## 2011-08-02

### Beer mat logic

Well, the polygon library has been through a lot, and still remains "almost working", which is about as useful as "not working at all". Once again I can see the light at the end of the tunnel and once again it looks quite a long way off.

So, again, rather than plough ahead in to a complicated final solution I am going to try and sort this with a tried and trusted technique, usually involving pens and beer mats.

In practice the plan is to take some paper and pens along rather than actually use beer mats. I may have to find paper with a square grid on it. But the venue should be appropriate as it is the Great British Beer Festival in Earl's Court, tomorrow afternoon.

I suspect I will get lots of helpful advice from my friends on this problem and I am sure a lot of squiggly lines will be drawn...

1. Well, I did tinker more before we go to the beer festival, but to no avail. I now have it deciding two lines cross, so slicing 10^-18mm off the end of a line, and deciding it still crosses, rinse/repeat... Using long long (integer) maths does indeed solve that and is quicker, so that is likely to be the long term solution. But still not quite right in others. Arrrg

Lets hope beer mat logic works. Though my son tells me it is "napkin" logic now as he did not even know what a beer mat was!

2. Are you trying to create horizontal slices through your object, so you know where to put plastic? If so, couldn't you do that just by scripting Blender?

First of all, you put Blender into a top-down orthographic view. You then create a large cuboid and position it so that it overlaps your object. It should completely cover it in the x and y directions, while partially covering it in the z direction. You then use the difference modifier to cut off the part of your original mesh that is overlapped by the cuboid. Finally you select all the coplanar faces which were created by the difference modifier, and set the material to something that will give you a distinctive colour.

This has given you one slice through the object. You now move the cuboid one unit in the z direction and repeat, to get the next slice.

3. On 'beer mat' vs 'napkin' logic, I guess 'back of fag packet' cannot be used in a public place anymore.

4. I predict that towards the end of the day you'll have a breakthrough and come home confident that you're ready to code the ultimate 3D library. I further predict that the following morning your notes won't make any sense whatsoever.

5. Interesting discussions were had, and now it is so 'king hot I am heading home.

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