After you call the Close method, the sink can be discarded and you’re left with an ID2D1Mesh object. The Tessellate method generates triangles that cover the areas enclosed by the geometry. The ID2D1TessellationSink interface has just two methods: AddTriangles (which adds a collection of D2D1_TRIANGLE objects to the collection) and Close, which makes the mesh object immutable.Īlthough your program can call AddTriangles itself, often it will pass the ID2D1TessellationSink object to the Tessellate method defined by the ID2D1Geometry interface: geometry->Tessellate(IdentityMatrix(), tessellationSink) In Direct2D, tessellation is the process of decomposing a two-dimensional area into triangles. In general, “tessellation” refers to the process of covering a surface with a mosaic pattern, but the term is used somewhat differently in Direct2D and Direct3D programming. This method returns an object of type ID2D1TessellationSink: ID2D1TessellationSink * tessellationSink
Tessellation triangle definition code#
(To keep things simple, I’m not showing the use of ComPtr or checking HRESULT values in these brief code examples.) The ID2D1Mesh interface defines a single method named Open. The ID2D1RenderTarget (from which ID2D1DeviceContext derives) supports a method named CreateMesh that creates such an object: ID2D1Mesh * mesh The triangle structure defined in Direct2D is simple: struct D2D1_TRIANGLEĪs far as I can determine, this structure is used in Direct2D only in connection with a “mesh,” which is a collection of triangles stored in an object of type ID2D1Mesh. Or maybe it’s really not that surprising: Because Direct2D is built on top of Direct3D, it seems reasonable for Direct2D to take advantage of the triangle support in Direct3D and the GPU. So it’s somewhat surprising to find triangles pop up in a rather obscure corner of Direct2D. In contrast, triangles aren’t found at all in most 2D graphics programming interfaces, where the most common two-dimensional primitives are lines, curves, rectangles and ellipses. Much of the work performed by a modern graphics processing unit (GPU) involves rendering triangles, so of course Direct3D programming involves working with triangles to define solid figures. Triangles are ubiquitous in 3D computer graphics. This is how triangles are shaded to mimic the reflection of light seen in real-world objects. The illusion of curvature is enhanced by exploiting another characteristic of triangles: If the three vertices of a triangle are associated with three different values-for example, three different colors or three different geometric vectors-these values can be interpolated over the surface of the triangle and used to color that surface. Of course, the surfaces of real-world objects are often curved, but if you make the triangles small enough, they can approximate curved surfaces to a degree sufficient to fool the human eye. Assembling a seemingly solid figure from triangle “building blocks” is the most fundamental process in 3D computer graphics. In 3D graphics programming, triangles form the surfaces of solid figures, starting with the simplest of all three-dimensional figures, the triangular pyramid, or tetrahedron. But that square can be divided into two triangles, each of which is flat, although not necessarily on the same plane. A square in 3D space isn’t guaranteed to be flat because the fourth point might not be in the same plane as the other three. Indeed, one way to define a plane in 3D space is with three non-collinear points, and that’s a triangle. On the other hand, any other type of polygon can be decomposed into a collection of triangles.Įven in three dimensions, a triangle is always flat.
It’s nothing more than three points connected by three lines, and if you try to make it any simpler, it collapses into a single dimension.
The triangle is the most basic two-dimensional figure. Volume 29 Number 3 DirectX Factor : Triangles and Tessellation
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