DrawTextEncodingLocaleSettings

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DrawTextEncodingLocaleSettings

If you are just concerned with drawing “standard” ASCII text with the
Screen(‘DrawText’, window, text); command, i.e. text that only contains
“standard” latin characters, e.g., abcdef….ABCDEF…. and numbers
01234567890 and a few punctuation marks and symbols like .,!?#@$%& etc.
then there’s nothing you’d need to do. Screen(‘DrawText’) and
DrawFormattedText() will process these just fine.

If you want to draw “native” unicode text strings conforming to UTF-16
encoding with characters or code points in the BMP (Basic multilingual
plane), you can simply convert your string of unicode code points into a
vector of doubles, ie., pass it as a vector of numbers of class double(),
e.g., text = [1424, 1425, 1426] for the first three characters of the
hebrew alphabet.

Direct drawing of unicode text characters outside the BMP is possible in
the same way the default textrenderer if you’ve installed the neccessary
software as described in “help DrawTextPlugin”. In that case, the unicode
code points may have values greater than 65535, ie., they are processed
internally as UTF-32 / UCS-4 characters - Each single number represents
exactly one character and the numbers can be codepoints from any Unicode
plane.

The legacy OS/X text renderer and MS-Windows text renderer, which are
used if you select Screen(‘Preference’, ‘TextRenderer’, 0) or if the
standard renderer does not work, only support UTF-16 / UCS-2 encoding.
Therefore, characters outside of the BMP must be represented by pairs of
codepoints, each with a value between 0 and 65535 - Two consecutive
values in your double vector will represent one character from outside
the BMP.

You can also draw non-ASCII character strings encoded into some
single-byte encoding scheme, multibyte encoding scheme or unicode
characters that are not encoded as doubles but as a sequence of UTF-8
encoded bytes. To do so, first you have to tell Screen() the encoding
scheme of the character string by a call to
Screen(‘Preference’,’TextEncodingLoale’, newloc); newloc is the name of
the text encoding scheme to use. Example names for valid locales could be
‘en_US.ISO8859-1’ for single-byte ISO8859-1 “Latin-1” encoding, or
‘UTF-8’ for UTF-8 encoded unicode text, or ‘C’ for default C language
character encoding. Passing an empty string ‘’ will reset the setting to
the system default of your operating system. The function returns the
previous setting. On OS/X and Linux you can type “locale -a” in a
terminal window to list all supported settings. For MS-Windows you can
find supported codepages under this URL:
http://msdn.microsoft.com/en-us/library/dd317756%28VS.85%29.aspx e.g.,
setting a locale of ‘.1252’ would select MS-Windows codepage 1252, aka
‘windows-1252’. A setting of ‘UTF-8’ for UTF-8 encoded unicode should
always work. The set of other supported encodings is highly operating
system dependent.

After you’ve told Screen the encoding to use, you can pass strings to
Screen(‘DrawText’). If you want to make sure that Matlab or Octave don’t
tamper in unexpected or uncontrollable ways with your string, you can
pass the string as a uint8 vector. Passing the string as uint8 vector is
recommended in most cases. Different versions of Matlab and Octave store
and process regular char() character strings in different ways on
different operating systems which can often lead to unexpected results.
On some setups you will be able to directly pass regular text strings,
but this is not guaranteed to be portable across different computer
systems, Matlab or Octave versions.

If you get unexpected results for given text strings you can call
Screen(‘Preference’,’Verbosity’, 10); before a drawtext operation. The
function will then print the passed string as a sequence of numbers after
conversion into unicode format. This allows to check what kind of unicode
characters were generated.

Assuming Screen(‘DrawText’) managed to receive your final (unicode) text
string correctly, you’ll also have to make sure that a font is selected
that supports the characters in your string. E.g., not all fonts support
hebrew characters. Use Screen(‘TextFont’, window, fontName); to select a
proper font fontName. How to find such a font is operating system
specific. The default text renderer allows to select fonts by properties
instead of names as well, e.g., it allows to select a font that supports
a requested language: Screen(‘Textfont’, window, ‘-:lang=he’); would
select a font that supports hebrew. Screen(‘Textfont’, window,
‘-:lang=ja’); would select a font that supports japanese script. See
some more examples in the code of DrawHighQualityUnicodeTextDemo.m.

If you type DrawTextEncodingLocaleSettings to run this script, you may
see some hebrew characters rendered if your systems fonts and text
renderers do support this. This code also acts as a sample on how to pass
UTF-8 unicode strings to ‘DrawText’.

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Psychtoolbox/PsychDocumentation/DrawTextEncodingLocaleSettings.m