I have trouble understanding the way a camera is set in Processing (according to the reference this shoudn't be very different from OpenGl). For starters, when I set the eye position of the camera I have to set three coordinates. I'm assuming that the X coordinate is the horizontal border of the display and the Y coordinate would be the vertical border. I think the Z coordinate to be behind or in front my computer.
So when I do:
camera(width/2, height/2, depth, 250, 250, 0, 0, 1, 0);
I'm setting the camera in the middle of the display and putting it some depth in the axis that comes into my eyes.
I think this part is clear enough. However, the two other parameters are not as clear. In particular in don't see the difference between the center of the scene and the last parameter which is the axis that is facing upward.
For the center of the scene I'm assuming that it gives me the direction the camera is looking to but what is the axis that is facing upward?