On 3/24/07, Thorsten Wilms <t_w_@...123...> wrote:

The perspective is either impossible or it's not a box, so much is obvious for me.

Ah, perhaps you mean that the green VP must be on the other side. But, Inkscape is under no obligation to represent only "possible" perspectives :) Just drag the VP down where _you_ want it to be according to your rules :) Others will probably find uses for such "impossible" perspectives.

But perhaps allowing such weird stuff makes things easier in the end.

Yes, let's not introduce any limitations unless absolutely necessary.

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We don't yet have the notion of horizon at all, at least at this basic stage. Any pair of VPs can be taken to represent a horizon.

The horizon is important. Take several boxes with non-parallel side walls as example: their VPs have to be on the same horizon.

Yes, and it's easy to make a regular guideline and to snap all VPs to it. No need to add anything special to the 3D tool for that.

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as the user will likely care more about the box. Because if you draw on paper, using construction boxes/lines, at least one VP would be far away from the paper in most cases.

So what? In Inkscape you can always zoom out as far as you need and still drag it freely.

My point was not about a technical limitation, but the common practical approach to drawing in perspective: you draw a box and the VPs remain in your imagination only. The angles of the edges step into the fore- ground.

That's because on paper, you can't just grab the VP and drag it. So you think in terms of angles. But when you can drag it, it's much easier IMHO :)

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When you drag a corner, you change the size/proportion of the box but its perspective (i.e. VPs) remains the same. When you drag the VPs, you change perspective but the box size/proportions remain the same.

Hmm. I wonder if you can keep proportions and perspective apart at all, if you have no movable camera and no projection from a reference.

That's the whole point of this tool. Our proposal is that yes, it's possible. We will try to prove it by coding :)

First image, if I drag the lower front corner, do I change perspective or proportions?

You make the box taller, but all VPs stay unomved.