skia-harfbuzz

A Python library that helps to draw text in skia-python with harfbuzz shaping engine.

Features Preview

The library integrates with uharfbuzz to support font features like kerning and ligatures. Here are some showcases for harfbuzz-integrated text shaping.

For more information about font features, see this.

Kerning

Kerning refers to the spacing between specific glyph pairings.

Ligatures

Ligatures are glyphs that replace two or more separate glyphs in order to represent them more smoothly (from a spacing or aesthetic perspective). Ligatures are necessary in certain language scripts.

Usage

Install

The Python package is available on PyPI.

pip install skia-harfbuzz

If you are using Linux, make sure you have correctly configured the environment for skia-python.

Use Library API

Create Typeface and Font

from skia_harfbuzz import SkiaHarfbuzzTypeface, SkiaHarfbuzzFont

font_path = '/path/to/your_font.ttf'
typeface = SkiaHarfbuzzTypeface.create_from_file(font_path)
# Or use font data
# with open(font_path, 'r') as f:
#     typeface = SkiaHarfbuzzTypeface.create_from_data(f.read())

font: SkiaHarfbuzzFont = typeface.create_font(size=20.0)
# Optionally, set scaleX, skewX and font features
# font = typeface.create_font(size=20.0, scale_x=1.1, skew_x=-0.10, features={ 'calt': False })

Draw and Measure

SkiaHarfbuzzFont provides the following functions to measure and draw text:

• measure_text(text, bounding_box): returns the advance width of text, and optionally a bounding box relative to origin (0, 0)
• draw_text(canvas, text, x, y, paint, anchor_x, anchor_y): draws text with given options

The value of anchor_x and anchor_y indicates the position type of input x and y. By default, x is considered the left coordinate and y is considered the baseline coordinate (same as skia API).

AnchorTypeX: left, center, right

AnchorTypeY: baseline, top, center, bottom

Patch Skia

Patch skia to override typeface loading and basic text rendering. Then you can continue with you old code.

from skia_harfbuzz import patch_skia

patch_skia()

After patching, skia typeface created by Typeface.MakeFromPath or Typeface.MakeFromData will manage its companion harfbuzz typeface. The companion harfbuzz typeface is deleted when the typeface is garbage collected.

The following APIs are patched to work with harfbuzz:

• Canvas.drawString
• Canvas.drawSimpleText
• Font.measureText

Limitations

There are some limitations that you may need to take care when using:

• Paint argument in patched Font.measureText is not supported. This ignores stroke width and path effect, etc.
• Minor font settings (e.g. embolden) not considered.