CODEWITHSUNDEEP
matlabplotmatlab-figurepatchrectangles
pelt
pelt

Reputation: 113

Filling in rectangles drawn with the patch function

I am wanting to draw rectangles on a figure that I am creating. I also would like to be able to fill that rectangle with a transparent color. So I am using 'Patch' instead of 'Rectangle' which will allow me to do so.

I am able to get the rectangles in the location and the size that I want, but I cannot seem to get the filling in with transparency the way that I think it should work?

In the documentation, it is of the form:

p=patch(X,Y, 'c')

When I enter this in, it never takes into account that Color denoted by 'c'/cyan, and will just plot a standard black rectangle. However, I can set the color with the dot index notation of:

p.EdgeColor='c';

My actual script is different as the X's and Y's are variable, but I am attaching a very simple script here to simulate my issue of my vectorized plotting issue. It simply creates Xs vertices at every 10th location, with a width of 2, and a height of 10.

Am I misusing the patch function to get it to fill with a transparent color with FaceAlpha?

clear all;

% Generate some simple X value data, where each X is the X value starting from the
% lower left of the rectangle, in a clockwise fashion around the edges of
% rectangle.
X1(:,1) = 0:10:100;
X2(:,1) = 0:10:100;
X3(:,1) = X1+2;
X4(:,1) = X1+2;

% Rotate the X vectors into rows. 
X1 = X1(:)';   
X2 = X2(:)';
X3 = X3(:)';    
X4 = X4(:)';

% Here I am stacking each X on top of each other, and padding the bottom
% row with NaNs.  Adding a similar Y set of values, which will simply be a
% height of 0-10
X =[X1; X2; X3; X4; 
    nan(size(X1))   ];
Y =[zeros(size(X1));        10+zeros(size(X2)); ...
    10+zeros(size(X3));     zeros(size(X4));     
    nan(size(X1))  ];


% Rotate vectors so that the last value in the X/Y coordinates is a NaN,
% and Matlab will ignore and plot the next value
X=X(:);
Y=Y(:);

% This Plots the outline of the rectangles I am looking for, with a width
% of 2, height of 10, starting at each 10th value of X
p=patch( X ,Y,'c');
p.EdgeColor = 'b';  %Comment this out to see that the Patch function is not working?
p.FaceColor = 'blue';
p.FaceAlpha = 0.5;

% But for some reason it is not FILLING in the rectangles/patches I have
% drawn?

Upvotes: 2

Views: 588

Answers (2)

EBH
EBH

Reputation: 10440

Your problem is not with the color but with X and Y, they should be a 4-by-n matrix. Here is a way to do this:

x = [0:10:100; (0:10:100)+2];
X = reshape(repelem(x(:),2),4,[]);
Y = repmat([0; 10; 10; 0],1,size(X,2));
p = patch(X,Y,'b','EdgeColor','c', 'FaceAlpha', 0.5);

patch

Upvotes: 1

Suever
Suever

Reputation: 65430

If you want to create multiple rectangles, you don't want to put the NaN values to separate them, you instead want to put each rectangle's coordinates in a separate column.

X = [X1; X2; X3; X4];

Y =[zeros(size(X1));        10+zeros(size(X2)); ...
    10+zeros(size(X3));     zeros(size(X4))];  

patch(X, Y, 'c')

Also, the third input to patch specifies the color of the faces (FaceColor) but the default EdgeColor is going to be black.

You can specify the parameter/value pairs as additional inputs to patch to specify the desired value for any other parameters (such as EdgeColor).

patch(X, Y, 'c', 'EdgeColor', 'c', 'FaceAlpha', 0.5)

enter image description here

Upvotes: 2

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