1 Name 2 3 CHROMIUM_bind_uniform_location 4 5 Name Strings 6 7 GL_CHROMIUM_bind_uniform_location 8 9 Version 10 11 Last Modifed Date: June 20, 2012 12 13 Dependencies 14 15 OpenGL ES 2.0 is required. 16 17 Overview 18 19 This extension is simlar to glBindAttribLocation but instead 20 lets you choose a location for a uniform. This allows you 21 to not have to query the locations of uniforms. 22 23 This allows the client program to know the locations of uniforms 24 without having to wait for shaders to compile or GLSL programs to 25 link to query the locations and therefore have no blocking calls 26 when initializing programs. 27 28 Issues 29 30 If a uniform is an array you can only call glBindUniformLocation 31 for the location of the first element. Other elements' locations 32 must be queried if you need them. Often this is not an issue 33 because you can set all the elements with a single gl call from 34 the first location. 35 36 Good Example: 37 38 --shader-- 39 uniform float u_someArray[4]; 40 41 --C-- 42 GLint location = 123; 43 glBindUniformLocation(program, location, "u_someArray"); 44 glLinkProgram(program); 45 glUseProgram(program); 46 47 // set all 4 floats in u_someArray 48 float values[] = { 0.1f, 0.2f, 0.3f, 0.4f, }; 49 glUniform1fv(location, 4, values); 50 51 Bad example 1: 52 53 GLint location = 123; 54 glBindUniformLocation(program, location, "u_someArray"); 55 glLinkProgram(program); 56 glUseProgram(program); 57 58 // set floats in u_someArray one at a time 59 glUniform1f(location, 0.1f); 60 glUniform1f(location + 1, 0.2f); // ERROR! math not allowed on locations 61 62 Bad example 2: 63 64 GLint location0 = 123; 65 GLint location1 = 124; 66 glBindUniformLocation(program, location0, "u_someArray[0]"); 67 glBindUniformLocation(program, location1, "u_someArray[1]"); // ERROR! 68 // not allowed to assign locations to array elements 69 70 If you need to set individual elements of a uniform array you must query the 71 location of the each element you wish to set. 72 73 New Tokens 74 75 None 76 77 New Procedures and Functions 78 79 void BindUniformLocationCHROMIUM (GLuint program, GLint location, 80 const GLhchar* name); 81 82 specifes that the uniform variable named <name> in program <program> 83 should be bound to uniform location <location> when the program is next 84 linked. If <name> was bound previously, its assigned binding is replaced 85 with <location>. <name> must be a null terminated string. The error 86 INVALID_VALUE is generated if <location> is equal or greater than 87 88 (MAX_VERTEX_UNIFORM_VECTORS + MAX_FRAGMENT_UNIFORM_VECTORS) * 4 89 90 or less than 0. BindUniformLocation has no effect until the program is 91 linked. In particular, it doesn't modify the bindings of active uniforms 92 variables in a program that has already been linked. 93 94 The error INVALID_OPERATION is generated if name starts with the reserved 95 "gl_" prefix. The error INVALID_VALUE is generated if name ends with 96 an array element expression other than "[0]". 97 98 When a program is linked, any active uniforms without a binding specified 99 through BindUniformLocation will be automatically be bound to locations by 100 the GL. Such bindings can be queried using the command 101 GetUniformLocation. 102 103 BindUniformLocation may be issued before any shader objects are attached 104 to a program object. Hence it is allowed to bind any name (except a name 105 starting with "gl_") to an index, including a name that is never used as a 106 uniform in any shader object. Assigned bindings for uniform variables 107 that do not exist or are not active are ignored. 108 109 It is possible for an application to bind more than one uniform name to 110 the same location. This is referred to as aliasing. This will only work 111 if only one of the aliased uniforms is active in the executable program, 112 or if no path through the shader consumes more than one uniform of a set 113 of uniforms aliased to the same location. A link error can occur if the 114 linker determines that every path through the shader consumes multiple 115 aliased uniforms, but implementations are not required to generate an 116 error in this case. The compiler and linker are allowed to assume that no 117 aliasing is done, and may employ optimizations that work only in the 118 absence of aliasing. 119 120 Errors 121 122 None. 123 124 New State 125 126 None. 127 128 Revision History 129 130 7/20/2012 Documented the extension 131 132
