Workaround for matrix dimension error

Hello guys,

I already asked a few questions about my LED-Matrix project and it is getting closer to its final state.

So when implementing my mousemode I wanted to switch between several figures which I "draw" in an array around the Mouseposition.

unction Transmit = MouseFigure(MousePos,Transmit,handles)
global click
%click = 3;
brtn = get(handles.slider1, 'Value');
switch click
    case 1 %%Kreuz%%
        Transmit(MousePos(1),MousePos(2)) = 255*brtn;
        Transmit(MousePos(1)+1,MousePos(2)) = 255*brtn;
        if MousePos(1) > 1
            Transmit(MousePos(1)-1,MousePos(2)) = 255*brtn;
        end
        if MousePos(2) > 1
            Transmit(MousePos(1),MousePos(2)-1) = 255*brtn;
        end
        Transmit(MousePos(1),MousePos(2)+1) = 255*brtn;
    case 2 %%Rechteck 3x3 Pixel%%
        for i = 1:3
            if MousePos(1) < 2
                i = 2;
            end
            Transmit(MousePos(1)-2+i,MousePos(2)+1) = 255*brtn;
            Transmit(MousePos(1)-2+i,MousePos(2)) = 255*brtn;
            Transmit(MousePos(1)-2+i,MousePos(2)+1) = 255*brtn;
            Transmit(MousePos(1)-2+i,MousePos(2)) = 255*brtn;
            if MousePos(2) > 2
                Transmit(MousePos(1)-2+i,MousePos(2)-1) = 255*brtn;
            end
        end
    case 3 %%Kreis 3,5,5,5,3%%
        for i = 1:5
            if MousePos(1) > 3
                Transmit(MousePos(1)-3+i,MousePos(2)+1) = 255*brtn;
                Transmit(MousePos(1)-3+i,MousePos(2)) = 255*brtn;
            end
            if MousePos(2) > 1
                Transmit(MousePos(1)-3+i,MousePos(2)-1) = 255*brtn;
            end
            if MousePos(1) > 4
                Transmit(MousePos(1)-4+i,MousePos(2)+2) = 255*brtn;
                if MousePos(2) > 2
                    Transmit(MousePos(1)-4+i,MousePos(2)-2) = 255*brtn;
                end
            end
        end
end
Transmit = Transmit([1:32],[1:32]);
Transmit = rot90(Transmit,1);
Transmit = reshape(Transmit,[1,1024]);

But when doing this in my method as you can see there are always those if-cases for the outer line of the drawn figure to avoid matrix dimension errors. Now my question is, is there a smarter workaround for this error or even for "drawing" those figures in my array?

Answer 1

[Jan]

Hints:

Avoid repeated code. Prefer:

brtn = 255 * get(handles.slider1, 'Value');

instead of writing 255*brtn whenever brtn is used. Typing "MousePos(1)" repeatedly is a source of typos also. What about:

x = MousePos(1);
y = MousePos(2);

The standard method for comments is to start with a % and a space. "%%Kreuz%%" looks fancy, but not Matlab'ish.

X(1:32) is faster than X([1:32]). The reason is not documented, but it seems like Matlab checks the limits for 1 and 32 only, while in the latter case the vector 1:32 is created explicitly and the limits are checked for each element. Remember that [] is the Matlab operator for concatenation, so there is no need to concat teh vector 1:32 with nothing else.

The actual question: Replace e.g.:

        Transmit(MousePos(1),MousePos(2)) = 255*brtn;
        Transmit(MousePos(1)+1,MousePos(2)) = 255*brtn;
        if MousePos(1) > 1
            Transmit(MousePos(1)-1,MousePos(2)) = 255*brtn;
        end
        if MousePos(2) > 1
            Transmit(MousePos(1),MousePos(2)-1) = 255*brtn;
        end
        Transmit(MousePos(1),MousePos(2)+1) = 255*brtn;

by

        xi = max( 1, x - 1);
        xf = min(32, x + 1);
        yi = max( 1, y - 1);
        yf = min(32, y + 1);
        Transmit(xi:xf, y)     = brtn;
        Transmit(x,     yi:yf) = brtn;

An alternative approach:

T = zeros(40, 40);
x = MousePos(1) + 4;
y = MousePos(2) + 4;
... % Insert the values without considering the limits
Transmit = T(5:36, 5:36);
...

So you draw without considering the limits and crop out the visible area afterwards. I'd prefer this, because it is much easier to expand for other objects.

[Benedikt Schwarz]

T = zeros(40, 40);
x = MousePos(1) + 4;
y = MousePos(2) + 4;
... % Insert the values without considering the limits
Transmit = T(5:36, 5:36);
...

Awesome I never thought of this approach... Thanks a lot, looks way better now!