# Incorporating window aspect ratio into drawing window

I have a window in my C++ app that I use to draw something.  I'll call this "something" a "model".  My window is NOT a perfect square.  It is wider than it is taller.  It's about 4 times wider than it is tall.  I am having trouble wrapping my brain around how to set the window dimensions, such that the model I draw within the window will be scaled correctly.

If the model I want to draw is taller than it is wide, this is easy to draw.  I just make the window dimensions in the vertical direction equal to the model's height.  Then, I make the window's horizontal dimensions be equal to the model's height times 4 (because the window's aspect ratio is 4). This works fine.

But, if the model I want to draw is wider than it is taller, I am having difficulty.  I could just make the window's vertical dimension be equal to the model's horizontal dimension, and make the window's horizontal dimension be equal to the model's horizontal dimension times 4.  This scales my model wit proper proportion.  However, it makes my model draw too small, because the window's dimensions are much bigger than they need to be.

Any help would be greatly appreciated.
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Commented:
In any given size of model or window there are two possiblities, the model fits the window either vertically or horizontally.  To do the fitting I assume you use some kind of zoom factor at the moment?  Compare the zoom for model width into window width and model height into window height and choose the one which is best.  That would typically be the smaller of the two.

For example lets say the window is 100 pixels wide by 30 pixels high, the model is 50 (somethings) wide by 20 tall.

Horizontal = 100 / 50 = 2
Vertical = 30 / 20 = 1.5

Vertical is less than horizontal so this model fits the window vertically at a zoom of 1.5

Window is 100 X 30 again, this time model is 80 x 15

Horizontal = 100 / 80 = 1.25
Vertical = 30 / 15 = 2

This time horizontal is less than vertical, so the model fits horizontally, at zoom 1.25.

I can explain more details of how to apply this if needs be, it depends on what graphics system you are using.

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