Record TTriangle

Geometry of this item. We need two geometry descriptions:

• Local is based on initial Triangle, given when constructing this TTriangle. It's constant for this TTriangle. It's used by octree collision routines, that is things like TBaseTrianglesOctree.SphereCollision, TBaseTrianglesOctree.RayCollision and such expect parameters in the same coord space.

  This may be local coord space of this shape (this is used by TShape.OctreeTriangles) or world coord space (this is used by TCastleSceneCore.OctreeTriangles).

• World is the geometry of Local transformed to be in world coordinates. Initially, World is just a copy of Local.

  If Local already contains world-space geometry, then World can just remain constant, and so is always Local copy.

  If Local contains local shape-space geometry, then World will have to be updated by TTriangle.UpdateWorld whenever some octree item's geometry will be needed in world coords. This will have to be done e.g. by TBaseTrianglesOctree.XxxCollision for each returned item.

Geometry of this item. We need two geometry descriptions:

• Local is based on initial Triangle, given when constructing this TTriangle. It's constant for this TTriangle. It's used by octree collision routines, that is things like TBaseTrianglesOctree.SphereCollision, TBaseTrianglesOctree.RayCollision and such expect parameters in the same coord space.

  This may be local coord space of this shape (this is used by TShape.OctreeTriangles) or world coord space (this is used by TCastleSceneCore.OctreeTriangles).

• World is the geometry of Local transformed to be in world coordinates. Initially, World is just a copy of Local.

  If Local already contains world-space geometry, then World can just remain constant, and so is always Local copy.

  If Local contains local shape-space geometry, then World will have to be updated by TTriangle.UpdateWorld whenever some octree item's geometry will be needed in world coords. This will have to be done e.g. by TBaseTrianglesOctree.XxxCollision for each returned item.

Shape containing this triangle. This is always an instance of TShape class, but due to unit dependencies it cannot be declared as such here. Use CastleShapes unit to have a "record helper" method that returns a Shape as TShape instance.

Tag of an object (like a ray or a line segment) for which we have saved an intersection result. Intersection result is in MailboxIsIntersection, MailboxIntersection, MailboxIntersectionDistance.

To make things correct, we obviously assume that every segment and ray have different tags. Also, tag -1 is reserved. In practice, we simply initialize MailboxSavedTag to -1, and each new segment/ray get consecutive tags starting from 0.

History: a naive implementation at the beginning was not using tags, instead I had MailboxState (empty, ray or segment) and I was storing ray/line vectors (2 TVector3 values). This had much larger size (6 * SizeOf(Single) + SizeOf(enum) = 28 bytes) than tag, which is important (3D models have easily thousands of TTriangle). And it took longer to compare and assign, so it was working much slower.

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Normal vectors, at each triangle vertex.

Texture coordinates, for each triangle point.

Each texture coordinate is a 4D vector, since we may have 3D textures referenced by 4D (homogeneous) coordinates. For normal 2D textures, you can simply take the first 2 components of the vector, and ignore the remaining 2 components. The 3th component is always 0 if was not specified (if model had only 2D texture coords). The 4th component is always 1 if was not specified (if model had only 2D or 3D texture coords).

In case of multi-texturing, this describes coordinates of the first texture unit. In case no texture is defined, this is undefined.

The indexes of this face, for editing / removing it. See TFaceIndex.

Initialize new triangle. Given ATriangle must satisfy ATriangle.IsValid.

Check collisions between TTriangle and ray/segment.

Always use these routines to check for collisions, to use mailboxes if possible. Mailboxes are used only if this was compiled with TRIANGLE_OCTREE_USE_MAILBOX defined.

Increments TriangleCollisionTestsCounter if actual test was done (that is, if we couldn't use mailbox to get the result quickier).

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For a given position (in world coordinates), return the texture coordinate at this point. It is an interpolated texture coordinate from our per-vertex texture coordinates in TexCoord field.

This assumes that Position actually lies within the triangle.

The ITexCoord2D returns the same, but cut to the first 2 texture coordinate components. Usable for normal 2D textures.

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For a given position (in world coordinates), return the smooth normal vector at this point. It is an interpolated normal from our per-vertex normals in the Normal field, thus is supports also the case when you have smooth shading (normals change throughout the triangle).

Like the Normal field, the returned vector is a normal vector in the local coordinates. Use TTriangleHelper.INormalWorldSpace to get a normal vector in scene coordinates.

This assumes that Position actally lies within the triangle.

Like INormal, but not necessarily normalized.