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Add cross-platform support for adding widgets to an OpenGL3-based Fl_Gl_Window.

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Under non-macOS platforms, the key is to call glUseProgram(0); after having used OpenGL 3
which allows to then use OpenGL 1 and draw FLTK widgets over the OpenGL3 scene.

Under macOS, this is impossible because macOS GL3 contexts are not compatible
with GL1. The solution implemented here is to create an additional Fl_Gl_Window
placed above and sized as the GL3-based window, to give it a non opaque,
GL1-based context, and to put the FLTK widgets in that additional window.
This commit is contained in:
ManoloFLTK
2022-09-25 16:39:40 +02:00
parent 0fd10e9fde
commit 89f9671b40
5 changed files with 130 additions and 1 deletions
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32
examples/OpenGL3test.cxx
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@@ -138,6 +138,13 @@ public:
GLfloat p[]={0,0};
glUniform2fv(positionUniform, 1, (const GLfloat *)&p);
glDrawArrays(GL_TRIANGLE_FAN, 0, 4);
#ifndef __APPLE__
// suggested by https://stackoverflow.com/questions/22293870/mixing-fixed-function-pipeline-and-programmable-pipeline-in-opengl
// Switch from GL3-style to GL1-style drawing;
// good under Windows, X11 and Wayland; impossible under macOS.
glUseProgram(0);
Fl_Gl_Window::draw(); // Draw FLTK child widgets.
#endif
}
virtual int handle(int event) {
static int first = 1;
@@ -161,6 +168,9 @@ public:
redraw();
}
int retval = Fl_Gl_Window::handle(event);
if (retval) return retval;
if (event == FL_PUSH && gl_version_major >= 3) {
static float factor = 1.1;
GLfloat data[4];
@@ -175,7 +185,7 @@ public:
add_output("push Fl_Gl_Window::pixels_per_unit()=%.1f\n", pixels_per_unit());
return 1;
}
return Fl_Gl_Window::handle(event);
return retval;
}
void reset(void) { shaderProgram = 0; }
};
@@ -218,6 +228,25 @@ void add_output(const char *format, ...)
}
void button_cb(Fl_Widget *, void *) {
add_output("run button callback\n");
}
void add_widgets(Fl_Gl_Window *g) {
#ifdef __APPLE__
g = fl_mac_prepare_add_widgets_to_GL3_win(g);
#endif
Fl::set_color(FL_FREE_COLOR, 255, 0, 0, 140); // partially transparent red
g->begin();
// Create here widgets to go above the GL3 scene
Fl_Button* b = new Fl_Button( 0, 170, 60, 30, "button");
b->color(FL_FREE_COLOR);
b->box(FL_BORDER_BOX );
b->callback(button_cb, NULL);
g->end();
}
int main(int argc, char **argv)
{
Fl::use_high_res_GL(1);
@@ -225,6 +254,7 @@ int main(int argc, char **argv)
SimpleGL3Window *win = new SimpleGL3Window(0, 0, 300, 300);
win->end();
output_win(win);
add_widgets(win);
topwin->end();
topwin->resizable(win);
topwin->label("Click GL panel to reshape");