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141 lines
4.7 KiB
ReStructuredText
141 lines
4.7 KiB
ReStructuredText
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.. _text-anchors:
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Text anchors
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============
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The ``anchor`` parameter determines the alignment of drawn text relative to the ``xy`` parameter.
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The default alignment is top left, specifically ``la`` (left-ascender) for horizontal text
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and ``lt`` (left-top) for vertical text.
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This parameter is only supported by OpenType/TrueType fonts.
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Other fonts may ignore the parameter and use the default (top left) alignment.
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Specifying an anchor
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^^^^^^^^^^^^^^^^^^^^
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An anchor is specified with a two-character string. The first character is the
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horizontal alignment, the second character is the vertical alignment.
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For example, the default value of ``la`` for horizontal text means left-ascender
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aligned text.
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When drawing text with :py:meth:`PIL.ImageDraw.ImageDraw.text` with a specific anchor,
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the text will be placed such that the specified anchor point is at the ``xy`` coordinates.
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For example, in the following image, the text is ``ms`` (middle-baseline) aligned, with
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``xy`` at the intersection of the two lines:
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.. image:: ../../Tests/images/test_anchor_quick_ms.png
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:alt: ms (middle-baseline) aligned text.
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:align: left
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.. code-block:: python
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from PIL import Image, ImageDraw, ImageFont
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font = ImageFont.truetype("Tests/fonts/NotoSans-Regular.ttf", 48)
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im = Image.new("RGB", (200, 200), "white")
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d = ImageDraw.Draw(im)
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d.line(((0, 100), (200, 100)), "gray")
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d.line(((100, 0), (100, 200)), "gray")
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d.text((100, 100), "Quick", fill="black", anchor="ms", font=font)
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.. container:: clearer
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.. only: comment
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The container above prevents the image alignment from affecting the following text.
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Quick reference
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^^^^^^^^^^^^^^^
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.. image:: ../resources/anchor_horizontal.svg
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:alt: Horizontal text
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:align: center
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.. image:: ../resources/anchor_vertical.svg
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:alt: Vertical text
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:align: center
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Horizontal anchor alignment
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^^^^^^^^^^^^^^^^^^^^^^^^^^^
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``l`` --- left
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Anchor is to the left of the text.
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For *horizontal* text this is the origin of the first glyph, as shown in the `FreeType tutorial`_.
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``m`` --- middle
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Anchor is horizontally centered with the text.
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For *vertical* text it is recommended to use ``s`` (baseline) alignment instead,
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as it does not change based on the specific glyphs of the given text.
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``r`` --- right
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Anchor is to the right of the text.
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For *horizontal* text this is the advanced origin of the last glyph, as shown in the `FreeType tutorial`_.
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``s`` --- baseline *(vertical text only)*
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Anchor is at the baseline (middle) of the text. The exact alignment depends on the font.
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For *vertical* text this is the recommended alignment,
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as it does not change based on the specific glyphs of the given text
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(see image for vertical text above).
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Vertical anchor alignment
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^^^^^^^^^^^^^^^^^^^^^^^^^
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``a`` --- ascender / top *(horizontal text only)*
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Anchor is at the ascender line (top) of the first line of text, as defined by the font.
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See `Font metrics on Wikipedia`_ for more information.
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``t`` --- top *(single-line text only)*
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Anchor is at the top of the text.
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For *vertical* text this is the origin of the first glyph, as shown in the `FreeType tutorial`_.
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For *horizontal* text it is recommended to use ``a`` (ascender) alignment instead,
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as it does not change based on the specific glyphs of the given text.
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``m`` --- middle
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Anchor is vertically centered with the text.
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For *horizontal* text this is the midpoint of the first ascender line and the last descender line.
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``s`` --- baseline *(horizontal text only)*
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Anchor is at the baseline (bottom) of the first line of text, only descenders extend below the anchor.
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See `Font metrics on Wikipedia`_ for more information.
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``b`` --- bottom *(single-line text only)*
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Anchor is at the bottom of the text.
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For *vertical* text this is the advanced origin of the last glyph, as shown in the `FreeType tutorial`_.
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For *horizontal* text it is recommended to use ``d`` (descender) alignment instead,
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as it does not change based on the specific glyphs of the given text.
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``d`` --- descender / bottom *(horizontal text only)*
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Anchor is at the descender line (bottom) of the last line of text, as defined by the font.
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See `Font metrics on Wikipedia`_ for more information.
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Examples
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^^^^^^^^
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The following image shows several examples of anchors for horizontal text.
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In each section the ``xy`` parameter was set to the center shown by the intersection
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of the two lines.
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.. comment: Image generated with ../example/anchors.py
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.. image:: ../example/anchors.png
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:alt: Text anchor examples
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:align: center
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.. _Font metrics on Wikipedia: https://en.wikipedia.org/wiki/Typeface#Font_metrics
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.. _FreeType tutorial: https://freetype.org/freetype2/docs/tutorial/step2.html
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