1 Name 2 3 EXT_blend_minmax 4 5 Name Strings 6 7 GL_EXT_blend_minmax 8 9 Version 10 11 Last Modified Date: September 17, 2009 12 Version: 1.5 13 14 Number 15 16 OpenGL Extension #37 17 OpenGL ES Extension #65 18 19 Dependencies 20 21 There is an interaction with OpenGL ES. 22 23 Overview 24 25 Blending capability is extended by respecifying the entire blend 26 equation. While this document defines only two new equations, the 27 BlendEquationEXT procedure that it defines will be used by subsequent 28 extensions to define additional blending equations. 29 30 The two new equations defined by this extension produce the minimum 31 (or maximum) color components of the source and destination colors. 32 Taking the maximum is useful for applications such as maximum projection 33 in medical imaging. 34 35 Issues 36 37 * I've prefixed the ADD token with FUNC, to indicate that the blend 38 equation includes the parameters specified by BlendFunc. (The min 39 and max equations don't.) Is this necessary? Is it too ugly? 40 Is there a better way to accomplish the same thing? 41 42 New Procedures and Functions 43 44 void BlendEquationEXT(enum mode); 45 46 New Tokens 47 48 Accepted by the <mode> parameter of BlendEquationEXT: 49 50 FUNC_ADD_EXT 0x8006 51 MIN_EXT 0x8007 52 MAX_EXT 0x8008 53 54 Accepted by the <pname> parameter of GetBooleanv, GetIntegerv, 55 GetFloatv, and GetDoublev: 56 57 BLEND_EQUATION_EXT 0x8009 58 59 Additions to Chapter 2 of the GL Specification (OpenGL Operation) 60 61 None 62 63 Additions to Chapter 3 of the GL Specification (Rasterization) 64 65 None 66 67 Additions to Chapter 4 of the GL Specification (Per-Fragment Operations 68 and the Framebuffer) 69 70 The GL Specification defines a single blending equation. This 71 extension introduces a blend equation mode that is specified by calling 72 BlendEquationEXT with one of three enumerated values. The default 73 value FUNC_ADD_EXT specifies that the blending equation defined in 74 the GL Specification be used. This equation is 75 76 C' = (Cs * S) + (Cd * D) 77 78 / 1.0 C' > 1.0 79 C = ( 80 \ C' C' <= 1.0 81 82 where Cs and Cd are the source and destination colors, and S and D are 83 as specified by BlendFunc. 84 85 If BlendEquationEXT is called with <mode> set to MIN_EXT, the 86 blending equation becomes 87 88 C = min (Cs, Cd) 89 90 Finally, if BlendEquationEXT is called with <mode> set to MAX_EXT, the 91 blending equation becomes 92 93 C = max (Cs, Cd) 94 95 In all cases the blending equation is evaluated separately for each 96 color component. 97 98 Additions to Chapter 5 of the GL Specification (Special Functions) 99 100 None 101 102 Additions to Chapter 6 of the GL Specification (State and State Requests) 103 104 None 105 106 Additions to the GLX Specification 107 108 None 109 110 GLX Protocol 111 112 A new GL rendering command is added. The following command is sent to the 113 server as part of a glXRender request: 114 115 BlendEquationEXT 116 2 8 rendering command length 117 2 4097 rendering command opcode 118 4 ENUM mode 119 120 Dependencies on OpenGL ES 121 122 If the GL is OpenGL ES, only the new MIN_EXT and MAX_EXT blend equations 123 are introduced by this extension. BlendEquationOES, FUNC_ADD_OES, and 124 BLEND_EQUATION_OES are introduced by the OES_blend_subtract extension, 125 which is required for this extension to operate. Alternatively, 126 OpenGL ES 2.0 is required, which introduces BlendEquation, FUNC_ADD, and 127 BLEND_EQUATION without the suffixes. 128 129 MIN_EXT and MAX_EXT should be added to Table 4.blendeq described in the 130 OES_blend_subtract extension specification, and Table 4.1 of the OpenGL 131 ES 2.0 specification. 132 133 Mentions of GetDoublev, Begin/End, and GLX in this extension specification 134 can be ignored for OpenGL ES. Also, BlendEquationEXT and FUNC_ADD_EXT 135 instead have the OES suffix courtesy of OES_blend_subtract, or no suffix 136 courtesy of core OpenGL ES 2.0. 137 138 Errors 139 140 INVALID_ENUM is generated by BlendEquationEXT if its single parameter 141 is not FUNC_ADD_EXT, MIN_EXT, or MAX_EXT. 142 143 INVALID_OPERATION is generated if BlendEquationEXT is executed between 144 the execution of Begin and the corresponding execution to End. 145 146 New State 147 148 Get Value Get Command Type Initial Value Attribute 149 --------- ----------- ---- ------------- --------- 150 BLEND_EQUATION_EXT GetIntegerv Z3 FUNC_ADD_EXT color-buffer 151 152 New Implementation Dependent State 153 154 None 155 156 Revision History 157 158 Version 1.5, September 17, 2009 (Jon Leech) - 159 Merge into OpenGL Registry version of the extension and assign 160 OpenGL ES extension number. 161 Version 1.4, May 19, 2009 (Benj Lipchak) - 162 Adapted for OpenGL ES. 163 Version 1.3, May 31, 1995 - 164 Last SGI revision. 165
