How to Use GLUT Bitmap Fonts in Your OpenGL Application

When developing graphics applications using OpenGL, text rendering can become a challenge, especially if you want to avoid implementing your own font rendering system. Luckily, GLUT provides a simple solution through bitmap fonts that can be used within your application. This blog post will guide you on how to implement and display texture with GLUT bitmap fonts easily.

What Are GLUT Bitmap Fonts?

GLUT bitmap fonts are basic 2D fonts that come with the GLUT toolkit. They are not designed for use in a three-dimensional environment, but they work perfectly for overlaying text in your OpenGL display window.

Preparing Your OpenGL Application

To display text using GLUT bitmap fonts, you need to set up your OpenGL context appropriately. Here’s how you can do this step-by-step:

Step 1: Setting Up the Projection and Modelview Matrices

First, you need to enable 2D rendering by configuring the projection and modelview matrices. The following code accomplishes that:

glMatrixMode(GL_PROJECTION);
glPushMatrix();
glLoadIdentity();
gluOrtho2D(0.0, WIN_WIDTH, 0.0, WIN_HEIGHT); // Set 2D orthographic projection

glMatrixMode(GL_MODELVIEW);
glPushMatrix();
glLoadIdentity(); // Reset the modelview matrix

Step 2: Define Your Font Color

Choosing a color for your text is essential. Set this color at the beginning of your rendering code to ensure it applies correctly.

glColor3f(0.0, 1.0, 0.0); // Set color to green

Step 3: Set the Raster Position

Specify where you want the text to appear in your window. The lower-left corner of your display is denoted as the coordinates (0, 0). Here’s how you set it:

glRasterPos2i(10, 10); // Position the text at (10, 10)

Step 4: Displaying the Text

To display your desired string, you’ll need to utilize the glutBitmapCharacter function, which takes the font style and each character of your string. Below is an example of how to display a quote:

string s = "Respect mah authoritah!";
void * font = GLUT_BITMAP_9_BY_15; // Select the font here

for (string::iterator i = s.begin(); i != s.end(); ++i) {
    char c = *i;
    glutBitmapCharacter(font, c); // Render each character
}

Step 5: Restore the Matrices

Finally, it’s important to restore the OpenGL state back to what it was before you made the changes for rendering text:

glMatrixMode(GL_MODELVIEW);
glPopMatrix();

glMatrixMode(GL_PROJECTION);
glPopMatrix();

Conclusion

Using GLUT bitmap fonts allows for simple text rendering in your OpenGL applications, enhancing user experience through clear communication without needing to dive into more complex font rendering solutions. By following the steps outlined above, you can integrate text into your application comfortably.

So why wait? Start implementing GLUT bitmap fonts in your OpenGL application today, and make your graphics even more engaging!