Class OESGeometryShader

  • public class OESGeometryShader
    extends java.lang.Object
    Native bindings to the OES_geometry_shader extension.

    OES_geometry_shader defines a new shader type available to be run on the GPU, called a geometry shader. Geometry shaders are run after vertices are transformed, but prior to color clamping, flatshading and clipping.

    A geometry shader begins with a single primitive (point, line, triangle). It can read the attributes of any of the vertices in the primitive and use them to generate new primitives. A geometry shader has a fixed output primitive type (point, line strip, or triangle strip) and emits vertices to define a new primitive. A geometry shader can emit multiple disconnected primitives. The primitives emitted by the geometry shader are clipped and then processed like an equivalent primitive specified by the application.

    Furthermore, OES_geometry_shader provides four additional primitive types: lines with adjacency, line strips with adjacency, separate triangles with adjacency, and triangle strips with adjacency. Some of the vertices specified in these new primitive types are not part of the ordinary primitives, instead they represent neighboring vertices that are adjacent to the two line segment end points (lines/strips) or the three triangle edges (triangles/tstrips). These vertices can be accessed by geometry shaders and used to match up the vertices emitted by the geometry shader with those of neighboring primitives.

    Since geometry shaders expect a specific input primitive type, an error will occur if the application presents primitives of a different type. For example, if a geometry shader expects points, an error will occur at drawing time if a primitive mode of TRIANGLES is specified.

    This extension also adds the notion of layered framebuffer attachments and framebuffers that can be used in conjunction with geometry shaders to allow programs to direct primitives to a face of a cube map or layer of a three-dimensional texture or two-dimensional array texture. The layer used for rendering can be selected by the geometry shader at run time. The framebuffer layer count present in GL 4.x and removed from ES 3.1 is restored.

    Not all geometry shader implementations have the ability to write the point size from a geometry shader. Thus a second extension string and shading language enable are provided for implementations which do support geometry shader point size.

    This extension relies on the OES_shader_io_blocks extension to provide the required functionality for declaring input and output blocks and interfacing between shaders.

    Requires GLES 3.1 and OES_shader_io_blocks or EXT_shader_io_blocks.