Cannot get text to be displayed

[Iconate]

I have just recently started working with OpenGL in school and am having trouble getting text to be displayed on the screen. I am not familiar with all the functions yet, this was just a blank screen code provided by my proof in which I injected my own code for the text.

#include <windows.h>
#include <math.h>
#include <stdio.h>
#include <time.h>
#include <GL/gl.h>
#include <GL/glut.g>
#include <iostream>

#define GLUT_DISABLE_ATEXIT_HACK

#define win_width 640
#define win_height 480

int font = (int)GLUT_BITMAP_8_BY_13;

using namespace std;

void renderBitmapString(float x, float y, void *font, char *string)
{
     char *c;
     glRasterPos2f(x, y);
     for (c=string; *c != '\0'; c++)
     {
         glutBitmapCharacter(font, *c);
      }
}


void init() {
	glClearColor(0.3f, 0.0f, 0.0f, 1.0f);
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	glViewport(0,0,win_width,win_height);
	gluOrtho2D(0.0f, 256.0f, 0.0f, 256.0f);
	
} // end init()


void display() {
	glClear(GL_COLOR_BUFFER_BIT);
	glutSwapBuffers();
	renderBitmapString(50,50,(void *)font,"Testing Bitmap Text");
} // end display()


int main(int argc, char* argv[]) {
  glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB);
  glutInitWindowSize(win_width, win_height);
  glutCreateWindow("Snipa");
  init();
  glutDisplayFunc(display);
  glutMainLoop();
}

The window apears, and I can change the background colour accordingly, but no text, any advice would be great, thanks.

[Iconate]

After looking into it, I think it has to do with the parameters im passing to the renderBitmapString function, but im not sure how the coordinates are created

[_Mike]

In display():
You need to render the string before you swap the buffers

[MK27]

glutSwapBuffers() is usually the second last command in a display function, right before glutPostRedisplay() when double buffering.

Here's a function I use with glut for printing text messages:

void messg2screen (int pos, char *messg, const float fg[3]) {
	int i, x, y, len = strlen(messg);
	float bg[3];

	switch (pos) {
		case (TXTBLEFT):
			x = 10;
			y = 10;
			break;
		case (TXTBRIGHT):
			x = Config.wid-12*strlen(messg)-10;
			y = 10;
			break;
		case (TXTBCENTER):
			x = Config.wid/2-12*strlen(messg)/2;
			y = 10;
			break;
		case (TXTCENTER):
			x = Config.wid/2-12*(strlen(messg)/2);
			y = Config.high/2-12;
			break;
		case (TXTTCENTER):
			x = Config.wid/2-12*(strlen(messg)/2);
			y = Config.high-20;
		default: break;
	}

	for (i=0;i<3;i++) bg[i] = 1.0f-fg[i];
	glColor4f(bg[0],bg[1],bg[1],1.0f);
	glWindowPos2i(x,y);
	for (i=0; i<len; i++) glutBitmapCharacter(GLUT_BITMAP_TIMES_ROMAN_24,messg[i]);
	glColor4f(fg[0],fg[1],fg[2],1.0f);
	glWindowPos2i(x+2,y+2);
	for (i=0; i<len; i++) glutBitmapCharacter(GLUT_BITMAP_TIMES_ROMAN_24,messg[i]);
}

This creates an inverse colored shadow so that it stands out regardless of the background. The predefined global enum for the switch/case is:

enum {
        TXTBLEFT,
        TXTBRIGHT,
        TXTBCENTER,
        TXTCENTER,
        TXTTCENTER
};

[Iconate]

After looking into it, I think it has to do with the parameters im passing to the renderBitmapString function, but im not sure how the coordinates are created

Ah perfect that worked thank you.

Also I DID manage to get it working prior, but with another example I found online...however, for the X and Y coordinate for renderBitmapCharacter, I was using decimal numbers... the whole screen could be covered from +5 to -5 rather than the actual pixel placement itself.

Why is this? The viewport was the same size as the window, but they also used a gluLookAt in their function. Is it because of this?