drawFixationCross.m

function drawFixationCross(windowPtr, fixCrossSize, fixCrossWidth, ...
    centerCoords, color)

% DRAWFIXATIONCROSS - Draw fixation cross on Psychtoolbox window
%    This MATLAB function draws a fixation cross at a specified location on
%    a specified Psychtoolbox (PTB) window.
%
%    INPUT ARGUMENTS
%      windowPtr (int) - Index of the PTB window that the fixation cross
%                        ought to be drawn on.
%
%      fixCrossSize (int) - Length of the bars that make up the fixation
%                           cross in pixels.  Must be positive.
%
%      fixCrossWidth (int) - Thickness of the bars that make up the
%                            fixation cross in pixels.  Must be positive.
%
%      centerCoords (int) - Coordinates of the center of the fixation cross
%                           in pixels.
%
%      color (double) - 1 x 3 vector representing a color in RGB color
%                       space.  Can also be a single value (grayscale).
%                       Color range is assumed to be the normalized
%                       floating point number range 0.0 - 1.0.  Defaults to
%                       0 (i.e., black) if not specified.
%
%    ASSUMPTIONS & LIMITATIONS
%      Psychtoolbox (<http://psychtoolbox.org>) needs to be installed.
%      For system requirements regarding the use of Psychtoolbox, please
%      check <http://psychtoolbox.org/requirements.html>.

% Copyright (c) 2023 Marvin Theiss
% 
% Permission is hereby granted, free of charge, to any person obtaining a copy
% of this software and associated documentation files (the "Software"), to deal
% in the Software without restriction, including without limitation the rights
% to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
% copies of the Software, and to permit persons to whom the Software is
% furnished to do so, subject to the following conditions:
% 
% The above copyright notice and this permission notice shall be included in all
% copies or substantial portions of the Software.
% 
% THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
% IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
% FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
% AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
% LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
% OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
% SOFTWARE.

arguments
    windowPtr (1, 1) double {mustBeInteger}
    fixCrossSize (1, 1) double {mustBeInteger, mustBePositive}
    fixCrossWidth (1, 1) double {mustBeInteger, mustBePositive}
    centerCoords (1, 2) double {mustBeInteger, mustBePositive}
    color (1, 3) double { ...
        mustBeGreaterThanOrEqual(color, 0), ...
        mustBeLessThanOrEqual(color, 1) ...
        } = 0
end

% Compute size of a single arm of the fixation cross
singleArmSize = floor(fixCrossSize ./ 2);  % in pixels

% Set up coordinates
xCoords = [-singleArmSize, singleArmSize, 0, 0];
yCoords = [0, 0, -singleArmSize, singleArmSize];
allCoords = [xCoords; yCoords];

% Draw fixation cross
Screen('DrawLines', windowPtr, ...
    allCoords, fixCrossWidth, color, centerCoords);

end