DWriteShapePy is a Python extension built using Cython. It provides streamlined bindings for the DirectWrite shaping engine. The model is similar to the model provided by uHarfBuzz but some differences because of differences in the API models between DirectWrite and HarfBuzz.

DWriteShapePy was initially developed to support a Python based font testing environment where similar tests are executed using both DirectWrite and HarfBuzz.

The repo contains two methods to build the extension. The standard Python/Cython method using setup.py and a Visual Studio solution. Setup.py is used to build, install and create distribution packages. The Visual Studio solution is for cross mode debugging of the extension as well as the client.

Setup.py builds the package with the extension name “dwriteshapepy”. Useful command lines when using setup.py to build, install and create distribution packages are:

Build the extension on local machine. Python setup.py build

Install the built extension into current Python environment. Python setup.py install

Create distribution package. Python setup.py bdist_wheel

The dwriteshape directory in the repo contains the Visual Studio solution and projects. The dwriteshape solution contains two projects. The dwriteshape project and the client project. The dwriteshape project builds the package as the extension name “dwriteshape”. Note the difference between extension build using setup.py. This is necessary because Visual Studio does not have same level of control as setup.py and seems to require the extension name be the same as that of the .pyx file. It could also be useful in avoiding name collisions. The Visual Studio project should only be used to create debug builds of the extension for development. The client project is a simple test client for the dwriteshape project.

In order to build the extension with the Visual Studio project you must first use Cython to create the .cpp file from the .pyx and .pxd files. There is a build.bat in the src\dwriteshapepy directory to do this. The generated file dwriteshape.cpp should be deleted if switching from building with Visual Studio or setup.py or visa versa. When building with setup.py the .cpp file is generated automatically so build.bat is not necessary.

The directory src\cpp contains the DWrite abstraction layer of the extension basically plumbing between the exported API and DWrite. This code is common between build methods.

import sys
import dwriteshapepy as dw 
from pathlib import Path

with open(sys.argv[1], 'rb') as fontfile:
    fontdata = fontfile.read()

text = sys.argv[2]

face = dw.Face(fontdata)
font = dw.Font(face)
upm = font.upem
print(upm)

buf = dw.Buffer()
buf.add_str(text)
    
features = {"kern": True, "liga": True}
dw.shape(font, buf, features)
glyph_names = [font.glyph_to_string(g.codepoint) for g in buf.glyph_infos]
infos = [(g.codepoint, g.cluster) for g in buf.glyph_infos]
print(glyph_names)
print(infos)

advance = [(adv.x_advance, adv.y_advance, adv.x_offset, adv.y_offset) for adv in buf.glyph_positions]
print(advance)

infos = buf.glyph_infos
positions = buf.glyph_positions

for info, pos in zip(infos, positions):
    gid = info.codepoint
    cluster = info.cluster
    x_advance = pos.x_advance
    x_offset = pos.x_offset
    y_offset = pos.y_offset
    print(f"gid{gid}={cluster}@{x_advance},{x_offset}+{y_offset}")

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