= Modifying a standard Qt image plugin =

I created a Qt image format plugin to write CCITT-compressed TIFF files by
stripping out everything that wasn't needed from the standard TIFF plugin
in Qt.

Here's a recipe for those of you interested in doing the same thing:

 1. Locate the src/plugins/imageformats/tiff directory in the Qt source package.
 2. Copy it, creating a new directory called tiff_ccitt for the modifications.
 Make the following modifications to files in that directory.
 3. Apply the [[attachment:tiff_ccitt.patches|set of patches]] to the files in that directory, typically by entering the directory at the command line and typing

 {{{patch < tiff_ccitt.patches
 }}}

Now, you should be able to build the plugin by typing the following commands:

{{{qmake
make
make install
}}}

Note that, on some GNU/Linux systems, you might need to run `qmake-qt4` instead of `qmake` and that you may need root privileges to invoke `make install`.

With the plugin installed, you should be able to write TIFF images using the `tiff_ccitt_group4` format. The following code can be used as a test:

{{{#!/usr/bin/env python

import sys
from PyQt4.QtGui import *

app = QApplication([])

image = QImage(200, 200, QImage.Format_Mono)
image.fill(qRgb(255,255,255))

painter = QPainter()
painter.begin(image)
painter.setPen(QColor(0,0,0))
painter.drawRect(20,20,160,160)
painter.end()

writer = QImageWriter()
if not writer.setFormat("tiff_ccitt_group4"):
    sys.stderr.write("Failed to set the format for the plugin.\n")
    sys.exit(1)

writer.setFileName("temp-sq.tif")
writer.write(image)
}}}