Shear by angle

%adapted from https://octave.sourceforge.io/image/function/imtransform.html
im = [checkerboard(20, 2, 4); checkerboard(40, 1, 2)];

rho = pi/4 % 45°, can't be zero

newpoint = 1 + 1/tan(rho);
p1 = [0 0; 1 0; 1 1];
p2 = [0 0; 1 0; newpoint 1];
T = maketform ('affine', p1, p2);

[im2 xdata ydata] = imtransform (im, T);
imh = imshow (im2); set (imh, 'xdata', xdata, 'ydata', ydata)
set (gca, 'xlim', xdata, 'ylim', ydata)
axis on, hold on, xlabel ('Shear');