scaling of flat primitives

[Ingolf Weisheit]

Hallo,

in http://www.ldraw.org/library/primref/ the following is mentioned: "To avoid matrix arithmetic problems in some renderers, the third dimension ({y} in the default orientation) must be given a scaling factor of 1."

Is it that strict or is a -1 allowed as well?

The reason for the question is that I'm still working on 11767. If I fix the BFC and I mirror or rotate a primitive I get a -1 as scaling factor for y. Is it legal or is it prefered to have a 0 BFC INVERTNEXT statement for many lines of code?

regards, Ingolf

[Santeri Piippo]

Both 1 and -1 are legal for flat primitives, yes.

[Michael Heidemann]

The current version of DATHeader finds those "scaled flat subfiles" and will correct this.

[Mark Kennedy]

If you use BFC the sign on the flat dimension will effect which face is displayed so if 1 shows the front -1 will show the back.

[Philippe Hurbain]

\"To avoid matrix arithmetic problems in some renderers, the third dimension ({y} in the default orientation) must be given a scaling factor of 1.\"

Actually I don't think that coefficient in flat direction does matter - except that it shouldn't be 0 (a lot of old LDraw part did have this issue), and of course sign impacts BFC as mentionned by Mark. But anyway we now have a tool that does care for us - thanks, Mike!