Miscellaneous functions in Automation 4

This document describes various functions that couldn't be placed in any of
the other Automation 4 documents.

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Getting the rendered size of a string

This function might later on be part of a full rendering-interface for
creating actual bitmaps of text.

This function does NOT attempt to handle line breaks, automatic line breaking,
fomatting override tags, vector drawings or anything else to that effect.
If you need such functionality, you need to implement it yourself. (For now,
at least.)

function aegisub.text_extents(style, text)

@style (table)
  A "style" class Subtitle Line table. This 

@text (string)
  The text to calculate the rendered size of.

Returns: 4 values, all numbers.
  1. Width of text in pixels.
  2. Height of text in pixels.
  3. Descent of text in pixels.
  4. External leading of text in pixels.

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