Member Avatar for bushimports

How can I draw text in a glut window with the keyboard;
I have tried doing cin with

void TextBox::Keys(unsigned char key,int x,int y){
   switch(key){
      case 13://enter key
      cin >> String;
       DrawString = true;
      break;    
      case 27:
        exit(0);        
      break;                    
   }

and then in the draw function

fontx = tx + 3;
          fonty = ty + (th+8)/2;
         if(DrawString == true){
         glColor3f(0.0,0.0,0.0);               
         Font(GLUT_BITMAP_HELVETICA_12,(char*)String,fontx,fonty);
}

the intention here was to get the string from cin and put it in the string variable and then draw it to the screen. I know how to get
input with cin and put it in a variable with a console program, but i don't know how to do it with the glut keyboard. I also know how to draw text to the screen with glut. I have other questions but I will post them in seperate threads. Much thanks, Jody Bush

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  • Latest Post Latest Post by mrnutty

Dani AI

Generated

, cin blocks on stdin and does not integrate with GLUT’s event loop. You want to collect characters in the keyboard callback and redraw each frame. is on the right track: register glutKeyboardFunc, append printable chars to a buffer, handle backspace/enter yourself, and call glutPostRedisplay() so your draw routine runs again. Classic GLUT only renders one character at a time (glutBitmapCharacter), while freeglut also offers helpers like glutBitmapString. (freeglut.sourceforge.net)

Here is a minimal pattern that avoids console I/O and draws in window space so your text is never clipped by your current projection/modelview:

static std::string text;

void onKey(unsigned char key, int, int) {
    switch (key) {
        case 27: std::exit(0); break;           // ESC
        case 13: /* commit/submit text */ break; // Enter
        case 8:  if (!text.empty()) text.pop_back(); break; // Backspace
        default: if (key >= 32 && key <= 126) text.push_back((char)key);
    }
    glutPostRedisplay();
}

void drawText2D(int x, int y, const std::string& s) {
    int winH = glutGet(GLUT_WINDOW_HEIGHT);
    glWindowPos2i(x, winH - y);                 // window coords, top-left origin adjustment
    for (unsigned char ch : s)
        glutBitmapCharacter(GLUT_BITMAP_HELVETICA_12, ch);
}

Notes:

  • Use glutSpecialFunc for arrows, function keys, etc., if you need editing/navigation keys. (manpages.opensuse.org)
  • glWindowPos2i sets the raster position directly in window coordinates and avoids the common gotcha where glRasterPos becomes invalid due to transforms/clipping. (docs.gl)
  • On freeglut you can tame key repeat with glutIgnoreKeyRepeat(GL_TRUE) during setup, or use glutBitmapString to render an entire C-string in one call. (freeglut.sourceforge.net)

This keeps input responsive and rendering deterministic without relying on the console.

Member Avatar for mrnutty

You could use

Combined with function you can make this :

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);
  }
}

That is provided by lighthouse, Their link

Now all you need is a little bit of logic.

For example :

string input = "";

void keyBoard(unsigned char key, int x, int y){ 
    input += key;
   void updateString();
}

and :

void updateString(){
   glutBimapString(0,0,0, GLUT_BITMAP_9_BY_15, input.c_str());
}

You can then call this function also in you draw function.

void drawFunc()
{
    glClear(someBITSGoesHerE);
    glLoadIdentity();
    updateString();
 //blah blah
}
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