Windows Paintbrush File Format

The information in this article applies to:

• Microsoft Windows Software Development Kit (SDK) for Windows versions 3.1 and 3.0

SUMMARY

This article provides the format of Windows Paintbrush files.

MORE INFORMATION

Paintbrush files are preceded by 32 bytes of header information. Following the header is an index table into run-length encoded data.

Header

The header structure is defined in the C programming language, as follows:

typedef struct {

  WORD  key1;
  WORD  key2;
  WORD  dxFile;
  WORD  dyFile;

  /* NOTE: PBRUSH.EXE version 3.0 and 3.1 ignore the remaining values */
  /* in this structure. Future versions may or may not.               */

  WORD  ScrAspectX;
  WORD  ScrAspectY;
  WORD  PrnAspectX;
  WORD  PrnAspectY;
  WORD  dxPrinter;
  WORD  dyPrinter;
  WORD  AspCorX;
  WORD  AspCorY;
  WORD  wCheck;
  WORD  res1;
  WORD  res2;
  WORD  res3;
  WORD  res4;

The first 32 bytes contain the header information described by the above structure:

Bytes   Name     Win 1.0   Win 2.0           Win 3.0
-----   ----     -------   -------           -------

0 - 1   Key1     0x6144    0x694C      |0x6144| or |0x694C|
2 - 3   Key2     0x4D6E    0x536E      |0x4D6E|    |0x536E|

4 - 5   dxFile      X-dimension size of bitmap, in pixels

6 - 7   dyFile      Y-dimension size of bitmap, in pixels

8 - 9   SrcAspectX  Aspect ratio of the screen for which file was
                    created. Obtained from GetDeviceCaps(hScreenDC,
                    ASPECTX);

                    created. Obtained from GetDeviceCaps(hScreenDC,
                    ASPECTY);

                    created. Obtained from GetDeviceCaps(hPrinterDC,
                    ASPECTX);

                    created. Obtained from GetDeviceCaps(hPrinterDC,
                    ASPECTY);

16 - 17 dxPrinter   Resolution of the printer for which file was
                    created. Contains the number of pixels in the x
                    direction on the printer. The selected paper and
                    printer orientation affect this value.

18 - 19 dyPrinter   Resolution of the printer for which file was
                    created. Contains the number of pixels in the y
                    direction on the printer. The selected paper and
                    printer orientation affect this value.

20 - 21 AspCorX     Not used. Set to zero.

22 - 23 AspCorY     Not used. Set to zero.

24 - 25 wCheck      Checksum field. Makes sure that this file is Paint
                    format.

Index

The Paintbrush bitmap is run-length encoded. Each scan line is encoded separately. The length of the resulting encoded string depends on the pattern of the bitmap. There is an index table following the header. Each entry of this index corresponds to a scan line. It is an unsigned integer and shows the length of the encoded data. Following this table is the encoded data.

   32 - xxx     xxx = 32 + sizeof(unsigned int) * dyPrinter

ALGORITHM FOR ENCODING

Paint encoding is read in BYTES. There are two types of encoded data: one starts with 0 (zero), the other starts with a nonzero value.

If the data starts with 0, it is a repeated byte pattern. The byte following the 0 tells how many times to repeat the pattern and the subsequent byte is the pattern itself. For example, 0, 0x80, 0xff, should be expanded to eighty (hex) bytes of 0xff.

If the data starts with a nonzero value, X, the following X number of bytes contain unmodified bitmap data, without recognizable pattern. Each scan line can be composed of several of the above mentioned groups of data. Of course, the groups should alternate, meaning that a scan line can start with a repeated pattern followed by some random pattern, which is followed by another repeated pattern.

To reach the data for the nth scan line, add up the values in the index table from entry 0 to entry n - 1.