theme definition bug

[Yogibear]

During experimenting with themes, i found something i consider to be a bug:

If you define a panel at the bottom of the window, set yanchor to "fixed" and start the application in a window, it crashes without error message.

The reason for this is found in theme::object::location where it says:
relative_loc_.h = minimum<int>(relative_loc_.h, screen.h - relative_loc_.y);

This might result in being zero and leads to a "division by zero"-error in scale_surface(...) later on, which gets not caught.

So i suggest to either prevent h from becoming zero or check zero values in scale_surface (or even in the macro fxpdiv). Of course, this applies to the width as well.

[ott]

[Moved to a more appropriate forum.]

This problem is endemic throughout the code. Basically, there is an assumption that the values for height/width/x/y are benign. We could just slap a wassert(h>0 && w >0) into scale_surface(), but that would simply crash with an assertion instead of division by 0, so no real progress there.

There are 15 different places that scale_surface() is used in the code. I started looking at ways to clean this up, but saw no clean way to do so. It looks like we will have to trace where each w/x/y/h passed as an argument to scale_surface() is initialised, and ensure sanity checking at those points. We need to make sure that the preference values for screen resolution are reasonable (ie. x != 0 and y != 0, since some SDL implementations may be OK with asking for a 0x0 surface), and that the attributes of rectangles specified in theme files are reasonable.