# How to draw an arrow or triangle

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Brett on 14 Nov 2012
Answered: Sanjay Manohar on 14 Feb 2017
Hello Matlab community, I am trying to draw an arrow. I am using Psychtoolbox and there doesn't seem to be a specific command for arrows or triangles. I know how to draw a line:
line = [X-3,Y-40,X+3,Y+40];
Screen('FillRect',window,[200,200,200], line');
So if someone knows the code to draw a triangle I can merge it with the code for a line to draw an arrow. Any help would be greatly appreciated.
Thanks, Brett
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### Answers (3)

Sanjay Manohar on 14 Feb 2017
This is not a MATLAB question. But for completeness, the answer should be
% create a triangle
head = [ 100, 100 ]; % coordinates of head
width = 10; % width of arrow head
points = [ head-[width,0] % left corner
head+[width,0] % right corner
head+[0,width] ]; % vertex
Screen('FillPoly', window,[200,200,200], points);
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Image Analyst on 14 Nov 2012
Are you aware of the annotation() function?
annotation('line',x,y)
annotation('arrow',x,y)
annotation('doublearrow',x,y)
annotation('textarrow',x,y)
annotation('textbox',[x y w h])
annotation('ellipse',[x y w h])
annotation('rectangle',[x y w h])
annotation(figure_handle,...)
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sina farahi on 9 Apr 2014
annotation('arrow',x,y) doesn't work
Image Analyst on 9 Apr 2014
Edited: Image Analyst on 9 Apr 2014
At all? Or just with some figure created by the Psychtoolbox (which is not a Mathworks product and I don't have)? Does this draw an arrow for you:
plot(1:10, 'LineWidth', 2);
grid on;
annotation('arrow', [.21, .5], [.85, .5], 'LineWidth', 2);

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sina farahi on 9 Apr 2014
usage: Arrow(dot,vector); note: This function draw an arrow (head lines have pi/6 angle and the length of l/5) example: Arrow([10;11;12],[0.2;20;25]);
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