’t stepping through the ByteBuffer so I added the following code to the render() method.


GL11.glRasterPos2f(0f, 0f);
stringBuffer.rewind();
for(int h = 0; h < temp.length(); h++)
{
	GL11.glBitmap(5, 8, 0, 0, 6, 0, stringBuffer);
	for(int i = 0; i < 8; i++) stringBuffer.get();
}

Now it looks like this!