Why did this subtract problem happen?

Well, I bet both you and me are getting bored with me posting "Xara is inaccurate" topics every now and then, so I'll prompt you with a question instead, so perhaps I can get a nice solution to avoid this in the future!

I was recommended by another thread here to achieve a 3D effect by cloning, moving and then adding the clones together and trim a few vertices.

This worked, but now I wanted to subtract/slice the original shape from my newly created "3D volume" so I could shade the parts independently.

If you open the attached file, and then subtract the green object from the red (or slice, but subtracting is easier to see), notice the "garbage" objects produced. (For extra credit, hehe, also notice how the previously cloned and added object produced a little overlap in the corners.)

So, why did this subtract problem happen?

Well, I bet both you and me are getting bored with me posting "Xara is inaccurate" topics every now and then, so I'll prompt you with a question instead, so perhaps I can get a nice solution to avoid this in the future!

I was recommended by another thread here to achieve a 3D effect by cloning, moving and then adding the clones together and trim a few vertices.

This worked, but now I wanted to subtract/slice the original shape from my newly created "3D volume" so I could shade the parts independently.

If you open the attached file, and then subtract the green object from the red (or slice, but subtracting is easier to see), notice the "garbage" objects produced. (For extra credit, hehe, also notice how the previously cloned and added object produced a little overlap in the corners.)

So, why did this subtract problem happen?

One is always getting innacuracies when trying to display, remove, substracting and defining "analog" objects by digital means. MAth in computer is only "this" exact. It can never be so accurate as real world (unles someone produdec some bio or analog computers maybe?). Circle is mathematically defined by flotating point math and what you see on screen is as close as possible definition of the circle in a pixel grid which is on the contrary strongly digital... ;-)

But seriously, I've tried to substract cloned circle from the original circle.. both should be exactly the same, so there should be zero result after substraction, but "garbage" was also there... so if I were you, I would reconcile with this feature and learned to use shape tool to be able to select and delete the garbage nodes whenever it is necessary http://www.talkgraphics.com/images/smilies/biggrin.gif http://www.talkgraphics.com/images/smilies/biggrin.gif

I just subtracted the top shape from the shadow without a problem. I did both Combine Shapes... Subtract Shapes and Combine Shapes... Slice Shapes.

I did notice some fringe residue on the red portion however, but you can delete this by selecting the unnecessary control points with the Shape Editor Tool (the shape needs to be selected with the Selector Tool first).

Gary

Aha! "Fringe residue..."