How to detect when left mouse button is released in GLUT after being held in motion?

Question

I am trying to detect when my left mouse button is released to store the result in a boolean variable in OpenGL GLUT. Currently, I am using the motion() function in glutMotionFunc(motion); and setting the boolean variable bool mouseIsHeldDown to true when the left mouse button is held in motion to trigger an if statement in my render function myDisplay(). However, I cannot find an efficient way to find when the left mouse button is released to declare the same variable as false.

Any ideas? Is there a way in Win32?

int main(int argc, char* argv[]) 
{
    ...
    glutMotionFunc(motion);
    ...
}

void motion(int x, int y)
{
    mouseIsHeldDown = true;
}

void myDisplay() 
{
    if (mouseIsHeldDown == true)
    {
        
    }
}

Answer 1

One common method is to store the LAST mouse button pressed and then test if the last state was not pressed compared to the current state.

E.g.

bool lastButtonState = false;

void readInput() {
     bool curButtonState = readButton();     

     // Detect "rising" edge of button (AKA, pressed)
     if(curButtonState == true && curButtonState != lastButtonState) {
         doStuff();
     }

     // Update last state for next call..
     lastButtonState = curButtonState;
}

You can also detect if the button was released using this method.

e.g.

if(curButtonState == false && curButtonState != lastButtonState)
    doStuffRelatedToButtonRelease();

Note: readInput() should be called once per frame because it keeps a copy of the current frames input state.

EDIT: The above example is a general solution, below is a solution specific to GLUT as per your update. You need to use the mouse() function to read the button state, motion() doesn't have the needed button state information. GLUT already tells you if that was pressed (transition from false->true) or released (transition from true->false) via the "state" variable.

void mouse(int button, int state, int x, int y)
{
    if (button == GLUT_LEFT_BUTTON) {
        if(state == GLUT_DOWN) 
            onLeftButtonPressed();    // do your thing here..

        // You can also test for (state == GLUT_UP) for mouse button release..
    }
}