Perform continuous animation with GLFW - opengl

Question

I want to use OpenGL to implement an animation that can be started and paused with mouse clicks. Since I am currently using the GLFW, the functions in GLUT are no longer applicable.
In GLUT, the implementation can be like this:
void windowMouse(int button, int state, int x, int y) {
if (button == GLUT_LEFT_BUTTON && state == GLUT_DOWN) {
// start
glutIdleFunc(idleFunction);
}
else if (button == GLUT_RIGHT_BUTTON && state == GLUT_DOWN) {
// pause
glutIdleFunc(NULL);
}
}
However, glutIdleFunc() does not work in GLFW. I just wrote a coding frame to perform my goal but got stuck in finding the proper function to replace glutIdleFunc().
void mouse_button_callback(GLFWwindow* window, int button, int action, int mode)
{
if (button == GLFW_MOUSE_BUTTON_LEFT && action == GLFW_PRESS)
{
// start
}
else if (button == GLFW_MOUSE_BUTTON_RIGHT && action == GLFW_PRESS)
{
// pause
}
}
Is there any function in GLFW that can replace the previous one? Or is there any way to perform continuous animation with GLFW?

Answer 1

Get creative with glfwPostEmptyEvent() and glfwWaitEventsTimeout():
// g++ main.cpp `pkg-config --cflags --libs glfw3 gl`
#include <GLFW/glfw3.h>
void (*idleFunc)(GLFWwindow*) = nullptr;
void idle( GLFWwindow* aWindow )
{
static float angle = 0.0f;
static double prvTime = glfwGetTime();
const double curTime = glfwGetTime();
const double dt = (curTime - prvTime);
prvTime = curTime;
angle += 60.0 * dt;
int w, h;
glfwGetFramebufferSize( aWindow, &w, &h );
glViewport( 0, 0, w, h );
glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );
glMatrixMode( GL_PROJECTION );
glLoadIdentity();
glMatrixMode( GL_MODELVIEW );
glLoadIdentity();
glPushMatrix();
glRotatef( angle, 0, 0, 1 );
glBegin(GL_TRIANGLES);
glColor3ub( 0, 255, 0 );
glVertex2f( -0.5, -0.5 );
glVertex2f( 0.5, -0.5 );
glVertex2f( 0.0, 0.5 );
glEnd();
glPopMatrix();
glfwSwapBuffers( aWindow );
}
void display( GLFWwindow* aWindow )
{
int w, h;
glfwGetFramebufferSize( aWindow, &w, &h );
glViewport( 0, 0, w, h );
glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );
glMatrixMode( GL_PROJECTION );
glLoadIdentity();
glMatrixMode( GL_MODELVIEW );
glLoadIdentity();
glBegin(GL_TRIANGLES);
glColor3ub( 255, 0, 0 );
glVertex2f( -0.5, -0.5 );
glVertex2f( 0.5, -0.5 );
glVertex2f( 0.0, 0.5 );
glEnd();
glfwSwapBuffers( aWindow );
}
void button( GLFWwindow* window, int button, int action, int mode )
{
if (button == GLFW_MOUSE_BUTTON_LEFT && action == GLFW_PRESS)
{
idleFunc = idle;
glfwPostEmptyEvent();
}
else if (button == GLFW_MOUSE_BUTTON_RIGHT && action == GLFW_PRESS)
{
idleFunc = nullptr;
glfwPostEmptyEvent();
}
}
int main( int, char** )
{
glfwInit();
GLFWwindow* window = glfwCreateWindow( 640, 480, "GLFW", NULL, NULL );
glfwMakeContextCurrent( window );
glfwSetMouseButtonCallback( window, button );
while( !glfwWindowShouldClose( window ) )
{
if(idleFunc)
{
idleFunc(window);
glfwWaitEventsTimeout(0.016);
}
else
{
display(window);
glfwWaitEvents();
}
}
glfwTerminate();
}
The glfwPostEmptyEvent() along with the structure of the glfwWindowShouldClose() loop in main() lets you simulate the behavior of glutPostRedisplay() and the glfwWaitEventsTimeout() lets the idleFunc() (if any) run every 16 milliseconds or so.