Create random parallel black lines in a white box until tis filled

Hi everyone I am creating a white box and creating an initial black line that goes through the box and then i am trying to create random lines parallel to the initial one up until the whole box is filled.

My code is this one:

clc; clear; close;

% Define the size of the square
squareSize = 100;

% Create a square with white background
square = ones(squareSize, squareSize);

% Calculate the middle row of the square
middleRow = round(squareSize/2);

% Define the initial line thickness
lineThickness = 1;

% Draw a black line in the middle row of the square with the given thickness
square(max(1, middleRow-floor(lineThickness/2)):min(squareSize, middleRow+ceil(lineThickness/2)), :) = 0;

% Display the square with the black line
%imshow(square);

% Save the image with the initial line thickness
imwrite(square, 'line_thicknessrandom_1.png');

% Draw random lines parallel to the initial line
i = 1;
while any(square(:)==1)
    % Generate random y-coordinate for the line
    randRow = randi([1, squareSize]);
    
    % Check if the random line overlaps with any existing line
    while any(square(max(1, randRow-floor(lineThickness/2)):min(squareSize, randRow+ceil(lineThickness/2)), :)==0)
        % Generate new random y-coordinate for the line
        randRow = randi([1, squareSize]);
    end
    
    % Draw a black line at the non-overlapping random y-coordinate with the same thickness as the initial line
    square(max(1, randRow-floor(lineThickness/2)):min(squareSize, randRow+ceil(lineThickness/2)), :) = 0;

    % Save the image with the updated line thickness and random lines
    filename = sprintf('line_thicknessrandom_%d.png', i+1);
    imwrite(square, filename);
    
    % Increment the counter variable
    i = i + 1;
end

and while it does create a lot o parallel lines it stops at a certain point before the whole box is filled.

Does anyone know how to fix this?

Answer 1

[DGM]

The lines you're drawing are 2px wide, so the inner loop will never be satisfied once the only remaining stripes are 1px wide. You'll have to decide what you want to do, since filling those remaining lines strictly violates the conditions your code has in place for line placement.

[lena kappa]

Thank you for your quick response! Why are they 2pxl wide?

[DGM]

That's just the way the math works out. Your line will always be 1px wider than specified. You could address this ...

lineThickness = (1:3).';

ltk = (lineThickness-1)/2; % precalculate with offset
[-floor(ltk) ceil(ltk)] % the offsets

ans = 3×2

0 0 0 1 -1 1

... but you're still going to have problems for any case where lineThickness is >1. There's no guarantee that you won't have leftover rows that are narrower than the specified linewidth.

If the goal is to draw random (horizontal) lines without overlap, then this may simplify if you can accept that the lines are uniformly spaced. At that point, it's a simple permutation problem, and requires no tests.

Consider the example:

% these must be integers (obviously)
squaresize = 100;
linewidth = 3;

% calculate some things
numlines = ceil(squaresize/linewidth);
lineorder = randperm(numlines);

outpict = true(squaresize); % preallocate
for k = 1:numlines
    % calculate row subscripts for this line
    thisline = lineorder(k);
    row1 = (thisline-1)*linewidth+1;
    row2 = min(row1+linewidth-1,squaresize);
    
    % assign rows
    outpict(row1:row2,:) = false;
    
    % i'm not going to write to disk
    % so just show it instead
    imshow(outpict)
    pause(0.1)
end

There are other ways to do the same, but this is just one idea.

[lena kappa]

@DGM thank you!

[lena kappa]

Thank you!