.PTR

OS/2 pointer (PT)

Introduction

The OS/2 pointer is a black and white mouse pointer stored as a BMP file with the type code PT. It is laid out exactly like a black and white OS/2 icon: one 1-bit bitmap twice the pointer’s height, holding an AND mask and an XOR mask. The two fields that a bitmap reserves give the hotspot, the pixel that marks where the pointer points.

Pointer files are usually named .ptr. A file with versions for several screens is a bitmap array whose entries are PT or colour pointer images.

Software

ArcaOS, the current OS/2, whose Icon Editor opens and saves them
Deark, which converts them to PNG (Windows, macOS, Linux)

Structure

The parts are those of a black and white icon, and the masks combine the same way: black, white, transparent or inverted. All numbers are little-endian.

0File header PT, size, hotspot and the offset of the pixels14 bytes
14DIB header width, double height, 1 bit per pixel12 to 64 bytes
…Colour table two entries, black and white6 or 8 bytes
…Masks 1-bit rows padded to 4 bytes, the AND mask and the XOR mask one above the othervaries

An OS/2 pointer

File header

Offset	Size	Type	Name	Description
0	2	char[2]	`usType`	The signature `PT` (`50 54`).
2	4	u32	`cbSize`	A size field; readers should not depend on it.
6	2	i16	`xHotspot`	The hotspot’s x position within the pointer.
8	2	i16	`yHotspot`	The hotspot’s y position within the pointer.
10	4	u32	`offBits`	The offset from the start of the file to the mask bits.

Telling it apart

The file starts with PT (50 54), and its DIB header gives 1 bit per pixel with a height twice the width. Apart from the type code it is identical to an OS/2 icon. A colour pointer starts with CP and has a second file header.