How to create randomly distributed triangles

I need to create a moving visual display consisting of 500 randomly distributed white triangles (3.4 × 3.4 × 3 cm) on a black background. The frame rate of the visual display needs to be 60 Hz, triangles move in fore-aft direction. Could you please help me figure this out? Thank you.

[Rik]

What steps did you try yourself?

Also, 60 hertz is quite a lot for live generation. Matlab is not a game engine, so this will require a powerful computer. If you write a file you will have a better chance to reach 60 fps.

[Ron]

w=10; %width of triangle
ar=0.866; % Aspect ratio for equilateral triangle
h=ar*w;%height of triangle
x=[0 w w/2];%x coordinates of vertices
y=[0 0 h];%y coordinates of vertices
patch(x,y,'white') %plotting triangle in white color
set(gca,'Color','k','xticklabel',[],'yticklabel',[])%setting background black and removing labels
daspect([1 1 1]);%equal data unit length along x and y axis
xlim([-5 15])
ylim([-5 15])

This code creates one triangle. How can I create randomly distributed multiple triangles?

[Matt J]

Are the triangle positions supposed to be completely random in each frame, or does there need to appear to be gradual frame-to-frame motion? If so, what kind of motion? Could we just rotate the image like a merry-go-round?

[Ron]

Thanks for your attention. Triangles needs to be randomly spaced, frame rate of visual display needs to be 60 Hz and then the triangles need to rotate 0.8 degrees about a horizontal axis at 0.2 Hz.

w = 3 ;
ar=0.866; % Aspect ratio for equilateral triangle
h=ar*w;%height of triangle
 
x=[0 w w/2];%x coordinates of vertices
y=[0 0 h];%y coordinates of vertices
p= patch(x,y,'white'); %plotting triangle in white color
set(gca,'Color','k','xticklabel',[],'yticklabel',[])%setting background black and removing labels
daspect([1 1 1]);%equal data unit length along x and y axis
xlim([-5 15])
ylim([-5 15])
 
pr = rotate(p, 0.8,[ 0 0 1], [0 0 0]);

I used rotate to rotate the triangle about x axis, but it didn't rotate.

[Rik]

That is an almost imperceptible speed. Why do you want 60 Hz if your actual movement is 0.2 Hz?

[Ron]

https://www.youtube.com/watch?v=qZLO2EE_oKE

Visual movement in fore-aft direction as shown in this video is the reason for the 60 Hz frame rate. The 0.8 degree rotation at 0.2 Hz is superimposed on top of it.

[Rik]

If you want to create something like that I would still encourage you to produce a video, instead of creating the video in real time. The code in my answer will run at 200fps, but that will quickly drop when you put more graphics object in a figure. I also have a reasonly powerful computer, so you would have to verify the performance of your target computer.

[Ron]

Can I use matlab to produce the video? What other program would you recommend? I will need to start and stop the video at specific times in sync with start times of another device.

[Rik]

You can write videos with Matlab. I have never done that before, so I would have to do the same as you: google 'write video Matlab'. You can produce each frame as an image and write it to a video file.

Syncing with an external device might be tricky though. That depends mostly on how that sync should work.

[Ron]

Thank you, Rik. I'll look into making a video. And then use a DAQ to connect with other device.

Answer 1

[Rik]

Slightly editing your code gets me to a max framerate of just under 200. Results will vary for different systems.

w = 3 ;
ar=0.866; % Aspect ratio for equilateral triangle
h=ar*w;%height of triangle
p=[];origins=cell(1,10);
figure(1),clf(1)
for k=1:10
    x=[0 w w/2];%x coordinates of vertices
    y=[0 0 h];%y coordinates of vertices
    x=x+15*rand-5;y=y+15*rand-5;%add random
    p(k)= patch(x,y,'white'); %#ok<SAGROW> plotting triangle in white color
    origins{k}=[mean(x) mean(y) 0];%store explicitly to prevent having to retrieve it from an object
end
set(gca,'Color','k','xticklabel',[],'yticklabel',[])%setting background black and removing labels
daspect([1 1 1]);%equal data unit length along x and y axis
xlim([-5 15]),ylim([-5 15])

rotation_per_frame_in_deg=0.8;
target_fps=60;
frametime=1/target_fps;
h_tic=tic;
for n=1:60%do 60 frames
    tic
    for k=1:numel(p)
        rotate(p(k),[0 0 1],rotation_per_frame_in_deg,origins{k})
    end
    drawnow
    pause(frametime-toc)%comment this line to see the max framerate
end
t=toc(h_tic);
fprintf('the fps was %.1f Hz\n',n/t)

[Ron]

Thank you. the frame rate is to create illusion of continuous movement, the 0.8 degrees st 0.2 Hz is to create illusion of rotation on top of the movement. The visual display needs to continuously be looping for 3 minutes.

[Ron]

Thanks so much for your help with the code above! Specially that I can appreciate the frame rate change.

[Rik]

Why did you remove part of your question? Now my answer is much less useful to others with a similar problem.

Luckily there is a copy of this thread on the Wayback Machine, so I could undo your edits.