Question

When I resize a window, I can do so using the top,bottom,left or right sides or top-right,top-left,bottom-right or bottom-left corners.

Is there a way to know which one is used when I’m resizing?

Answer 1

I don’t know if there is an elegant solution because different operating systems handle borders differently.

My suggestion is

• to compute the difference between the current and previous window size each time it is drawn
• Get the mouse cursor’s position.
• If the window X changes, the border used is probably the left or right — whichever the mouse cursor is closest to. If the Y changes, probably the top or bottom border the cursor is closest to.
• If both change, the corner the mouse cursor is closest to is probably it.

A few corner cases may come up. For example, a window can be resized on some systems using the keyboard. It can potentially also be resized programatically, like when the user changes to a resolution too low to contain your window. These things can be handled in most cases by detecting of the mouse button is clicked while the resize is taking place.

Also, it is possible to resize just the width or height from the corner. In these cases, you may have to choose a threshold for mouse distance from corner that would decide whether it is actually at a corner.