Text Layout

Mapping a text string to screen coordinates within a widget is called text layout. The Text widget’s default layout class supports aligning text to the left, center or right, and can wrap text on space characters, at any location, or clip text that is off the edge.

Text("Showing some different alignment modes", align=...)

align='left' (default)
+----------------+   +------------------------+
|Showing some    |   |Showing some different  |
|different       |   |alignment modes         |
|alignment modes |   +------------------------+

+----------------+   +------------------------+
|  Showing some  |   | Showing some different |
|   different    |   |    alignment modes     |
|alignment modes |   +------------------------+

+----------------+   +------------------------+
|    Showing some|   |  Showing some different|
|       different|   |         alignment modes|
| alignment modes|   +------------------------+
Text("Showing some different wrapping modes\nnewline", wrap=...)

wrap='space' (default)
+----------------+   +------------------------+
|Showing some    |   |Showing some different  |
|different       |   |wrapping modes          |
|wrapping modes  |   |newline                 |
|newline         |   +------------------------+

+----------------+   +------------------------+
|Showing some dif|   |Showing some different w|
|ferent wrapping |   |rapping modes           |
|modes           |   |newline                 |
|newline         |   +------------------------+

+----------------+   +------------------------+
|Showing some dif|   |Showing some different w|
|newline         |   |newline                 |
+----------------+   +------------------------+

If this is good enough for your application feel free to skip the rest of this section.

Custom Text Layouts

The StandardTextLayout is set as the class variable Text.layout. Individual Text widgets may use a different layout class, or you can change the default by setting the Text.layout class variable itself.

A custom text layout class should extend the TextLayout base class and return text layout structures from its layout() method.

Text Layout Structures

"This is how a string of text might be displayed"

0----5---10---15---+   right_aligned_text_layout = [
|     This is how a|     [(5, 0), (13, 0, 13)],
|    string of text|     [(4, 13), (14, 14, 28)],
|might be displayed|     [(18, 29, 47)]
+------------------+   ]

The mapping from a text string to where that text will be displayed in the widget is expressed as a text layout structure.

Text layout structures are used both for rendering Text widgets and for mapping (x, y) positions within a widget back to the corresponding offsets in the text. The latter is used when moving the cursor in Edit widgets up and down or by clicking with the mouse.

A text layout structure is a list of one or more line layouts. Each line layout corresponds to a row of text in the widget, starting from its top.

A line layout is a list zero or more of the following tuples, each expressing text to be displayed from left to right:

  1. (column width, starting text offset, ending text offset)
  2. (column width of space characters to insert, text offset or None)
  3. (column width, text offset, new text to insert)``

Tuple A displays a segment of text from the Text widget. Column width is explicitly specified because some characters within the text may be zero width or double width.

Tuple B inserts any number of space characters, and if those characters correspond to an offset within the text, that may be specified.

Tuple C allows insertion of arbitrary text. This could be used for hyphenating split words or any other effect not covered by A or B. The StandardTextLayout does not currently use this tuple in its line layouts.

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