|Location||ATARI_REXT (v2.25+), SMSQ/E|
This function returns the number of bytes required to hold one line of pixels on the current screen resolution attached to the specified channel (default #0). On a standard QL 512x256 resolution, this is normally 128 bytes but can alter on other resolutions.
As with SCR_BASE, if the specified channel is not open then Invalid Channel ID will be reported. However, if no channel is specified and #0 is not open, then a special window will be opened for #0 on screen, which may destroy what is already on screen.
You should never assume that the number of bytes required to store a line is the number of pixels DIV 4 - always use this function instead.