1Name 2 3 EXT_blend_subtract 4 5Name Strings 6 7 GL_EXT_blend_subtract 8 9Version 10 11 $Date: 1995/03/31 04:40:39 $ $Revision: 1.4 $ 12 13Number 14 15 38 16 17Dependencies 18 19 EXT_blend_minmax affects the definition of this extension 20 21Overview 22 23 Two additional blending equations are specified using the interface 24 defined by EXT_blend_minmax. These equations are similar to the 25 default blending equation, but produce the difference of its left 26 and right hand sides, rather than the sum. Image differences are 27 useful in many image processing applications. 28 29New Procedures and Functions 30 31 None 32 33New Tokens 34 35 Accepted by the <mode> parameter of BlendEquationEXT: 36 37 FUNC_SUBTRACT_EXT 0x800A 38 FUNC_REVERSE_SUBTRACT_EXT 0x800B 39 40Additions to Chapter 2 of the GL Specification (OpenGL Operation) 41 42 None 43 44Additions to Chapter 3 of the GL Specification (Rasterization) 45 46 None 47 48Additions to Chapter 4 of the GL Specification (Per-Fragment Operations 49and the Framebuffer) 50 51 Two additional blending equations are defined. If BlendEquationEXT is 52 called with <mode> set to FUNC_SUBTRACT_EXT, the blending equation 53 becomes 54 55 C' = (Cs * S) - (Cd * D) 56 57 / 0.0 C' < 0.0 58 C = ( 59 \ C' C' >= 0.0 60 61 where Cs and Cd are the source and destination colors, and S and D are 62 as specified by BlendFunc. 63 64 If BlendEquationEXT is called with <mode> set to 65 FUNC_REVERSE_SUBTRACT_EXT, the blending equation becomes 66 67 C' = (Cd * D) - (Cs * S) 68 69 / 0.0 C' < 0.0 70 C = ( 71 \ C' C' >= 0.0 72 73 In all cases the blending equation is evaluated separately for each 74 color component. 75 76Additions to Chapter 5 of the GL Specification (Special Functions) 77 78 None 79 80Additions to Chapter 6 of the GL Specification (State and State Requests) 81 82 None 83 84Additions to the GLX Specification 85 86 None 87 88GLX Protocol 89 90 None 91 92Dependencies on EXT_blend_minmax 93 94 If this extension is supported, but EXT_blend_minmax is not, then 95 this extension effectively defines the procedure BlendEquationEXT, its 96 parameter FUNC_ADD_EXT, and the query target BLEND_EQUATION_EXT, as 97 described in EXT_blend_minmax. It is therefore as though 98 EXT_blend_minmax were also supported, except that equations MIN_EXT 99 and MAX_EXT are not supported. 100 101Errors 102 103 INVALID_ENUM is generated by BlendEquationEXT if its single parameter 104 is not FUNC_ADD_EXT, MIN_EXT, MAX_EXT, FUNC_SUBTRACT_EXT, or 105 FUNC_REVERSE_SUBTRACT_EXT. 106 107 INVALID_OPERATION is generated if BlendEquationEXT is executed between 108 the execution of Begin and the corresponding execution to End. 109 110New State 111 112 Get Value Get Command Type Initial Value Attribute 113 --------- ----------- ---- ------------- --------- 114 BLEND_EQUATION_EXT GetIntegerv Z5 FUNC_ADD_EXT color-buffer 115 116New Implementation Dependent State 117 118 None 119