Best way to display diagnostic text in Windows OpenGL

Question

I have an artsy opengl app that I am working on. The final product will have no need to display text. But during developement I want to display odd bits of data for diagnostic purposes, like framerate, object count. I would like the rendering of the text not to dramatically decrease the performance of the code.

I realize this is a mildly subjective question, but all the same I would appreciate your thoughts

Answer 1

I wrote an opengl text renderer using just the gl_line primitives if that suits your needs:

#ifndef SIMPLETEXT_H
#define SIMPLETEXT_H

#include <GL/gl.h>

namespace SimpleText  {

   // internal vertex
   union vertex  {
      float data[3];
   };

   // use 15 verts to hold all possible letters
   // 0 - 1 - 2
   // 3 - 4 - 5
   // 6 - 7 - 8
   // 9 - 10- 11
   // 12- 13- 14
   vertex verts[15] = {
      {0, 4, 0}, {1, 4, 0}, {2, 4, 0},
      {0, 3, 0}, {1, 3, 0}, {2, 3, 0},
      {0, 2, 0}, {1, 2, 0}, {2, 2, 0},
      {0, 1, 0}, {1, 1, 0}, {2, 1, 0},
      {0, 0, 0}, {1, 0, 0}, {2, 0, 0}
   };

   // start/end char values
   const int START = 33;
   const int END = 90;

   // size of the window (assumed square)
   // increase this to decrease the size of text
   const int WINDOW_EXTENT = 300;

   // use index arrays to create letters
   unsigned int letters[END - START + 1][15] = {
      {4, 1, 7, 13, 14, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},      // !
      {4, 1, 4, 2, 5, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},        // "
      {8, 0, 12, 2, 14, 3, 5, 9, 11, 0, 0, 0, 0, 0, 0},     // #
      {8, 2, 3, 3, 11, 11, 12, 1, 13, 0, 0, 0, 0, 0, 0},    // $
      {14, 2, 12, 0, 3, 3, 1, 1, 0, 11, 13, 13, 14, 14, 11}, // %
      {14, 14, 3, 3, 1, 1, 7, 7, 9, 9, 12, 12, 13, 13, 11}, // &
      {2, 1, 4, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},        // '
      {6, 1, 3, 3, 9, 9, 13, 0, 0, 0, 0, 0, 0, 0, 0},       // (
      {6, 1, 5, 5, 11, 11, 13, 0, 0, 0, 0, 0, 0, 0, 0},     // )
      {6, 0, 8, 6, 2, 1, 7, 0, 0, 0, 0, 0, 0, 0, 0},        // *
      {4, 6, 8, 4, 10, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},       // +
      {2, 10, 12, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},      // ,
      {2, 6, 8, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},        // -
      {8, 12, 13, 13, 10, 10, 9, 9, 12, 0, 0, 0, 0, 0, 0},  // .
      {2, 2, 12, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},       // /
      {10, 0, 2, 2, 14, 14, 12, 12, 0, 0, 14, 0, 0, 0, 0},  // 0
      {6, 3, 1, 1, 13, 12, 14, 0, 0, 0, 0, 0, 0, 0, 0},     // 1
      {10, 3, 1, 1, 5, 5, 8, 8, 12, 12, 14, 0, 0, 0, 0},    // 2
      {12, 0, 1, 1, 5, 5, 11, 11, 13, 13, 12, 8, 7, 0, 0},  // 3
      {6, 14, 2, 2, 6, 6, 8, 0, 0, 0, 0, 0, 0, 0, 0},       // 4
      {12, 2, 0, 0, 6, 6, 7, 7, 11, 11, 13, 13, 12, 0, 0},  // 5
      {14, 2, 1, 1, 3, 3, 12, 12, 13, 13, 11, 11, 7, 7, 6}, // 6
      {4, 0, 2, 2, 12, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},       // 7
      {12, 1, 3, 3, 11, 11, 13, 13, 9, 9, 5, 5, 1, 0, 0},   // 8
      {10, 2, 1, 1, 3, 3, 7, 7, 8, 2, 14, 0, 0, 0, 0},      // 9
      {4, 1, 4, 10, 13, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},      // :
      {4, 1, 4, 10, 12, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},      // ;
      {4, 5, 6, 6, 11, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},       // <
      {4, 5, 3, 9, 11, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},       // =
      {4, 3, 8, 8, 9, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},        // >
      {8, 3, 1, 1, 5, 5, 7, 7, 10, 0, 0, 0, 0, 0, 0},       // ?
      {14, 4, 7, 7, 8, 8, 5, 5, 1, 1, 3, 3, 9, 9, 14},      // @
      {10, 1, 6, 1, 8, 6, 12, 8, 14, 6, 8, 0, 0, 0, 0},     // A
      {14, 0, 12, 0, 5, 5, 7, 7, 6, 7, 11, 11, 13, 13, 12}, // B
      {10, 2, 1, 1, 3, 3, 9, 9, 13, 13, 14, 0, 0, 0, 0},    // C
      {12, 0, 1, 1, 5, 5, 11, 11, 13, 13, 12, 12, 0, 0, 0}, // D
      {8, 0, 12, 0, 2, 6, 7, 12, 14, 0, 0, 0, 0, 0, 0},     // E
      {6, 0, 12, 0, 2, 6, 7, 0, 0, 0, 0, 0, 0, 0, 0},       // F
      {14, 2, 1, 1, 3, 3, 9, 9, 13, 13, 11, 11, 8, 8, 7},   // G
      {6, 0, 12, 6, 8, 2, 14, 0, 0, 0, 0, 0, 0, 0, 0},      // H
      {6, 0, 2, 1, 13, 12, 14, 0, 0, 0, 0, 0, 0, 0, 0},     // I
      {8, 1, 2, 2, 11, 11, 13, 13, 9, 0, 0, 0, 0, 0, 0},    // J
      {6, 0, 12, 6, 2, 6, 14, 0, 0, 0, 0, 0, 0, 0, 0},      // K
      {4, 0, 12, 12, 14, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},     // L
      {8, 0, 12, 0, 7, 7, 2, 2, 14, 0, 0, 0, 0, 0, 0},      // M
      {6, 0, 12, 0, 14, 14, 2, 0, 0, 0, 0, 0, 0, 0, 0},     // N
      {12, 1, 5, 5, 11, 11, 13, 13, 9, 9, 3, 3, 1, 0, 0},   // O
      {10, 0, 12, 0, 1, 1, 5, 5, 7, 7, 6, 0, 0, 0, 0},      // P
      {12, 0, 12, 12, 13, 13, 11, 11, 2, 2, 0, 10, 14, 0, 0},  // Q
      {12, 0, 12, 0, 1, 1, 5, 5, 7, 7, 6, 7, 14, 0, 0},     // R
      {14, 2, 1, 1, 3, 3, 6, 6, 8, 8, 11, 11, 13, 13, 12},  // S
      {4, 0, 2, 1, 13, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},       // T
      {8, 0, 9, 9, 13, 13, 11, 11, 2, 0, 0, 0, 0, 0, 0},    // U
      {4, 0, 13, 13, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},      // V
      {8, 0, 12, 12, 1, 1, 14, 14, 2, 0, 0, 0, 0, 0, 0},    // W
      {4, 0, 14, 2, 12, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},      // X
      {6, 0, 7, 7, 2, 7, 13, 0, 0, 0, 0, 0, 0, 0, 0},       // Y
      {6, 0, 2, 2, 12, 12, 14, 0, 0, 0, 0, 0, 0, 0, 0}      // Z
   };

}

// Draws a string of length <len> at an <x>/<y> position on the screen, optionally with a <shadow>
//  The screen is set up to be 0,0 at the lower left and 150,150 at the upper right for positioning
//  by default.
static void DrawText(const char * string, int len, float x, float y, bool shadow = false)  {
   if (len <= 0) return;

   glPushMatrix();
   glLoadIdentity();

   glMatrixMode(GL_PROJECTION);
   glPushMatrix();

   glLoadIdentity();
   glOrtho(0, SimpleText::WINDOW_EXTENT, 0, SimpleText::WINDOW_EXTENT, -10, 10);

   glMatrixMode(GL_MODELVIEW);

   glBindTexture(GL_TEXTURE_2D, 0);

   glVertexPointer(3, GL_FLOAT, 0, SimpleText::verts);
   glEnableClientState(GL_VERTEX_ARRAY);

   char temp = 0;

   // draw first copy if we need a shadow
   if (shadow)  {
      glTranslatef(x + 0.3, y - 0.5, 0);
      glColor4f(0.0f, 0.0f, 0.0f, 1.0f);

      for (int i = 0; i < len; i++)  {
         temp = string[i];
         temp = (temp < 97) ? temp : temp - 32;
         if (temp >= SimpleText::START && temp <= SimpleText::END)  {

            glDrawElements(
               GL_LINES, 
               SimpleText::letters[temp - SimpleText::START][0], 
               GL_UNSIGNED_INT, 
               &(SimpleText::letters[temp - SimpleText::START][1])
            );
         }

         glTranslatef(2.7f, 0, 0);
      }
   }

   glLoadIdentity();
   glTranslatef(x, y, 0);
   glColor4f(1.0f, 1.0f, 1.0f, 1.0f);

   // draw regular text
   for (int i = 0; i < len; i++)  {
      temp = string[i];
      temp = (temp < 97) ? temp : temp - 32;
      if (temp >= SimpleText::START && temp <= SimpleText::END)  {

         glDrawElements(
            GL_LINES, 
            SimpleText::letters[temp - SimpleText::START][0], 
            GL_UNSIGNED_INT, 
            &(SimpleText::letters[temp - SimpleText::START][1])
         );
      }

      glTranslatef(2.7f, 0, 0);
   }

   glDisableClientState(GL_VERTEX_ARRAY);


   glMatrixMode(GL_PROJECTION);
   glPopMatrix();

   glMatrixMode(GL_MODELVIEW);
   glPopMatrix();
}

#endif