Volume 6A: Motif Programming Manual

cell_height; /* When the user resizes the frame bigger, expose events are generated, * so that's not a problem, since

the expose handler will repaint the * whole viewport. However, when the window resizes smaller, no * expose event

is generated. The window does not need to be * redisplayed if the old viewport was smaller than the pixmap. * (The

existing image is still valid−−no redisplay is necessary.) * The window WILL need to be redisplayed if: * 1) new view

size is larger than pixmap (pixmap needs to be centered). * 2) new view size is smaller than pixmap, but the OLD

view size was * larger than pixmap. */ if ((int) new_height >= rows) { /* The height of the viewport is taller than the

pixmap, so set * pix_voffset = 0, so the top origin of the pixmap is shown, * and the pixmap is centered vertically in

viewport. */ pix_voffset = 0; sw_voffset = (view_height − rows * cell_height)/2; /* Case 1 above */ do_clear = True;

/* scrollbar is maximum size */ new_height = rows; } else { /* Pixmap is larger than viewport, so viewport will be

completely * redrawn on the redisplay. (So, we don't need to clear window.) * Make sure upper side has origin of a

cell (bitmap). */ pix_voffset = min (pix_voffset, (rows−new_height) * cell_height); sw_voffset = 0; /* no centering is

done */ /* Case 2 above */ if (oldh > rows * cell_height) do_clear = True; } XtVaSetValues (vsb, XmNsliderSize,

max (new_height, 1), XmNvalue, pix_voffset / cell_height, XmNpageIncrement, max (new_height−1, 1), NULL); /*

identical ...