                            2  4   	  f    Name

    blend_subtract

Name Strings

    ARB_imaging

Version

    $Date: 1997/09/22 23:03:27 $ $Revision: 1.1 $

Dependencies

    OpenGL 1.2 is required

Overview

    Two additional blending equations are specified using the BlendEquation
    interface. These equations are similar to the default blending equation,
    but produce the difference of its left and right hand sides, rather than
    the sum. Image differences are useful in many image processing
    applications.

New Procedures and Functions

    None

New Tokens

    Accepted by the <mode> parameter of BlendEquation:

	FUNC_SUBTRACT			 0x800A
	FUNC_REVERSE_SUBTRACT		 0x800B

Additions to Chapter 2 of the GL Specification (OpenGL Operation)

    None

Additions to Chapter 3 of the GL Specification (Rasterization)

    None

Additions to Chapter 4 of the GL Specification (Per-Fragment Operations
and the Framebuffer)

    Two additional blending equations are defined.  If BlendEquation is
    called with <mode> set to FUNC_SUBTRACT, the blending equation becomes

	C' = (Cs * S) - (Cd * D)

	     /	0.0	C' < 0.0
	C = (
	     \	 C'	C' >= 0.0

    where Cs and Cd are the source and destination colors, and S and D are
    as specified by BlendFunc.

    If BlendEquation is called with <mode> set to FUNC_REVERSE_SUBTRACT, the
    blending equation becomes

	C' = (Cd * D) - (Cs * S)

	     /	0.0	C' < 0.0
	C = (
	     \	 C'	C' >= 0.0

    In all cases the blending equation is evaluated separately for each
    color component.

Additions to Chapter 5 of the GL Specification (Special Functions)

    None

Additions to Chapter 6 of the GL Specification (State and State Requests)

    None

Additions to the GLX Specification

    None

GLX Protocol

    None

Errors

    INVALID_ENUM is generated by BlendEquation if its single parameter is
    not FUNC_ADD, MIN, MAX, FUNC_SUBTRACT, or FUNC_REVERSE_SUBTRACT.

    INVALID_OPERATION is generated if BlendEquation is executed between
    the execution of Begin and the corresponding execution to End.

New State

    None

New Implementation Dependent State

    None
TEXTMOSS  ? {                 