How to generate rectangles based on coordinates in a randomized matrix?

So I have a matrix. Currently it looks like this:

S.matrix =

     2    78    46
     1   148   148
     3   431   431
     1   224   224
     1   595   595
     3    58    58
     1   160   160
     1   244   244
     1   410   410
     1   526   526

Now I have code that makes this matrix random, meaning the numbers are all random (as long as they are between 1 and 640) as well as the size. The amount of columns stay the same, but the rows are not set. My current code has it that as longs as a certain condition is fulfilled, a new row to the matrix is added, hence the ambigous size. For the sake of debugging, I set the condition to a certain point such that the code will always produce a 3x10 matrix.

        if S.matrix(:,1) == 1

            S.blasterEM = rectangle("Position",[S.matrix(:,2) S.matrix(:,3) 5 10]);
            S.blasterEM.FaceColor = [1 0 0];
            S.blasterEM.EdgeColor = NA;
            
        elseif S.matrix(:,1) == 2
        
            S.sniperEM = rectangle("Position",[S.matrix(:,2) S.matrix(:,3) 5 15]);
            S.sniperEM.FaceColor = [1 0 1];
            S.sniperEM.EdgeColor = NA;

        elseif S.matrix(:,1) == 3
            
            S.chaserEM = rectangle("Position",[S.matrix(:,2) S.matrix(:,3) 5 20]);
            S.chaserEM.FaceColor = [0 1 0];
            S.chaserEM.EdgeColor = NA;

        end

This code runs if statements depending on the first column and is supposed to produce rectangels according to the corresponding row. For example, S.matrix(1,1) will produce a specific type of rectangle at coordinates (78, 46). However, not only are the rectangles not showing up in the figure, I believe the rectangles aren't being produced at all. Is there a way I can make the if statements more precise such that any time the column at S.matrix(:,1) fulfills the parameters of the if statement, it will produce a rectangle at the corresponding coordinates? I also want to be able to make it so that the it will produce rectangles no matter the N of a 3xN matrix.

Any help is appreciated. Sorry if my problems seems a bit confusing to understand. Comment any misunderstandings, and I will do my best to answer.

Answer 1

[Voss]

S.matrix(:,1) is a vector, so S.matrix(:,1) == 1 is a vector (of class logical) the same size as S.matrix(:,1). When that vector is used as a condition in an if statement, it's considered true (i.e., the code inside if block executes) only if all of that vector's elements are true.

In this case S.matrix(:,1) is not all 1's and it's not all 2's and it's not all 3's, so none of those if/elseif conditions are considered true, so no rectangles are created.

There are different ways to create those rectangles and store them. Here's one way, in which S.blasterEM, S.sniperEM and S.chaserEM are all arrays of rectangles (because in general there can be more than one rectangle of each type). The logic here is the same as yours, but within a for loop where each element of S.matrix(:,1) is checked separately and a new rectangle of the appropriate type is created and added to the appropriate array of rectangles.

(I assumed NA meant "none", since it wasn't defined.)

S.matrix = [
     2    78    46
     1   148   148
     3   431   431
     1   224   224
     1   595   595
     3    58    58
     1   160   160
     1   244   244
     1   410   410
     1   526   526
    ];

S.blasterEM = [];
S.sniperEM = [];
S.chaserEM = [];

for ii = 1:size(S.matrix,1)
    if S.matrix(ii,1) == 1
        S.blasterEM(end+1) = rectangle( ...
            "Position",[S.matrix(ii,2) S.matrix(ii,3) 5 10], ...
            "FaceColor",[1 0 0], ...
            "EdgeColor","none"); % specify the properties when the rectangle is created ...
    elseif S.matrix(ii,1) == 2
        S.sniperEM(end+1) = rectangle("Position",[S.matrix(ii,2) S.matrix(ii,3) 5 15]);
        set(S.sniperEM(end),'FaceColor',[1 0 1]); % ... or set() the properties afterward
        set(S.sniperEM(end),'EdgeColor',"none");
    elseif S.matrix(ii,1) == 3
        S.chaserEM(end+1) = rectangle( ...
            "Position",[S.matrix(ii,2) S.matrix(ii,3) 5 20], ...
            "FaceColor",[0 1 0], ...
            "EdgeColor","none");
    end
end

[NinaCodes]

Thank you so much!

[Voss]

You're welcome!

[NinaCodes]

I have another question if you don't mind. Specifically for the S.chaser object, is there a way where I can code the S.matrix(ii,2) and S.matrix(ii, 3) of each rectangle under S.chaser such that it will move 3 points according to an object that changes position over time? I have a ship object which I will put the code below that changes position according to key press, and I want the chaser object, well, chase after the ship.

I thought of finding the equation of a line between the center of the ship object and the coordinates of the rectangle so that S.matrix(ii,2) and S.matrix(ii, 3) of each rectangle under S.chaser will move to 3 pixels in the direction of the line, then I remembered that S.chaser contains more than one rectangle so it would be hard to code that.

%creates parameters for ship
xCenter = 320;
yCenter = 320;
radius = 20;

function h = circle(xCenter,yCenter,radius)
        % function that makes the ship
        hold on
        th = 0:pi/50:2*pi;
        xunit = radius * cos(th) + xCenter;
        yunit = radius * sin(th) + yCenter;
        h = plot(xunit, yunit, "Color", 'c', 'LineWidth', 2);
        hold off
end

function [] = fig_kpfcn(~,E)
    %function that corresponds to key press
    if j == 1
        switch E.Key
            case 'rightarrow'
                set(S.ship,'XData',get(S.ship,'XData')+3);
            case 'leftarrow'
                set(S.ship,'XData',get(S.ship,'XData')-3);
            case 'uparrow'
                set(S.ship,'YData',get(S.ship,'YData')+3);
            case 'downarrow'
                set(S.ship,'YData',get(S.ship,'YData')-3);
        end
        makePoints()
    end
end

[Voss]

Let me make sure I understand how it should work. Each time the ship moves (due to a key press), all the rectangles in S.chaser should move 3 units closer to the new center of the ship?

[NinaCodes]

Correct!

[Voss]

OK. Thinking about it a bit more, the distance should be based on the lower-left corner of the rectangle? I mean that's the value in S.matrix(:,[2 3]). Maybe it would make more sense if it's the distance from ship center to the nearest corner of each rectangle, or maybe distance to the rectangle center (this would probably be easiest).

And what should happen if a rectangle is already less than 3 units away from the ship center? Should it move closer by a smaller amount, say a certain fraction of its distance away? Or maybe it should not move at all?

[NinaCodes]

The rectangle center sounds good since it'll be easier.

If the rectangle is less than 3 units away, then the rectangle is deleted (kami kaze). This is because the chaser has caught up to the ship and the ship loses 1 out of the three lives it has. I also think instead of moving three pixels, it'll move 4 so the chaser has a chance to catch up with the ship.

[Voss]

Here's a working program that does the ship and chaser movement. You can run it on its own, and also take the parts you need (particularly from fig_kpfcn) into your own program. I had to make assumptions about the structure of the program (here I'm using nested functions, for instance), so you may have to make appropriate modifications to the parts you use.

Note that this updates the chasers' rectangles directly, rather than updating S.matrix, but you can modify it to update S.matrix and then update the rectangles from that, if that's necessary.

function main_game()

%creates parameters for ship
xCenter = 320;
yCenter = 320;
radius = 20;

j = 1;

figure('KeyPressFcn',@fig_kpfcn);

S = struct( ...
    'ship',circle(xCenter,yCenter,radius));

S.matrix = [
     2    78    46
     1   148   148
     3   431   431
     1   224   224
     1   595   595
     3    58    58
     1   160   160
     1   244   244
     1   410   410
     1   526   526
    ];

S.blasterEM = [];
S.sniperEM = [];
S.chaserEM = [];

for ii = 1:size(S.matrix,1)
    if S.matrix(ii,1) == 1
        S.blasterEM(end+1) = rectangle( ...
            'Position',[S.matrix(ii,2) S.matrix(ii,3) 5 10], ...
            'FaceColor',[1 0 0], ...
            'EdgeColor','none');
    elseif S.matrix(ii,1) == 2
        S.sniperEM(end+1) = rectangle( ...
            'Position',[S.matrix(ii,2) S.matrix(ii,3) 5 15], ...
            'FaceColor',[1 0 1], ...
            'EdgeColor','none');
    elseif S.matrix(ii,1) == 3
        S.chaserEM(end+1) = rectangle( ...
            'Position',[S.matrix(ii,2) S.matrix(ii,3) 5 20], ...
            'FaceColor',[0 1 0], ...
            'EdgeColor','none');
    end
end



function h = circle(xCenter,yCenter,radius)
        % function that makes the ship
        hold on
        th = 0:pi/50:2*pi;
        xunit = radius * cos(th) + xCenter;
        yunit = radius * sin(th) + yCenter;
        h = plot(xunit, yunit, 'Color', 'c', 'LineWidth', 2);
        hold off
end



function [] = fig_kpfcn(~,E)
    %function that corresponds to key press
    if j == 1
        switch E.Key
            case 'rightarrow'
                set(S.ship,'XData',get(S.ship,'XData')+3);
                xCenter = xCenter+3;
            case 'leftarrow'
                set(S.ship,'XData',get(S.ship,'XData')-3);
                xCenter = xCenter-3;
            case 'uparrow'
                set(S.ship,'YData',get(S.ship,'YData')+3);
                yCenter = yCenter+3;
            case 'downarrow'
                set(S.ship,'YData',get(S.ship,'YData')-3);
                yCenter = yCenter-3;
            otherwise
                % return if another key was pressed, so that the code 
                % below doesn't run if the ship didn't move
                return
        end
        
%         makePoints() % not sure what this does or where it should be 
                     % relative to the rest of the code I'm putting here
        
        if ~isempty(S.chaserEM)
            
            % get chasers' centers:
            pos = get(S.chaserEM,'Position');
            if iscell(pos)
                pos = vertcat(pos{:});
            end
            rec_centers = pos(:,[1 2])+pos(:,[3 4])/2;
            
            % calculate vectors between ship_center and rec_centers:
            v_centers = rec_centers-[xCenter yCenter];
            % calculate distances between ship_center and rec_centers:
            d_centers = sqrt(sum(v_centers.^2,2));
            
            % move chasers closer to ship center by 4 units:
            % first set the new distances (use max(0,__) so the chasers
            % don't cross the ship center)
            d_centers = max(0,d_centers-4);
            % get the direction of each chaser from the ship
            v_angles = atan2(v_centers(:,2),v_centers(:,1));
            % get the new chaser centers by calculating the points along
            % those directions, d_centers away from the ship
            v_centers = [xCenter yCenter]+d_centers.*[cos(v_angles) sin(v_angles)];
            % set the lower-left corners of the chasers
            pos(:,[1 2]) = v_centers-pos(:,[3 4])/2;
            % update the chaser Positions
            for ii = 1:numel(S.chaserEM)
                set(S.chaserEM(ii),'Position',pos(ii,:));
            end
            
            % handle rec_centers less than 3 units of [xCenter yCenter]:
            idx = d_centers < 3;
            if any(idx)
                % delete the successful kamikaze chasers
                delete(S.chaserEM(idx));
                % remove the dead rectangles from the array
                S.chaserEM(idx) = [];
                % decrement the ship's lives by 1, or by nnz(idx) if each kamikaze 
                % chaser that gets within 3 units contributes a 1-life decrement:
                % TBD (I don't know what variable in your code this would be)
                % if ship has no remaining lives, do something special I assume
            end
            
        end
        
    end
    
end

end