glk_window_get_size ()

void
glk_window_get_size (winid_t win,
                     glui32 *widthptr,
                     glui32 *heightptr);

Simply returns the actual size of the window, in its measurement system. As described in Other API Conventions, either widthptr or heightptr can be NULL, if you only want one measurement.

glk_window_set_arrangement ()

void
glk_window_set_arrangement (winid_t win,
                            glui32 method,
                            glui32 size,
                            winid_t keywin);

Changes the size of an existing split — that is, it changes the constraint of a given pair window.

Consider the example above, where D has collapsed to zero height. Say D was a text buffer window. You could make a more useful layout by doing

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winid_t o2;
o2 = glk_window_get_parent(d);
glk_window_set_arrangement(o2, winmethod_Above | winmethod_Fixed, 3, d);

That would set D (the upper child of O2) to be O2's key window, and give it a fixed size of 3 rows.

If you later wanted to expand D, you could do

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glk_window_set_arrangement(o2, winmethod_Above | winmethod_Fixed, 5, NULL);

That expands D to five rows. Note that, since O2's key window is already set to D, it is not necessary to provide the keywin argument; you can pass NULL to mean “leave the key window unchanged.”

If you do change the key window of a pair window, the new key window must be a descendant of that pair window. In the current example, you could change O2's key window to be A, but not B. The key window also cannot be a pair window itself.

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glk_window_set_arrangement(o2, winmethod_Below | winmethod_Fixed, 3, NULL);

This changes the constraint to be on the lower child of O2, which is A. The key window is still D; so A would then be three rows high as measured in D's font, and D would get the rest of O2's space. That may not be what you want. To set A to be three rows high as measured in A's font, you would do

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glk_window_set_arrangement(o2, winmethod_Below | winmethod_Fixed, 3, a);

Or you could change O2 to a proportional split:

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glk_window_set_arrangement(o2, winmethod_Below | winmethod_Proportional, 30, NULL);

or

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glk_window_set_arrangement(o2, winmethod_Above | winmethod_Proportional, 70, NULL);

These do exactly the same thing, since 30% above is the same as 70% below. You don't need to specify a key window with a proportional split, so the keywin argument is NULL. (You could actually specify either A or D as the key window, but it wouldn't affect the result.)

Whatever constraint you set, glk_window_get_size() will tell you the actual window size you got.

Note that you can resize windows, and alter the Border/NoBorder flag. But you can't flip or rotate them. You can't move A above D, or change O2 to a vertical split where A is left or right of D.

glk_window_get_arrangement ()

void
glk_window_get_arrangement (winid_t win,
                            glui32 *methodptr,
                            glui32 *sizeptr,
                            winid_t *keywinptr);

Queries the constraint of a given pair window.