You could have tried kluid (http://www.kluid.com) for this. Well the 2D slice will be either a square with a circle or a rectangle in it depending from which side you cut the volume. But in case you still want to draw the 3d volume here are the codes for cube (you can easily modify it for cylinder also):

function cube(i,d,c,alpha);
% function to draw a 3-D cube in a 3-D plot
%
%
% cube(start,size,color,alpha);
%
% will draw a cube at 'start' of size 'size' of color 'color' and
% transparency alpha (1 for opaque, 0 for transparent)
% Default size is 1
% Default color is blue
% Default alpha value is 1
%
% start is a three element vector [x,y,z]
% size the a three element vector [dx,dy,dz]
% color is a character string to specify color
% (type 'help plot' to see list of valid colors)
%
%
% cube([2 3 4],[1 2 3],'r',0.7);
% axis([0 10 0 10 0 10]);
%

switch(nargin),
case 0
disp('Too few arguements for cube');
return;
case 1
l=1; %default length of side of cube is 1
c='b'; %default color of cube is blue
case 2,
c='b';
case 3,
alpha=1;
case 4,
%do nothing
otherwise
disp('Too many arguements for cube');
end;
x=[i(1)+[0 0 0 0 d(1) d(1) d(1) d(1)]; ...
i(2)+[0 0 d(2) d(2) 0 0 d(2) d(2)]; ...
i(3)+[0 d(3) 0 d(3) 0 d(3) 0 d(3)]]';
for n=1:3,
if n==3,
x=sortrows(x,[n,1]);
else
x=sortrows(x,[n n+1]);
end;
temp=x(3,: );
x(3,: )=x(4,: );
x(4,: )=temp;
h=patch(x(1:4,1),x(1:4,2),x(1:4,3),c);
set(h,'FaceAlpha',alpha);
temp=x(7,: );
x(7,: )=x(8,: );
x(8,: )=temp;
h=patch(x(5:8,1),x(5:8,2),x(5:8,3),c);
set(h,'FaceAlpha',alpha);
end;


: ]

b4codes

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