How to glutDisplayFunc, glutMainLoop in glfw? - c++

Question

I have a small program using glut and i need for many reasons to use glfw now. Since I have never used glfw I have a lot of problems.
The main ones are the functions : glutDisplayFunc, glutReshapeFunc, glutIdleFunc and glutMainLoop. I have just found out that there are no equivalent functions in glfw. How should I modify my program ?
My program is about a cone rotating in 3 dimensions
I have a function displaycone:
void displayCone(void){
// clear the drawing buffer.
glClear(GL_COLOR_BUFFER_BIT); //
// set matrix mode
glMatrixMode(GL_MODELVIEW);
// clear model view matrix
glLoadIdentity();
// multiply view matrix to current matrix
gluLookAt(3.0, 3.0, 3.0-4.5, 0.0, 0.0,-4.5,0,1,0);
// ******
glPushMatrix();
glTranslatef(0.0, 0.0, -4.5);
glBegin(GL_LINES);
glColor3f (1.0, 1.0, 0.0);
glVertex3f(0.0, 0.0, 0.0);
glVertex3f(2.0, 0.0, 0.0);
glColor3f (1.0, 1.0, 0.0);
glVertex3f(0.0, 0.0, 0.0);
glVertex3f(0.0, 2.0, 0.0);
glColor3f (1.0, 1.0, 0.0);
glVertex3f(0.0, 0.0, 0.0);
glVertex3f(0.0, 0.0, 2.0);
glEnd();
glPopMatrix();
// clear the drawing buffer.
// traslate the draw by z = -4.0
// Note this when you decrease z like -8.0 the drawing will looks far , or smaller.
glTranslatef(0.0,0.0,-4.5);
// Red color used to draw.
glColor3f(0.8, 0.2, 0.1);
// changing in transformation matrix.
// rotation about X axis
glRotatef(xRotated,1.0,0.0,0.0);
// rotation about Y axis
glRotatef(yRotated,0.0,1.0,0.0);
// rotation about Z axis
glRotatef(zRotated,0.0,0.0,1.0);
// scaling transfomation
glScalef(1.0,1.0,1.0);
// built-in (glut library) function , draw you a Cone.
// move the peak of the cone to the origin
glTranslatef(0.0, 0.0, -height);
glutSolidCone(base,height,slices,stacks);
// Flush buffers to screen
// gluLookAt(3,3,3,0,0,-4.5,0,1,0); <----------------------- delete
glFlush();
// sawp buffers called because we are using double buffering
// glutSwapBuffers();
}
a function reshapecone:
void reshapeCone(int x, int y)
{
if (y == 0 || x == 0) return; //Nothing is visible then, so return
//Set a new projection matrix
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
//Angle of view:40 degrees
//Near clipping plane distance: 0.5
//Far clipping plane distance: 20.0
gluPerspective(35.0,(GLdouble)x/(GLdouble)y,0.5,20.0);
glViewport(0,0,x,y); //Use the whole window for rendering
}
and a function idleCone:
void idleCone(void)
{
for(int j = 1; j<10000 ; j++){
double i = dati[j+1][0];
int win = glfwGetWindow();
if(i == 0.) break;
xRotated = 180/M_PI*(dati[j][0]);
yRotated = 180/M_PI*(dati[j][1]);
zRotated = 180/M_PI*(dati[j][2]);
displayCone();
xRotated += 0.;
yRotated += 0.;
zRotated += 0.;
displayCone();
}
}
In my previous program i had in main:
glfwInit(&argc, argv);
//double buffering used to avoid flickering problem in animation
glutInitDisplayMode(GLUT_SINGLE | GL_RGB);
//glfwInitWindowSize(800,700);
glfwCreateWindow(800,700,"Rotation of the top",NULL,NULL);
glPolygonMode(GL_FRONT_AND_BACK,GL_LINE);
xRotated = yRotated = zRotated = 0.0;
xRotated=0.0;
yRotated=0.0;
glClearColor(0.0,0.0,0.0,0.0);
glutDisplayFunc(displayCone);
glutReshapeFunc(reshapeCone);
glutIdleFunc(idleCone);
glutMainLoop();

Answer 1

When using glfw, then you've to create your own application loop. Note, it is important to to make the OpenGL context current, before calling any OpenGL instruction, by glfwMakeContextCurrent. e.g.:
GLFWwindow *wnd = glfwCreateWindow(800,700,"Rotation of the top",NULL,NULL);
glfwMakeContextCurrent(wnd);
// do the OpenGL initialization
// [...]
while (!glfwWindowShouldClose(wnd))
{
// do the drawing
displayCone();
glfwSwapBuffers(wnd);
glfwPollEvents();
}
Instead of glutReshapeFunc you can set the size callback by glfwSetWindowSizeCallback: e.g.:
glfwSetWindowSizeCallback(wnd, reshapeCone);
void reshapeCone(GLFWwindow* window, int x, int y)
{
// [...]
}