[newX,newY,textHeight]=Screen(‘DrawText’, windowPtr, text [,x] [,y] [,color] [,backgroundColor] [,yPositionIsBaseline] [,swapTextDirection]);
Draw text. “text” may include Unicode characters (e.g. Chinese).
A standard Matlab/Octave char()acter text string is interpreted according to
Screen’s current character encoding setting. By default this is the “system
default locale”, as selected in the language settings of your user account. You
can change the encoding anytime via a call to Screen(‘Preference’,
‘TextEncodingLocale’, newencoding); E.g., for UTF-8 multibyte character encoding
you’d call Screen(‘Preference’,’TextEncodingLocale’,’UTF-8’);
If you have a non-ASCII text string and want to make sure that Matlab or Octave
doesn’t meddle with your string, convert it into a uint8() datatype before
passing to this function.
If you want to pass a string which contains unicode characters directly, convert
the text to a double matrix, e.g., mytext = double(myunicodetext); then pass the
double matrix to this function. Screen will interpret all double numbers
directly as unicode code points.
Unicode text drawing is supported on all operating systems if you select the
default high quality text renderer. Of course you also have to select a text
font which contains the unicode character sets you want to draw - not all fonts
contain all unicode characters.
The following optional parameters allow to control location and color of the
“x” “y” defines the text pen start location. Default is the location of the pen
from previous draw text commands, or (0,0) at startup. “color” is the CLUT index
(scalar or [r g b] triplet or [r g b a] quadruple) for drawing the text; startup
default produces black.
“backgroundColor” is the color of the background area behind the text. By
default, text is drawn transparent in front of whatever image content is stored
in the window. You need to set an explicit backgroundColor and possibly enable
user defined alpha-blending with Screen(‘Preference’, ‘TextAlphaBlending’, 1);
and Screen(‘Blendfunction’, …) to make use of text background drawing.
Appearance of the background + text may be different accross different operating
systems and text renderers, or it may not be supported at all, so this is not a
feature to rely on.
“yPositionIsBaseline” If specified, will override the global preference setting
for text positioning: It defaults to off. If it is set to 1, then the “y” pen
start location defines the base line of drawn text, otherwise it defines the top
of the drawn text. Old PTB’s had a behaviour equivalent to setting 1,
unfortunately this behaviour wasn’t replicated in early versions of
Psychtoolbox-3, so now we stick to the new behaviour by default.
“swapTextDirection” If specified and set to 1, then the direction of the text is
swapped from the default left-to-right to the swapped right-to-left direction,
e.g., to handle scripts with right-to-left writing order like hebrew.
“newX, newY” optionally return the final pen location.
“textHeight” optionally return height of current text string. May return zero if
this is not supported by the current text renderer.
Btw.: Screen(‘Preference’, …); provides a couple of interesting text
preference settings that affect text drawing, e.g., setting alpha blending and
Selectable text renderers: The Screen(‘Preference’, ‘TextRenderer’, Type);
command allows to select among different text rendering engines with different
Type 0 is the legacy OS specific text renderer: On Linux this is implemented as
a fast, but low quality OpenGL display list renderer without any support for
unicode or text anti-aliasing. On MS-Windows, this is currently a GDI based
renderer. On OSX this currently selects Apples CoreText text renderer, which is
slow but does support anti-aliasing, unicode and other features. Normally you
really don’t want to use the type 0 legacy renderer. It is provided for
backwards compatibility to old experiment scripts and may need to get removed
completely in future versions of Psychtoolbox due to circumstances out of our
Type 1 is the high quality renderer: It supports unicode, anti-aliasing, and
many other interesting features. This is a renderer loaded from an external
plugin, and based on FTGL for fast high quality text drawing with OpenGL.
This function doesn’t provide support for text layout. Use the higher level
DrawFormattedText() function if you need basic support for text layout, e.g,
centered text output, line wrapping etc.