Thinking of writing a perspective tool for krita

[Brendan Scott]

On 25/04/15 19:36, Wolthera wrote:
> Sorry, the ellipse's horizontal component needs to be aligned to the
> horizon of that particular plane.
>
> There's a thread here which goes into the complexer details:
> http://www.conceptart.org/forums/showthread.php/273023-creating-a-perfect-square-in-perspective

Actually, I don't think it's possible for an ellipsoid construction method
relying only (in 1p perspective) on a vanishing point, horizon line and
edge to be replicated to work.

Perspective views represent what a viewer experiences when they stand a
certain distance from the object (call it a cube). As the viewer moves
closer and further away from the object the horizon line (the height of
their eye) and the vanishing point (the point in the middle of their
line of sight) stay the same but the perspective of the object changes.
This means that the vanishing point, horizon line and location of the
near edge of the cube are _not sufficient_ to determine the perspective
depth of the receding edge. There is literally not enough information.

You can draw an ellipse and the tangents to the vanishing points will
make a square in _some_ perspective. But the aim is to draw a square in
a predetermined perspective so that the square shares the same
perspective as the rest of the scene. That's the problem.