glGetActiveUniform

glGetActiveUniform: man3/glGetActiveUniform.xml

glGetActiveUniform returns information about an active uniform variable in the program object specified by program. The number of active uniform variables can be obtained by calling glGetProgram with the value GL_ACTIVE_UNIFORMS. A value of 0 for index selects the first active uniform variable. Permissible values for index range from 0 to the number of active uniform variables minus 1. Shaders may use either built-in uniform variables, user-defined uniform variables, or both. Built-in uniform variables have a prefix of "gl_" and reference existing OpenGL state or values derived from such state (e.g., gl_DepthRangeParameters, see the OpenGL Shading Language specification for a complete list.) User-defined uniform variables have arbitrary names and obtain their values from the application through calls to glUniform. A uniform variable (either built-in or user-defined) is considered active if it is determined during the link operation that it may be accessed during program execution. Therefore, program should have previously been the target of a call to glLinkProgram, but it is not necessary for it to have been linked successfully. The size of the character buffer required to store the longest uniform variable name in program can be obtained by calling glGetProgram with the value GL_ACTIVE_UNIFORM_MAX_LENGTH. This value should be used to allocate a buffer of sufficient size to store the returned uniform variable name. The size of this character buffer is passed in bufSize, and a pointer to this character buffer is passed in name. glGetActiveUniform returns the name of the uniform variable indicated by index, storing it in the character buffer specified by name. The string returned will be null terminated. The actual number of characters written into this buffer is returned in length, and this count does not include the null termination character. If the length of the returned string is not required, a value of null can be passed in the length argument. The type argument will return a pointer to the uniform variable's data type. The symbolic constants returned for uniform types are shown in the table below. Returned Symbolic Contant Shader Uniform Type GL_FLOAT float GL_FLOAT_VEC2 vec2 GL_FLOAT_VEC3 vec3 GL_FLOAT_VEC4 vec4 GL_INT int GL_INT_VEC2 ivec2 GL_INT_VEC3 ivec3 GL_INT_VEC4 ivec4 GL_UNSIGNED_INT unsigned int GL_UNSIGNED_INT_VEC2 uvec2 GL_UNSIGNED_INT_VEC3 uvec3 GL_UNSIGNED_INT_VEC4 uvec4 GL_BOOL bool GL_BOOL_VEC2 bvec2 GL_BOOL_VEC3 bvec3 GL_BOOL_VEC4 bvec4 GL_FLOAT_MAT2 mat2 GL_FLOAT_MAT3 mat3 GL_FLOAT_MAT4 mat4 GL_FLOAT_MAT2x3 mat2x3 GL_FLOAT_MAT2x4 mat2x4 GL_FLOAT_MAT3x2 mat3x2 GL_FLOAT_MAT3x4 mat3x4 GL_FLOAT_MAT4x2 mat4x2 GL_FLOAT_MAT4x3 mat4x3 GL_SAMPLER_1D sampler1D GL_SAMPLER_2D sampler2D GL_SAMPLER_3D sampler3D GL_SAMPLER_CUBE samplerCube GL_SAMPLER_1D_SHADOW sampler1DShadow GL_SAMPLER_2D_SHADOW sampler2DShadow GL_SAMPLER_1D_ARRAY sampler1DArray GL_SAMPLER_2D_ARRAY sampler2DArray GL_SAMPLER_1D_ARRAY_SHADOW sampler1DArrayShadow GL_SAMPLER_2D_ARRAY_SHADOW sampler2DArrayShadow GL_SAMPLER_2D_MULTISAMPLE sampler2DMS GL_SAMPLER_2D_MULTISAMPLE_ARRAY sampler2DMSArray GL_SAMPLER_CUBE_SHADOW samplerCubeShadow GL_SAMPLER_BUFFER samplerBuffer GL_SAMPLER_2D_RECT sampler2DRect GL_SAMPLER_2D_RECT_SHADOW sampler2DRectShadow GL_INT_SAMPLER_1D isampler1D GL_INT_SAMPLER_2D isampler2D GL_INT_SAMPLER_3D isampler3D GL_INT_SAMPLER_CUBE isamplerCube GL_INT_SAMPLER_1D_ARRAY isampler1DArray GL_INT_SAMPLER_2D_ARRAY isampler2DArray GL_INT_SAMPLER_2D_MULTISAMPLE isampler2DMS GL_INT_SAMPLER_2D_MULTISAMPLE_ARRAY isampler2DMSArray GL_INT_SAMPLER_BUFFER isamplerBuffer GL_INT_SAMPLER_2D_RECT isampler2DRect GL_UNSIGNED_INT_SAMPLER_1D usampler1D GL_UNSIGNED_INT_SAMPLER_2D usampler2D GL_UNSIGNED_INT_SAMPLER_3D usampler3D GL_UNSIGNED_INT_SAMPLER_CUBE usamplerCube GL_UNSIGNED_INT_SAMPLER_1D_ARRAY usampler2DArray GL_UNSIGNED_INT_SAMPLER_2D_ARRAY usampler2DArray GL_UNSIGNED_INT_SAMPLER_2D_MULTISAMPLE usampler2DMS GL_UNSIGNED_INT_SAMPLER_2D_MULTISAMPLE_ARRAY usampler2DMSArray GL_UNSIGNED_INT_SAMPLER_BUFFER usamplerBuffer GL_UNSIGNED_INT_SAMPLER_2D_RECT usampler2DRect If one or more elements of an array are active, the name of the array is returned in name, the type is returned in type, and the size parameter returns the highest array element index used, plus one, as determined by the compiler and/or linker. Only one active uniform variable will be reported for a uniform array. Uniform variables that are declared as structures or arrays of structures will not be returned directly by this function. Instead, each of these uniform variables will be reduced to its fundamental components containing the "." and "[]" operators such that each of the names is valid as an argument to glGetUniformLocation. Each of these reduced uniform variables is counted as one active uniform variable and is assigned an index. A valid name cannot be a structure, an array of structures, or a subcomponent of a vector or matrix. The size of the uniform variable will be returned in size. Uniform variables other than arrays will have a size of 1. Structures and arrays of structures will be reduced as described earlier, such that each of the names returned will be a data type in the earlier list. If this reduction results in an array, the size returned will be as described for uniform arrays; otherwise, the size returned will be 1. The list of active uniform variables may include both built-in uniform variables (which begin with the prefix "gl_") as well as user-defined uniform variable names. This function will return as much information as it can about the specified active uniform variable. If no information is available, length will be 0, and name will be an empty string. This situation could occur if this function is called after a link operation that failed. If an error occurs, the return values length, size, type, and name will be unmodified.