Perhaps there is some sort of formula that could be applied to the 2D
coordinate on the mesh such that similar to "undoing" the terrain
scaling to get the corresponding 2D bitmap coordinate by X and Y by
the terrain scaling factores, you can "undo" the subdivision by some
procedure?
This is ultimately what I need to solve this problem...
Ari
On Sep 2, 8:18 pm, Ari Braginsky <[EMAIL PROTECTED]> wrote:
> Li,
>
> Thank you for your post. I'm not sure if your solution is the same as
> the solution that I need for my problem.
>
> To clarify, I'm moving a point around on a mesh that has a bitmap
> image inside of it. When I move that point, I need to track the
> relative position of that point on the bitmap in normal 2D space in
> order to measure the pixel color value at that point.
>
> Because of the subdivision values, the bitmap image inside of the mesh
> is deformed such that when your point is on top of a feature in the
> bitmap mesh, it doesn't exactly line up with the same converted (by
> way of the mesh X and Y scale division method) point on the 2D
> bitmap. It is somewhat off.
>
> I need to be able to adjust for the subdivision distortion.
>
> Is this similar to your problem that was solved with your solution?
>
> Thanks,
> Ari
>
> On Sep 2, 8:06 pm, Li <[EMAIL PROTECTED]> wrote:
>
> > Hey Ari,
>
> > Ive been working with a similar issue in reflections. The solution I used
> > might be useful to you. The particular problem I had was, once I obtained a
> > 3d point that I knew was on the surface of a plane, what would be the 2d
> > coordinates of that point on the plane? The solution involved determining
> > the top side and left side vectors of the plane, obtaining a vector from the
> > top left corner of the plane to the 3d point, and then using dot products to
> > project that vector onto the side vector. That gives you a scalar value that
> > corresponds to the coordinate system transformation of the point.
>
> > If you think it might help you, here is the code:
>
> > //Three vertices.
> > edgePoint = getVertexGlobalPosition(plane.vertices[0],
> > plane);
> > var p2:Number3D = getVertexGlobalPosition(plane.vertices[1],
> > plane);
> > var p3:Number3D = getVertexGlobalPosition(plane.vertices[4],
> > plane);
>
> > //Side vectors.
> > topVector = new Number3D();
> > topVector.sub(p2, edgePoint);
> > sideVector = new Number3D();
> > sideVector.sub(p3, edgePoint);
>
> > wRatio = MovieMaterial(plane.material).movie.width/plane.width;
> > hRatio =
> > MovieMaterial(plane.material).movie.height/plane.height;
>
> > //TRANSLATE GLOBAL TO PLANE.
> > //Translates a world 3D point to a corresponding 2D point on
> > the plane's material.
> > private function
> > translateGlobalToPlane(point:Number3D):Point
> > {
> > /*
> > Finds a vector from one of the corners of the plane
> > to the point,
> > and projects this vector on its sides, considering
> > scaling.
> > */
> > var v:Number3D = new Number3D();
> > v.sub(point, edgePoint);
> > return new
> > Point(wRatio*v.dot(topVector)/topVector.modulo, hRatio*(this.height -
> > v.dot(sideVector)/sideVector.modulo));
> > }
>
> > //GET VERTEX GLOBAL POSITION.
> > //Translates vertex coordinates to world coordinates.
> > private function getVertexGlobalPosition(vertex:Vertex,
> > vertexContainer:Object3D):Number3D
> > {
> > var m:Matrix3D = new Matrix3D();
> > m.tx = vertex.x;
> > m.ty = vertex.y;
> > m.tz = vertex.z;
> > m.multiply(vertexContainer.transform, m);
> > return new Number3D(m.tx, m.ty, m.tz);
> > }
>
> > On Tue, Sep 2, 2008 at 9:34 PM, Ari Braginsky <[EMAIL PROTECTED]> wrote:
>
> > > I'm having an issue retrieving 2D coordinates off of a mesh based on a
> > > 3D object's position on the mesh.
>
> > > You can normally retrieve the 2D coordinates on the bitmap making up
> > > the mesh by dividing the coordinates of the object by the mesh's X and
> > > Y scale values (see extrusions/CollisionMap.as class).
>
> > > However, if you look at the position on the mesh and compare it to the
> > > raw bitmap, due to some deformations that happen to the mesh with
> > > certain subdivision values, the objects that appear in the bitmap
> > > don't line up with the 2D coordinates on the raw bitmap. If you tweak
> > > the subdivision values, the objects on the bitmap in the mesh move
> > > around/get squashed/etc.
>
> > > Example:
>
> > > Create a bitmap with a circle in the center filled with the color red.
>
> > > Create an elevation using a flat height map and use the bitmap for its
> > > skin.
>
> > > When rendered in 3D, you will see the red circle in the center of the
> > > mesh. If you move your mouse over it, you can translate the 3D
> > > coordinates into 2D space and divide them by the mesh's X and Y scale
> > > values to get the real coordinates on the raw bitmap.
>
> > > What I'm seeing with subdivision values X = 200 and y = 200 is that my
> > > point on the mesh doesn't correlate to the same point on the 2D bitmap
> > > when I convert the 3D coordinates to 2D, taking into account the mesh
> > > scale values.
>
> > > Is there something else I need to do to account for the subdivision
> > > values?
>
> > > If I didn't want any deformation of the mesh, are there subdivision
> > > values I can use such that 3D points on the mesh would exactly match
> > > up with 2D points on the associated bitmap?
>
> > > Thanks,
> > > Ari
