Solid constraints only work for positive functions

[winstliu]

On line 320 there's this if statement: if(this.equation1.getCoord(i) <= size). It's meant to stop rendering the solid if it goes outside the 28x28 graph size. However this obviously doesn't work for negative functions. A simple fix (such as the one I committed yesterday for a similar bug) would be if(math.abs(this.equation1.getCoord(i)) <= size), though after testing that out I realized that this method provides slight inconsistencies. The correct way would be to do something like the bounds over-extending where the size is modified.

Negative (without "fix"):

Negative (with "fix"):

Positive: