OpenTK OpenGL Drawing text - vb.net

Question

I am trying to learn how to do OpenGL using OpenTK and I can successfully draw polygons, circles, and triangles so far but my next question is how to draw text? I have looked at the example on their homepage which was in C# and I translated it to VB .NET.
It currently just draws a white rectangle so I was hoping that someone could spot an error in my code or suggest another way to draw text. I will just list my paint event.
Paint event:
GL.Clear(ClearBufferMask.ColorBufferBit)
GL.Clear(ClearBufferMask.DepthBufferBit)
Dim text_bmp As Bitmap
Dim text_texture As Integer
text_bmp = New Bitmap(ClientSize.Width, ClientSize.Height)
text_texture = GL.GenTexture()
GL.BindTexture(TextureTarget.Texture2D, text_texture)
GL.TexParameter(TextureTarget.Texture2D, TextureParameterName.TextureMagFilter, All.Linear)
GL.TexParameter(TextureTarget.Texture2D, TextureParameterName.TextureMinFilter, All.Linear)
GL.TexImage2D(TextureTarget.Texture2D, 0, PixelInternalFormat.Rgba, text_bmp.Width, text_bmp.Height, 0 _
, PixelFormat.Bgra, PixelType.UnsignedByte, IntPtr.Zero)
Dim gfx As Graphics
gfx = Graphics.FromImage(text_bmp)
gfx.DrawString("TEST", Me.Font, Brushes.Red, 0, 0)
Dim data As Imaging.BitmapData
data = text_bmp.LockBits(New Rectangle(0, 0, text_bmp.Width, text_bmp.Height), Imaging.ImageLockMode.ReadOnly, System.Drawing.Imaging.PixelFormat.Format32bppArgb)
GL.TexImage2D(TextureTarget.Texture2D, 0, PixelInternalFormat.Rgba, Width, Height, 0, PixelFormat.Bgra, PixelType.UnsignedByte, data.Scan0)
text_bmp.UnlockBits(data)
GL.MatrixMode(MatrixMode.Projection)
GL.LoadIdentity()
GL.Ortho(0, width, Height, 0, -1, 1)
GL.Enable(EnableCap.Texture2D)
GL.Enable(EnableCap.Blend)
GL.BlendFunc(BlendingFactorSrc.One, BlendingFactorDest.OneMinusSrcAlpha)
GL.Begin(BeginMode.Quads)
GL.TexCoord2(0.0F, 1.0F)
GL.Vertex2(0.0F, 0.0F)
GL.TexCoord2(1.0F, 1.0F)
GL.Vertex2(1.0F, 0.0F)
GL.TexCoord2(1.0F, 0.0F)
GL.Vertex2(1.0F, 1.0F)
GL.TexCoord2(0.0F, 0.0F)
GL.Vertex2(0.0F, 1.0F)
GL.End()
GlControl1.SwapBuffers()

Answer 1

You'll get a white rectangle if your card doesn't support NPOT (non-power-of-two) texture sizes. Try testing by setting the bitmap size to e.g. 256x256.

Answer 2

That is an ok method. If you plan to draw lots of text or even a medium amount, that will absolutely destroy performance. What you want to do is look into a program called BMFont:
www.angelcode.com/products/bmfont/‎
What this does is create a texture atlas of text, along with an xml file with the positions, width and height and offsets of every letter. You start off by reading that xml file, and loading each character into a class, with the various values. Then you simply make a function that you pass a string which binds the atlas, than depending on the letters in the string, draws a quad with texture coordinates that vary on the xml data. So you might make a:
for each _char in string
create quad according to xml size
assign texture coordinates relative to xml position
increase position so letters don't draw on top of each other
There are tutorials in other languages on the BMFont website which can be helpful.