[fltk.opengl] texture-based text drawing and window deletion

[Manolo Gouy]

About the present texture-based Mac OS implementation
of text drawing in OpenGL windows.

There was a bug in the Mac OS 1.3 version where gl_draw() would fail
after an Fl_Gl_Window was deleted and recreated. The pre-computed
texture was re-used to draw in the new window, and this would fail.

I have implemented in r. 8536 a fix that invalidates the pile
of pre-computed textures when any Fl_Gl_Window is deleted.
This fixes the bug.

But, isn't there a better and less drastic solution ?

This short program displays the bug (before r.8536):

// run, then press 'd'
// - expected behaviour: the string is unchanged after pressing d
// - observed behaviour: the string is replaced by a rectangle

#include <FL/Fl.H>
#include <FL/Fl_Window.H>
#include <FL/Fl_Tile.H>
#include <FL/Fl_Gl_Window.H>
#include <FL/gl.h>
#if defined(__APPLE__)
#include <OpenGL/gl.h>
#include <OpenGL/glu.h>
#else
#include <GL/gl.h>
#include <GL/glu.h>
#endif

class openglWindow : public Fl_Gl_Window{
public:
  openglWindow(int x, int y, int w, int h) : Fl_Gl_Window(x, y, w, h){}
  void draw()
  {
    glClearColor(0.5, 0.3, 0.8, 0.);
    glClear(GL_DEPTH_BUFFER_BIT | GL_COLOR_BUFFER_BIT);
    glRasterPos2d(0, 0);
    gl_font(0,20);
    gl_draw("A string");
  }
};

Fl_Tile *tile;

int shortcuts(int event)
{
  if(Fl::test_shortcut('d')){
    tile->clear();

    openglWindow *gl = new openglWindow(0, 0, 400, 400);
    gl->end();
    gl->mode(FL_RGB | FL_DEPTH | FL_DOUBLE);
    tile->add(gl);
    gl->show();
  }
  return 1;
}

int main(int argc, char **argv)
{
  Fl_Window *win = new Fl_Window(0, 0, 400, 400);
  tile = new Fl_Tile(0, 0, 400, 400);
  openglWindow *gl = new openglWindow(0, 0, 400, 400);
  gl->end();
  gl->mode(FL_RGB | FL_DEPTH | FL_DOUBLE);
  tile->end();
  win->end();
  win->show(argc, argv);
  Fl::add_handler(shortcuts);
  Fl::run();
}

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