Using the patch command u can plot as many triangular or rectangular shapes at the same time.
Just build the grid (i.e. the 'vertices') and the a conectivity matrix (i.e. 'faces') to connect selected points from the grid.
% create a random grid
MyGrid = [-3.01 -2.82; % node 1
1.33 -1.31; % node 2
0.70 1.79; % node 3
-2.46 2.46]; % node4
figure
subplot(1,2,1)
patch('Faces', [1 2 3 4], 'Vertices', MyGrid,'FaceColor','none')
grid on
subplot(1,2,2)
patch('Faces', [1 2 4], 'Vertices', MyGrid,'FaceColor','none')
grid on
