OpenGL.GL.NV.vertex_program2
OpenGL extension NV.vertex_program2
This module customises the behaviour of the
OpenGL.raw.GL.NV.vertex_program2 to provide a more
Python-friendly API
Overview (from the spec)
This extension further enhances the concept of vertex programmability
introduced by the NV_vertex_program extension, and extended by
NV_vertex_program1_1. These extensions create a separate vertex program
mode where the configurable vertex transformation operations in unextended
OpenGL are replaced by a user-defined program.
This extension introduces the VP2 execution environment, which extends the
VP1 execution environment introduced in NV_vertex_program. The VP2
environment provides several language features not present in previous
vertex programming execution environments:
- Branch instructions allow a program to jump to another instruction specified in the program.
- Branching support allows for up to four levels of subroutine calls/returns.
- A four-component condition code register allows an application to compute a component-wise write mask at run time and apply that mask to register writes.
- Conditional branches are supported, where the condition code register is used to determine if a branch should be taken.
- Programmable user clipping is supported support (via the CLP0-CLP5 clip distance registers). Primitives are clipped to the area where the interpolated clip distances are greater than or equal to zero.
- Instructions can perform a component-wise absolute value operation on any operand load.
The VP2 execution environment provides a number of new instructions, and
extends the semantics of several instructions already defined in
NV_vertex_program.
- ARR: Operates like ARL, except that float-to-int conversion is done by rounding. Equivalent results could be achieved (less efficiently) in NV_vertex program using an ADD/ARL sequence and a program parameter holding the value 0.5.
- BRA, CAL, RET: Branch, subroutine call, and subroutine return instructions.
- COS, SIN: Adds support for high-precision sine and cosine computations.
- FLR, FRC: Adds support for computing the floor and fractional portion of floating-point vector components. Equivalent results could be achieved (less efficiently) in NV_vertex_program using the EXP instruction to compute the fractional portion of one component at a time.
- EX2, LG2: Adds support for high-precision exponentiation and logarithm computations.
- ARA: Adds pairs of components of an address register; useful for looping and other operations.
- SEQ, SFL, SGT, SLE, SNE, STR: Add six new "set on" instructions, similar to the SLT and SGE instructions defined in NV_vertex_program. Equivalent results could be achieved (less efficiently) in NV_vertex_program with multiple SLT, SGE, and arithmetic instructions.
- SSG: Adds a new "set sign" operation, which produces a vector holding negative one for negative components, zero for components with a value of zero, and positive one for positive components. Equivalent results could be achieved (less efficiently) in NV_vertex_program with multiple SLT, SGE, and arithmetic instructions.
- The ARL instruction is extended to operate on four components instead of a single component.
- All instructions that produce integer or floating-point result vectors have variants that update the condition code register based on the result vector.
This extension also raises some of the resource limitations in the
NV_vertex_program extension.
- 256 program parameter registers (versus 96 in NV_vertex_program).
- 16 temporary registers (versus 12 in NV_vertex_program).
- Two four-component integer address registers (versus one single-component register in NV_vertex_program).
- 256 total vertex program instructions (versus 128 in NV_vertex_program).
- Including loops, programs can execute up to 64K instructions.
The official definition of this extension is available here:
http://www.opengl.org/registry/specs/NV/vertex_program2.txt