I'm going crazy trying to draw some text over an OpenGL window using OpenTK! I followed some of the tutorials around but I can't make it work, when I enable the texture where the text is drawn, then I just have a white window and the QUAD I'm drawing for test just disappears. If someone has the time to check the code, it is below. I can also send my test program to check it out faster. Thanks in advance for any help on this.
using System;
using System.Drawing;
using System.Drawing.Imaging;
using System.Windows.Forms;
using OpenTK.Graphics.OpenGL;
using System.Diagnostics;
namespace WindowsFormsApplication1
{
public partial class Form1 : Form
{
Bitmap textBmp;
int textTexture = -1;
public Form1()
{
InitializeComponent();
}
private void Form1_Load(object sender, EventArgs e)
{
if (!glControl1.Context.IsCurrent)
{
glControl1.MakeCurrent();
}
GL.MatrixMode(MatrixMode.Projection);
GL.LoadIdentity();
GL.Ortho(0, glControl1.Width, 0, glControl1.Height, -1000, 1000);
GL.Scale(1, 1, 1);
GL.Viewport(0, 0, glControl1.Width, glControl1.Height);
GL.ClearColor(Color.White);
// Better point and line drawing
GL.Hint(HintTarget.PointSmoothHint, HintMode.Nicest);
GL.Hint(HintTarget.LineSmoothHint, HintMode.Nicest);
GL.BlendFunc(BlendingFactorSrc.One, BlendingFactorDest.OneMinusSrcAlpha);
GL.Enable(EnableCap.PointSmooth);
GL.Enable(EnableCap.LineSmooth);
GL.Enable(EnableCap.Blend);
// Hide stuff behind in 3D
GL.Enable(EnableCap.DepthTest);
// Enable the texture
GL.Enable(EnableCap.Texture2D);
// Create Bitmap and OpenGL texture
textBmp = new Bitmap((int)glControl1.Width, (int)glControl1.Height);
textTexture = GL.GenTexture();
GL.BindTexture(TextureTarget.Texture2D, textTexture);
GL.TexParameter(TextureTarget.Texture2D, TextureParameterName.TextureMinFilter, (int)TextureMinFilter.Linear);
GL.TexParameter(TextureTarget.Texture2D, TextureParameterName.TextureMagFilter, (int)TextureMagFilter.Linear);
GL.TexImage2D(TextureTarget.Texture2D, 0, PixelInternalFormat.Rgba, textBmp.Width, textBmp.Height, 0,
OpenTK.Graphics.OpenGL.PixelFormat.Rgba, PixelType.UnsignedByte, IntPtr.Zero);
ErrorCode errorCode = GL.GetError();
Debug.Assert(errorCode == ErrorCode.NoError, "OpenTK error!");
}
private void glControl1_Paint(object sender, PaintEventArgs e)
{
ErrorCode errorCode;
GL.Clear(ClearBufferMask.ColorBufferBit | ClearBufferMask.DepthBufferBit | ClearBufferMask.StencilBufferBit);
GL.PushMatrix();
GL.Color3(Color.Black);
GL.Begin(PrimitiveType.Quads);
GL.Vertex3(10, 10, 10);
GL.Vertex3(40, 10, 10);
GL.Vertex3(40, 50, 10);
GL.Vertex3(10, 50, 10);
GL.End();
if (textBmp != null)
{
using (Graphics gfx = Graphics.FromImage(textBmp))
{
gfx.Clear(Color.Transparent);
gfx.DrawString("text", new Font("Arial", 10), Brushes.Black, new PointF(textBmp.Width / 2, textBmp.Height));
}
BitmapData data = textBmp.LockBits(new Rectangle(0, 0, textBmp.Width, textBmp.Height), ImageLockMode.ReadOnly, System.Drawing.Imaging.PixelFormat.Format32bppArgb);
GL.TexImage2D(TextureTarget.Texture2D, 0, PixelInternalFormat.Rgba, (int)glControl1.Width, (int)glControl1.Height, 0,
OpenTK.Graphics.OpenGL.PixelFormat.Bgra, PixelType.UnsignedByte, data.Scan0);
textBmp.UnlockBits(data);
errorCode = GL.GetError();
Debug.Assert(errorCode == ErrorCode.NoError, "OpenTK error!");
GL.Begin(PrimitiveType.Quads);
GL.TexCoord2(0f, 1f); GL.Vertex2(0f, 0f);
GL.TexCoord2(1f, 1f); GL.Vertex2(1f, 0f);
GL.TexCoord2(1f, 0f); GL.Vertex2(1f, 1f);
GL.TexCoord2(0f, 0f); GL.Vertex2(0f, 1f);
GL.End();
}
errorCode = GL.GetError();
Debug.Assert(errorCode == ErrorCode.NoError, "OpenTK error!");
glControl1.SwapBuffers();
}
}
}
Answer
Ok, I finally managed to make it work.
On initialization I just did:
if (!control.Context.IsCurrent)
{
control.MakeCurrent();
}
GL.Ortho(0, controlWidth, 0, controlHeight, -1000, 1000);
GL.Scale(1, -1, 1); // I work with a top/left image and openGL is bottom/left
GL.Viewport(0, 0, controlWidth, controlHeight);
GL.ClearColor(Color.White);
GL.Hint(HintTarget.PointSmoothHint, HintMode.Nicest);
GL.Hint(HintTarget.LineSmoothHint, HintMode.Nicest);
GL.BlendFunc(BlendingFactorSrc.One, BlendingFactorDest.OneMinusSrcAlpha);
GL.BlendFunc(BlendingFactorSrc.SrcAlpha, BlendingFactorDest.OneMinusSrcAlpha);
GL.PolygonMode(MaterialFace.Front, PolygonMode.Line);
GL.Enable(EnableCap.PointSmooth);
GL.Enable(EnableCap.LineSmooth);
GL.Enable(EnableCap.Blend);
GL.Enable(EnableCap.DepthTest);
GL.ShadeModel(ShadingModel.Smooth);
GL.Enable(EnableCap.AutoNormal);
bmp = new Bitmap(width, height, System.Drawing.Imaging.PixelFormat.Format32bppArgb);
gfx = Graphics.FromImage(bmp);
gfx.TextRenderingHint = System.Drawing.Text.TextRenderingHint.AntiAlias;
texture = GL.GenTexture();
GL.BindTexture(TextureTarget.Texture2D, texture);
GL.TexParameter(TextureTarget.Texture2D, TextureParameterName.TextureMinFilter, (int)TextureMinFilter.Linear);
GL.TexParameter(TextureTarget.Texture2D, TextureParameterName.TextureMagFilter, (int)TextureMagFilter.Linear);
GL.TexImage2D(TextureTarget.Texture2D, 0, PixelInternalFormat.Rgba, bmp.Width, bmp.Height, 0,
OpenTK.Graphics.OpenGL.PixelFormat.Rgba, PixelType.UnsignedByte, IntPtr.Zero);
Then to write text in the bitmap:
gfx.DrawString(text, font, brush, new PointF(x, y));
And to render:
if (!control.Context.IsCurrent)
{
control.MakeCurrent();
}
GL.Clear(ClearBufferMask.ColorBufferBit | ClearBufferMask.DepthBufferBit);
GL.MatrixMode(MatrixMode.Modelview);
GL.Enable(EnableCap.Texture2D);
GL.BindTexture(TextureTarget.Texture2D, Texture);
GL.Begin(PrimitiveType.Quads);
GL.TexCoord3(0.0f, 0.0f, 0f); GL.Vertex3(0f, 0f, 0f);
GL.TexCoord3(1.0f, 0.0f, 0f); GL.Vertex3(realWidth, 0f, 0f);
GL.TexCoord3(1.0f, 1.0f, 0f); GL.Vertex3(realWidth, realHeight, 0f);
GL.TexCoord3(0.0f, 1.0f, 0f); GL.Vertex3(0f, realHeight, 0f);
GL.End();
GL.Disable(EnableCap.Texture2D);
control.SwapBuffers();
That did the trick.
Very important (at least I think it is):
- the GL.Enable(EnableCap.Texture2D) just before rendering the quad with the texture and GL.Disable(EnableCap.Texture2D) afterwords.
- the GL.BindTexture(TextureTarget.Texture2D, Texture) after enabling GL.Enable(EnableCap.Texture2D).
Hope this helps someone. If I manage to have some time I'll make a C# class with it and post it here.