JMU
Text in OpenGL
An Introduction


Prof. David Bernstein
James Madison University

Computer Science Department
bernstdh@jmu.edu


Getting Started
GLUT Bitmap Fonts
GLUT Bitmap Fonts (cont.)

An Example

openglexamples/text/bitmapfontGLUT.c (Fragment: drawString) 
        /**
 * Draw a character string.
 *
 * @param x        The x position
 * @param y        The y position
 * @param z        The z position
 * @param string   The character string
 */
void drawString(float x, float y, float z, char *string) {
  glRasterPos3f(x, y, z);

  for (char* c = string; *c != '\0'; c++) {
    glutBitmapCharacter(currentFont, *c);  // Updates the position
  }
}
Working in Screen Coordinates
Working in Screen Coordinates (cont.)

Handling Reshape Events

openglexamples/text/labelsGLUT.c (Fragment: reshape) 
        /**
 * The reshape callback.
 *
 * @param w   The width
 * @param h   The height
 */
void reshape(int w, int h) {
  GLfloat aspect;

  // Save the width and height for text processing
  width = w;
  height = h;

  glViewport(0, 0, (GLsizei) w, (GLsizei) h);

  glMatrixMode(GL_PROJECTION);

  glLoadIdentity();

  if (w <= h) {
    aspect = (GLfloat) h / (GLfloat) w;
    glOrtho(-1.5, 1.5, -1.5 * aspect, 1.5 * aspect, -10.0, 10.0);
  } else {
    aspect = (GLfloat) w / (GLfloat) h;
    glOrtho(-1.5 * aspect, 1.5 * aspect, -1.5, 1.5, -10.0, 10.0);
  }
}

/**
 * The entry point of the application.
 *
 * This function contains calls to GLUT.
 *
 * @param argc  The number of command line arguments
 * @param argv  The array of command line arguments
 * @return      A status code
 */
int main(int argc, char** argv) {
  glutInit(&argc, argv);

  window = createWindow("Bitmap Fonts", 640, 480, 0, 0);

  glutDisplayFunc(display);
  glutReshapeFunc(reshape);

  init();

  glutMainLoop();
}
Working in Screen Coordinates (cont.)

The Overall Process

openglexamples/text/labelsGLUT.c (Fragment: paint) 
        /**
 * Display/render the OpenGL window.
 */
void display() {
  glClear(GL_COLOR_BUFFER_BIT);
  glColor3f(0.0, 0.0, 0.0);

  // Set things up so that we can render text in
  // window coordinates
  beginText();

  // Render the text
  drawString(0.0, 0.0, "James Madison University");

  // Set things up for normal rendering
  endText();

  // Normal rendering of the scene goes here

  glFlush();
}
Working in Screen Coordinates (cont.)

Before Rendering Text

openglexamples/text/labelsGLUT.c (Fragment: beginText) 
        /**
 * Setup the state for text.
 */
void beginText() {
  glMatrixMode(GL_PROJECTION);

  // Save the current projection matrix
  glPushMatrix();

  // Make the current matrix the identity matrix
  glLoadIdentity();

  // Set the projection (to 2D orthographic)
  gluOrtho2D(0, width, 0, height);

  glMatrixMode(GL_MODELVIEW);
}
Working in Screen Coordinates (cont.)

After Rendering Text

openglexamples/text/labelsGLUT.c (Fragment: endText) 
        /**
 * End the state for text.
 */
void endText() {
  glMatrixMode(GL_PROJECTION);

  // Restore the original projection matrix
  glPopMatrix();

  glMatrixMode(GL_MODELVIEW);
}
GLUT Vector/Stroke Fonts
GLUT Vector/Stroke Fonts (cont.)

An Example

openglexamples/text/vectorfontGLUT.c (Fragment: drawString) 
        /**
 * Draw a character string.
 *
 * @param x        The x position
 * @param y        The y position
 * @param z        The z position
 * @param string   The character string
 */
void drawString(float x, float y, float z, char *string) {
  // Save the current matrix
  glPushMatrix();

  // Translate to the appropriate starting point
  glTranslatef(x, y, z);

  // Note: We could change the line width with glLineWidth()

  // Render the characters
  for (char* c = string; *c != '\0'; c++) {
    glutStrokeCharacter(currentFont, *c);
  }

  // Another useful function
  //    int glutStrokeWidth(void *font, int character);

  // Retrieve the original matrix
  glPopMatrix();
}
Working in OpenGL
Working in OpenGL (cont.)

An Example from the "Red Book"

openglexamples/text/font.c 
        /**
 * Copyright (c) 1993-1997, Silicon Graphics, Inc.
 * ALL RIGHTS RESERVED 
 * Permission to use, copy, modify, and distribute this software for 
 * any purpose and without fee is hereby granted, provided that the above
 * copyright notice appear in all copies and that both the copyright notice
 * and this permission notice appear in supporting documentation, and that 
 * the name of Silicon Graphics, Inc. not be used in advertising
 * or publicity pertaining to distribution of the software without specific,
 * written prior permission. 
 *
 * THE MATERIAL EMBODIED ON THIS SOFTWARE IS PROVIDED TO YOU "AS-IS"
 * AND WITHOUT WARRANTY OF ANY KIND, EXPRESS, IMPLIED OR OTHERWISE,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTY OF MERCHANTABILITY OR
 * FITNESS FOR A PARTICULAR PURPOSE.  IN NO EVENT SHALL SILICON
 * GRAPHICS, INC.  BE LIABLE TO YOU OR ANYONE ELSE FOR ANY DIRECT,
 * SPECIAL, INCIDENTAL, INDIRECT OR CONSEQUENTIAL DAMAGES OF ANY
 * KIND, OR ANY DAMAGES WHATSOEVER, INCLUDING WITHOUT LIMITATION,
 * LOSS OF PROFIT, LOSS OF USE, SAVINGS OR REVENUE, OR THE CLAIMS OF
 * THIRD PARTIES, WHETHER OR NOT SILICON GRAPHICS, INC.  HAS BEEN
 * ADVISED OF THE POSSIBILITY OF SUCH LOSS, HOWEVER CAUSED AND ON
 * ANY THEORY OF LIABILITY, ARISING OUT OF OR IN CONNECTION WITH THE
 * POSSESSION, USE OR PERFORMANCE OF THIS SOFTWARE.
 * 
 * US Government Users Restricted Rights 
 * Use, duplication, or disclosure by the Government is subject to
 * restrictions set forth in FAR 52.227.19(c)(2) or subparagraph
 * (c)(1)(ii) of the Rights in Technical Data and Computer Software
 * clause at DFARS 252.227-7013 and/or in similar or successor
 * clauses in the FAR or the DOD or NASA FAR Supplement.
 * Unpublished-- rights reserved under the copyright laws of the
 * United States.  Contractor/manufacturer is Silicon Graphics,
 * Inc., 2011 N.  Shoreline Blvd., Mountain View, CA 94039-7311.
 *
 * OpenGL(R) is a registered trademark of Silicon Graphics, Inc.
 */

#include <stdlib.h>
#include <string.h>
#include <GL/glut.h>


GLubyte space[] = 
{0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};

GLubyte letters[][13] = {
{0x00, 0x00, 0xc3, 0xc3, 0xc3, 0xc3, 0xff, 0xc3, 0xc3, 0xc3, 0x66, 0x3c, 0x18}, 
{0x00, 0x00, 0xfe, 0xc7, 0xc3, 0xc3, 0xc7, 0xfe, 0xc7, 0xc3, 0xc3, 0xc7, 0xfe}, 
{0x00, 0x00, 0x7e, 0xe7, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0, 0xe7, 0x7e}, 
{0x00, 0x00, 0xfc, 0xce, 0xc7, 0xc3, 0xc3, 0xc3, 0xc3, 0xc3, 0xc7, 0xce, 0xfc}, 
{0x00, 0x00, 0xff, 0xc0, 0xc0, 0xc0, 0xc0, 0xfc, 0xc0, 0xc0, 0xc0, 0xc0, 0xff}, 
{0x00, 0x00, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0, 0xfc, 0xc0, 0xc0, 0xc0, 0xff}, 
{0x00, 0x00, 0x7e, 0xe7, 0xc3, 0xc3, 0xcf, 0xc0, 0xc0, 0xc0, 0xc0, 0xe7, 0x7e}, 
{0x00, 0x00, 0xc3, 0xc3, 0xc3, 0xc3, 0xc3, 0xff, 0xc3, 0xc3, 0xc3, 0xc3, 0xc3}, 
{0x00, 0x00, 0x7e, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x7e}, 
{0x00, 0x00, 0x7c, 0xee, 0xc6, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06}, 
{0x00, 0x00, 0xc3, 0xc6, 0xcc, 0xd8, 0xf0, 0xe0, 0xf0, 0xd8, 0xcc, 0xc6, 0xc3}, 
{0x00, 0x00, 0xff, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0}, 
{0x00, 0x00, 0xc3, 0xc3, 0xc3, 0xc3, 0xc3, 0xc3, 0xdb, 0xff, 0xff, 0xe7, 0xc3}, 
{0x00, 0x00, 0xc7, 0xc7, 0xcf, 0xcf, 0xdf, 0xdb, 0xfb, 0xf3, 0xf3, 0xe3, 0xe3}, 
{0x00, 0x00, 0x7e, 0xe7, 0xc3, 0xc3, 0xc3, 0xc3, 0xc3, 0xc3, 0xc3, 0xe7, 0x7e}, 
{0x00, 0x00, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0, 0xfe, 0xc7, 0xc3, 0xc3, 0xc7, 0xfe}, 
{0x00, 0x00, 0x3f, 0x6e, 0xdf, 0xdb, 0xc3, 0xc3, 0xc3, 0xc3, 0xc3, 0x66, 0x3c}, 
{0x00, 0x00, 0xc3, 0xc6, 0xcc, 0xd8, 0xf0, 0xfe, 0xc7, 0xc3, 0xc3, 0xc7, 0xfe}, 
{0x00, 0x00, 0x7e, 0xe7, 0x03, 0x03, 0x07, 0x7e, 0xe0, 0xc0, 0xc0, 0xe7, 0x7e}, 
{0x00, 0x00, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0xff}, 
{0x00, 0x00, 0x7e, 0xe7, 0xc3, 0xc3, 0xc3, 0xc3, 0xc3, 0xc3, 0xc3, 0xc3, 0xc3}, 
{0x00, 0x00, 0x18, 0x3c, 0x3c, 0x66, 0x66, 0xc3, 0xc3, 0xc3, 0xc3, 0xc3, 0xc3}, 
{0x00, 0x00, 0xc3, 0xe7, 0xff, 0xff, 0xdb, 0xdb, 0xc3, 0xc3, 0xc3, 0xc3, 0xc3}, 
{0x00, 0x00, 0xc3, 0x66, 0x66, 0x3c, 0x3c, 0x18, 0x3c, 0x3c, 0x66, 0x66, 0xc3}, 
{0x00, 0x00, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x3c, 0x3c, 0x66, 0x66, 0xc3}, 
{0x00, 0x00, 0xff, 0xc0, 0xc0, 0x60, 0x30, 0x7e, 0x0c, 0x06, 0x03, 0x03, 0xff}
};

GLuint fontOffset;

void makeRasterFont(void)
{
   GLuint i, j;
   glPixelStorei(GL_UNPACK_ALIGNMENT, 1);

   fontOffset = glGenLists (128);
   for (i = 0,j = 'A'; i < 26; i++,j++) {
      glNewList(fontOffset + j, GL_COMPILE);
      glBitmap(8, 13, 0.0, 2.0, 10.0, 0.0, letters[i]);
      glEndList();
   }
   glNewList(fontOffset + ' ', GL_COMPILE);
   glBitmap(8, 13, 0.0, 2.0, 10.0, 0.0, space);
   glEndList();
}

void init(void)
{
   glShadeModel (GL_FLAT);
   makeRasterFont();
}

void printString(char *s)
{
   glPushAttrib (GL_LIST_BIT);
   glListBase(fontOffset);
   glCallLists((GLsizei) strlen(s), GL_UNSIGNED_BYTE, (GLubyte *) s);
   glPopAttrib ();
}

/* Everything above this line could be in a library 
 * that defines a font.  To make it work, you've got 
 * to call makeRasterFont() before you start making 
 * calls to printString().
 */
void display(void)
{
   GLfloat white[3] = { 1.0, 1.0, 1.0 };

   glClear(GL_COLOR_BUFFER_BIT);
   glColor3fv(white);

   glRasterPos2i(20, 60);
   printString("THE QUICK BROWN FOX JUMPS");
   glRasterPos2i(20, 40);
   printString("OVER A LAZY DOG");
   glFlush ();
}

void reshape(int w, int h)
{
   glViewport(0, 0, (GLsizei) w, (GLsizei) h);
   glMatrixMode(GL_PROJECTION);
   glLoadIdentity();
   glOrtho (0.0, w, 0.0, h, -1.0, 1.0);
   glMatrixMode(GL_MODELVIEW);
}

/* ARGSUSED1 */
void keyboard(unsigned char key, int x, int y)
{
   switch (key) {
      case 27:
         exit(0);
   }
}

/*  Main Loop
 *  Open window with initial window size, title bar, 
 *  RGBA display mode, and handle input events.
 */
int main(int argc, char** argv)
{
   glutInit(&argc, argv);
   glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
   glutInitWindowSize(300, 100);
   glutInitWindowPosition (100, 100);
   glutCreateWindow(argv[0]);
   init();
   glutReshapeFunc(reshape);
   glutKeyboardFunc(keyboard);
   glutDisplayFunc(display);
   glutMainLoop();
   return 0;
}