Bitmap Fonts

A bitmap font is basically a 2D font. Although we’ll place it in a 3D world, these fonts will have no thickness and can’t be rotated or scaled, only translated. Furthermore, the font will always face the viewer, like a billboard. Although this can be seen as a potential disadvantage, on the other hand we won’t have to worry about orienting the font to face the viewer

In this section we’ll present the GLUT functions to put some bitmapped text on the screen. We’re going to need one function to write a char: glutBitmapCharacter. The syntax is as follows:

void glutBitmapCharacter(void *font, int character)

Parameters:

• font – the name of the font to use (see bellow for a list of what’s available
• character – what to render, a letter, symbol, number, etc…

The font options available are:

• GLUT_BITMAP_8_BY_13
• GLUT_BITMAP_9_BY_15
• GLUT_BITMAP_TIMES_ROMAN_10
• GLUT_BITMAP_TIMES_ROMAN_24
• GLUT_BITMAP_HELVETICA_10
• GLUT_BITMAP_HELVETICA_12
• GLUT_BITMAP_HELVETICA_18

Some of the font names are recognizable so you’ll probably know what to expect, nevertheless you’ll have the opportunity of trying all fonts in the example application via a pop-up menu.

The following line of text exemplifies a call to the glutBitmapCharacter function to output a single character at the current raster position:

glutBitmapCharacter(GLUT_BITMAP_HELVETICA_18,'3');

One important thing to know is what is the actual raster position. The raster position can be set with the family of functions glRasterPos from the OpenGL library. The syntax of two functions from this family is presented below.

void glRasterPos2f(float x, float y);
void glRasterPos3f(float x, float y, float z);

Parameters:

• x, y, z – local coordinates for the text to appear

The function glutBitmapCharacter renders the character at the required position and advances the current raster position by the width of the character. Therefore, to render a string, successive calls to glutBitmapCharacter will suffice to achieve the desired output. The following function renders a string starting at the specified raster position:

void renderBitmapString(
		float x,
		float y,
		float z,
		void *font,
		char *string) {

  char *c;
  glRasterPos3f(x, y,z);
  for (c=string; *c != '\0'; c++) {
    glutBitmapCharacter(font, *c);
  }
}