Triangle Strips (IFMETriangleStrip)

A triangle strip is a series of connected triangular faces. These faces are defined by three consecutive points in a point list. The first triangular face contains the first three vertices, denoted below by v₁, v₂, and v₃. A new triangle is formed by connecting the next point with its two immediate predecessors. That is, every additional point v_i defines a new triangular face containing vertices v_i-2, v_i–1, and v_i.

For example, the second triangle contains v₂, v₃, and v₄, the third contains v₃, v₄, and v₅, and so on. The following diagram illustrates a typical triangle strip:

In order to maintain a consistent orientation, each successive triangle is defined with opposite orientation. In the diagram above, the vertex order would be (v₁, v₂, v₃) for the first triangle, (v₄, v₃, v₂) for the second, (v₃, v₄, v₅) for the third, and so on. Due to this propagation, the overall orientation of a triangle strip can be determined by the orientation of the first triangle.

For information on how vertex order affects surface normal and front/back surface determination, see Faces. As a consequence of this, some triangle strips can only be directly defined in one direction and cannot be reversed without adding additional geometry under the default right-handed coordinate system (counter-clockwise winding order). In particular, triangle strips with an even length cannot be directly reversed. To mitigate this, triangle strips also store a flipped flag which defines whether the strip should use a left-handed coordinate system (clockwise winding) instead of right-handed.

Triangle strips may store measures on their nodes.

Triangle strips may possess optional front or back appearances, and may be single or double sided.