XPLM_API void       XPLMSetWindowResizingLimits(
                         XPLMWindowID         inWindowID,    
                         int                  inMinWidthBoxels,    
                         int                  inMinHeightBoxels,    
                         int                  inMaxWidthBoxels,    
                         int                  inMaxHeightBoxels);    

Sets the minimum and maximum size of the client rectangle of the given window. (That is, it does not include any window styling that you might have asked X-Plane to apply on your behalf.) All resizing operations are constrained to these sizes.

Only applies to modern windows. (Windows created using the deprecated XPLMCreateWindow(), or windows compiled against a pre-XPLM300 version of the SDK will have no minimum or maximum size.)