Working with Windows mouse event states in c++ VS2012 - 13 - c++

Question

I am working on a GameEngine Project and my framework is as follows I have an Engine Class that is a base class that creates a window and setups up an open GL context and handles windows message events. From this I have a derived class that is a Game class. Some functions are purely virtual. My project is too large to post here so I will show code segments that are relevant.
I am working within these two classes and the task I am trying to achieve is to make an object fade in and out of view with a left mouse click. The position of the mouse cursor is irrelevant. This can easily be done by changing the alpha value from 1.0f to 0.0f. The object is initially visible and when the first mouse click & release operation happens I need it to fade out. Then the next time the mouse button is pressed & released I need it to fade back into view to full opacity. I am stuck at this point.
This is the section of my Engine::messageHandler() that is of importance
Engine::MessageHandler( unsigned uMsg, WPARAM wParam, LPARAM lParam ) {
switch( uMsg ) {
// ... Irrelevant Code Here
case WM_LBUTTONDOW: {
m_mouseState.isButtonPressed[MOUSE_LEFT_BUTTON] = true;
mouseInput(); // purely virtual - implemented by Game class
return true;
}
case WM_LBUTTONUP: {
m_mouseState.isButtonPressed[MOUSE_LEFT_BUTTOM] = false;
mouseInput(); // purely virtual - implemented by Game class
return true;
}
// ... More Irrelevant Code Here
default {
return false;
}
}
} // messageHandler
It is in my Game::mouseInput() function where I need to change the alpha value of my rendered object with a mouse click & release operation.
void Game::mouseInput() {
} // mouseInput
And I have tried if statements & while loops to no avail.
I was able to get the object to fade by an incremental amount each time as I continued to clicking the left mouse button. The code looked something like this
Game::mouseInput {
static glm::vec4 sliceColor = m_pSliceFade->getColor();
if ( m_mouseState.isButtonPressed[MOUSE_LEFT_BUTTON] == true ) {
sliceColor.a -= 0.05f;
m_pSliceFade->setColor( sliceColor );
}
} // mouseInput
However, this is not the behavior I want or need. I am struggling here because each time we go into the Engine::messageHandler() for both mouse down & up events my purely virtual Game::mouseInput() is being called. I guess I am having writers block because I can not seem to figure out how to continuously change the alpha value after each click & release event and then reverse the direction of the alpha value on the following click & release event within this framework. Initially all mouse buttons bool tracking variables are set to false by default on initialization.
Any kind of suggestions or help would be supportive and helpful. Thank you kindly in advance.