From QB64 Wiki
The _HEIGHT function returns the height of an image handle or current write page.
- result& = _HEIGHT[(imageHandle&)]
- If imageHandle& is omitted, it's assumed to be the handle of the current write page.
- To get the width of the current program window use zero for the handle value: depth& = _HEIGHT(0)
- If the image specified by imageHandle& is in text mode, the number of characters per column is returned.
- If the image specified by imageHandle& is in graphics mode, the number of pixels per column is returned.
- If imageHandle& is an invalid handle, then an invalid handle error will occur.
- The maximum pixel coordinate of a program screen is one less than what the function returns.
Example: Displays the current program window area.