This message can be used to change the size of the grid squares after a grid has been created.

The only fields in the GRIDINFO structure that can be set by the application are the cb, cxGrid, cyGrid, and pGrid fields. If the cxGrid and cyGrid fields are nonzero and the pGrid field is NULL, the container creates a grid with grid squares of width cxGrid and height cyGrid.

If cxGrid and cyGrid are zero, the container will create default size grid squares. It is not necessary to send this message to create default size grid squares, because they will be created the first time an arrange with the CM_ARRANGEGRID option is performed.

The application can completely control the placement of icons by marking the squares it wants occupied and then sending the CM_ARRANGE message with mp1 equal to CMA_ARRANGEGRID and mp2 equal to CMA_USER. Here is how the application uses CM_SETGRIDINFO to mark the squares:

• If the pGrid field of the GRIDINFO structure is non-NULL, the container expects a pointer that points to an array of GRIDSQUARE structures, one for each available grid square in the grid. In this case, the cxGrid and cyGrid fields are ignored.

• The container uses the grid square array to mark the grid squares as available or unavailable. If the ulState field of the GRIDSQUARE structure is marked CMA_AVAIL, the square can be occupied by an icon; if it is marked CMA_UNAVAIL, it is not available.

Marking of grid squares is used only when the arrangement pattern is CMA_USER and has no effect on the placement of icons when any other pattern is specified.