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fltk/examples/OpenGL3test.cxx

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//
// Tiny OpenGL v3 demo program for the Fast Light Tool Kit (FLTK).
//
// Copyright 1998-2024 by Bill Spitzak and others.
//
// This library is free software. Distribution and use rights are outlined in
// the file "COPYING" which should have been included with this file. If this
// file is missing or damaged, see the license at:
//
// https://www.fltk.org/COPYING.php
//
// Please see the following page on how to report bugs and issues:
//
// https://www.fltk.org/bugs.php
//
#include <stdarg.h>
#include <FL/Fl.H>
#include <FL/platform.H>
#include <FL/Fl_Window.H>
#include <FL/Fl_Gl_Window.H>
#include <FL/Fl_Light_Button.H>
#include <FL/Fl_Text_Display.H>
#include <FL/Fl_Text_Buffer.H>
#if defined(__APPLE__)
# include <OpenGL/gl3.h> // defines OpenGL 3.0+ functions
#else
// Note: GLEW_STATIC is defined by CMake if the static lib is linked
# include <GL/glew.h>
#endif
#include <FL/gl.h> // for gl_texture_reset()
void add_output(const char *format, ...);
class SimpleGL3Window : public Fl_Gl_Window {
GLuint shaderProgram;
GLuint vertexArrayObject;
GLuint vertexBuffer;
GLint positionUniform;
GLint colourAttribute;
GLint positionAttribute;
int gl_version_major;
public:
SimpleGL3Window(int x, int y, int w, int h) : Fl_Gl_Window(x, y, w, h) {
mode(FL_RGB8 | FL_DOUBLE | FL_OPENGL3);
shaderProgram = 0;
gl_version_major = 0;
}
void draw(void) FL_OVERRIDE {
if (gl_version_major >= 3 && !shaderProgram) {
GLuint vs;
GLuint fs;
int Mslv, mslv; // major and minor version numbers of the shading language
sscanf((char*)glGetString(GL_SHADING_LANGUAGE_VERSION), "%d.%d", &Mslv, &mslv);
add_output("Shading Language Version=%d.%d\n",Mslv, mslv);
const char *vss_format="#version %d%d\n\
uniform vec2 p;\
in vec4 position;\
in vec4 colour;\
out vec4 colourV;\
void main (void)\
{\
colourV = colour;\
gl_Position = vec4(p, 0.0, 0.0) + position;\
}";
char vss_string[300]; const char *vss = vss_string;
snprintf(vss_string, 300, vss_format, Mslv, mslv);
const char *fss_format="#version %d%d\n\
in vec4 colourV;\
out vec4 fragColour;\
void main(void)\
{\
fragColour = colourV;\
}";
char fss_string[200]; const char *fss = fss_string;
snprintf(fss_string, 200, fss_format, Mslv, mslv);
GLint err; GLchar CLOG[1000]; GLsizei length;
vs = glCreateShader(GL_VERTEX_SHADER);
glShaderSource(vs, 1, &vss, NULL);
glCompileShader(vs);
glGetShaderiv(vs, GL_COMPILE_STATUS, &err);
if (err != GL_TRUE) {
glGetShaderInfoLog(vs, sizeof(CLOG), &length, CLOG);
add_output("vs ShaderInfoLog=%s\n",CLOG);
}
fs = glCreateShader(GL_FRAGMENT_SHADER);
glShaderSource(fs, 1, &fss, NULL);
glCompileShader(fs);
glGetShaderiv(fs, GL_COMPILE_STATUS, &err);
if (err != GL_TRUE) {
glGetShaderInfoLog(fs, sizeof(CLOG), &length, CLOG);
add_output("fs ShaderInfoLog=%s\n",CLOG);
}
// Attach the shaders
shaderProgram = glCreateProgram();
glAttachShader(shaderProgram, vs);
glAttachShader(shaderProgram, fs);
glBindFragDataLocation(shaderProgram, 0, "fragColour");
glLinkProgram(shaderProgram);
glGetProgramiv(shaderProgram, GL_LINK_STATUS, &err);
if (err != GL_TRUE) {
glGetProgramInfoLog(shaderProgram, sizeof(CLOG), &length, CLOG);
add_output("link log=%s\n", CLOG);
}
// Get pointers to uniforms and attributes
positionUniform = glGetUniformLocation(shaderProgram, "p");
colourAttribute = glGetAttribLocation(shaderProgram, "colour");
positionAttribute = glGetAttribLocation(shaderProgram, "position");
glDeleteShader(vs);
glDeleteShader(fs);
// Upload vertices (1st four values in a row) and colours (following four values)
GLfloat vertexData[]= { -0.5,-0.5,0.0,1.0, 1.0,0.0,0.0,1.0,
-0.5, 0.5,0.0,1.0, 0.0,1.0,0.0,1.0,
0.5, 0.5,0.0,1.0, 0.0,0.0,1.0,1.0,
0.5,-0.5,0.0,1.0, 1.0,1.0,1.0,1.0};
glGenVertexArrays(1, &vertexArrayObject);
glBindVertexArray(vertexArrayObject);
glGenBuffers(1, &vertexBuffer);
glBindBuffer(GL_ARRAY_BUFFER, vertexBuffer);
glBufferData(GL_ARRAY_BUFFER, 4*8*sizeof(GLfloat), vertexData, GL_STATIC_DRAW);
glEnableVertexAttribArray((GLuint)positionAttribute);
glEnableVertexAttribArray((GLuint)colourAttribute );
glVertexAttribPointer((GLuint)positionAttribute, 4, GL_FLOAT, GL_FALSE, 8*sizeof(GLfloat), 0);
glVertexAttribPointer((GLuint)colourAttribute , 4, GL_FLOAT, GL_FALSE, 8*sizeof(GLfloat), (char*)0+4*sizeof(GLfloat));
glUseProgram(shaderProgram);
}
else if ((!valid())) {
glViewport(0, 0, pixel_w(), pixel_h());
}
glClearColor(0.08f, 0.8f, 0.8f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);
if (shaderProgram) {
GLfloat p[]={0,0};
glUniform2fv(positionUniform, 1, (const GLfloat *)&p);
glDrawArrays(GL_TRIANGLE_FAN, 0, 4);
}
Fl_Gl_Window::draw(); // Draw FLTK child widgets.
}
int handle(int event) FL_OVERRIDE {
static int first = 1;
if (first && event == FL_SHOW && shown()) {
first = 0;
make_current();
#ifndef __APPLE__
GLenum err = glewInit(); // defines pters to functions of OpenGL V 1.2 and above
# ifdef FLTK_USE_WAYLAND
// glewInit returns GLEW_ERROR_NO_GLX_DISPLAY with Wayland
// see https://github.com/nigels-com/glew/issues/273
if (fl_wl_display() && err == GLEW_ERROR_NO_GLX_DISPLAY) err = GLEW_OK;
# endif
if (err) Fl::warning("glewInit() failed returning %u", err);
else add_output("Using GLEW %s\n", glewGetString(GLEW_VERSION));
#endif
const uchar *glv = glGetString(GL_VERSION);
add_output("GL_VERSION=%s\n", glv);
sscanf((const char *)glv, "%d", &gl_version_major);
if (gl_version_major < 3) {
add_output("\nThis platform does not support OpenGL V3 :\n"
"FLTK widgets will appear but the programmed "
"rendering pipeline will not run.\n");
mode(mode() & ~FL_OPENGL3);
}
redraw();
}
int retval = Fl_Gl_Window::handle(event);
if (retval) return retval;
if (event == FL_PUSH && gl_version_major >= 3) {
static float factor = 1.1f;
GLfloat data[4];
glGetBufferSubData(GL_ARRAY_BUFFER, 0, 4*sizeof(GLfloat), data);
if (data[0] < -0.88 || data[0] > -0.5) factor = 1/factor;
data[0] *= factor;
glBufferSubData(GL_ARRAY_BUFFER, 0, 4*sizeof(GLfloat), data);
glGetBufferSubData(GL_ARRAY_BUFFER, 24*sizeof(GLfloat), 4*sizeof(GLfloat), data);
data[0] *= factor;
glBufferSubData(GL_ARRAY_BUFFER, 24*sizeof(GLfloat), 4*sizeof(GLfloat), data);
redraw();
add_output("push Fl_Gl_Window::pixels_per_unit()=%.1f\n", pixels_per_unit());
return 1;
}
return retval;
}
void reset(void) { shaderProgram = 0; gl_texture_reset(); }
};
void toggle_double(Fl_Widget *wid, void *data) {
static bool doublebuff = true;
doublebuff = !doublebuff;
SimpleGL3Window *glwin = (SimpleGL3Window*)data;
int flags = glwin->mode();
if (doublebuff) flags |= FL_DOUBLE; else flags &= ~FL_DOUBLE;
glwin->reset();
glwin->hide();
glwin->mode(flags);
glwin->show();
}
Fl_Text_Display *output; // shared between output_win() and add_output()
void output_win(SimpleGL3Window *gl)
{
output = new Fl_Text_Display(300,0,500, 280);
Fl_Light_Button *lb = new Fl_Light_Button(300, 280, 500, 20, "Double-Buffered");
lb->callback(toggle_double);
lb->user_data(gl);
lb->value(1);
output->buffer(new Fl_Text_Buffer());
}
void add_output(const char *format, ...)
{
va_list args;
char line_buffer[10000];
va_start(args, format);
vsnprintf(line_buffer, sizeof(line_buffer)-1, format, args);
va_end(args);
output->buffer()->append(line_buffer);
output->scroll(10000, 0);
output->redraw();
}
void button_cb(Fl_Widget *widget, void *) {
add_output("run %s callback\n", widget->label());
}
void add_widgets(Fl_Gl_Window *g) {
Fl::set_color(FL_FREE_COLOR, 255, 255, 255, 140); // partially transparent white
g->begin();
// Create here widgets to go above the GL3 scene
Fl_Button* b = new Fl_Button( 0, 0, 60, 30, "button");
b->color(FL_FREE_COLOR);
b->box(FL_DOWN_BOX );
b->callback(button_cb, NULL);
Fl_Button* b2 = new Fl_Button( 0, 170, 60, 30, "button2");
b2->color(FL_FREE_COLOR);
b2->box(FL_BORDER_BOX );
b2->callback(button_cb, NULL);
g->end();
}
int main(int argc, char **argv)
{
Fl::use_high_res_GL(1);
Fl_Window *topwin = new Fl_Window(800, 300);
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");
topwin->show(argc, argv);
Fl::run();
}
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