drawIndexed

drawIndexed is a fundamental rendering command used in computer graphics, particularly within graphics APIs like DirectX and OpenGL. Its primary purpose is to render a set of triangles by referencing vertices from a vertex buffer using an index buffer. Instead of specifying each vertex's position and attributes directly for every triangle, drawIndexed allows for efficient reuse of vertex data.

The process begins with a vertex buffer, which holds geometric information such as vertex positions, normals, texture coordinates, and colors. Separately, an index buffer stores a sequence of integers. Each integer in the index buffer represents the index of a vertex within the vertex buffer. When drawIndexed is called, the graphics hardware reads the indices from the index buffer. For each index, it retrieves the corresponding vertex data from the vertex buffer. These retrieved vertices are then used to form primitives, typically triangles, which are then rendered to the screen.

The main advantage of drawIndexed is its efficiency in handling geometry with shared vertices. For example, in a complex mesh, many vertices might be shared by multiple triangles. Without indexed drawing, the data for these shared vertices would have to be duplicated for each triangle, leading to larger data sets and increased memory usage. By using an index buffer, each unique vertex is stored only once, and multiple triangles can reference it as needed. This significantly reduces memory bandwidth and the amount of data that needs to be transferred to the graphics processing unit (GPU), resulting in faster rendering performance, especially for detailed models.