GLGETACTIVEUNIFORM(3G)

    .SH "NAME" glGetActiveUniform - Returns information about an active uniform variable for the specified program object
    .SH "C SPECIFICATION"

        .HP u void glGetActiveUniform(GLuint program, GLuint index, GLsizei bufSize, GLsizei *length, GLint *size, GLenum *type, GLchar *name);

    .SH "PARAMETERS"

        .PP program

                Specifies the program object to be queried.

            .RE
            .PP index

                    Specifies the index of the uniform variable to be queried.

                .RE
                .PP bufSize

                        Specifies the maximum number of characters OpenGL is allowed to write in the character buffer indicated by name.

                    .RE
                    .PP length

                            Returns the number of characters actually written by OpenGL in the string indicated by name (excluding the null terminator) if a value other than NULL is passed.

                        .RE
                        .PP size

                                Returns the size of the uniform variable.

                            .RE
                            .PP type

                                    Returns the data type of the uniform variable.

                                .RE
                                .PP name

                                        Returns a null terminated string containing the name of the uniform variable.

                                    .RE

                                .SH "DESCRIPTION"
                                .PP 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 zero to the number of active uniform variables minus one.
                                .PP 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.
                                .PP 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.
                                .PP 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.
                                .PP 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_DOUBLE | double
                            GL_DOUBLE_VEC2 | dvec2
                            GL_DOUBLE_VEC3 | dvec3
                            GL_DOUBLE_VEC4 | dvec4
                            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_DOUBLE_MAT2 | dmat2
                            GL_DOUBLE_MAT3 | dmat3
                            GL_DOUBLE_MAT4 | dmat4
                            GL_DOUBLE_MAT2x3 | dmat2x3
                            GL_DOUBLE_MAT2x4 | dmat2x4
                            GL_DOUBLE_MAT3x2 | dmat3x2
                            GL_DOUBLE_MAT3x4 | dmat3x4
                            GL_DOUBLE_MAT4x2 | dmat4x2
                            GL_DOUBLE_MAT4x3 | dmat4x3
                            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
                            GL_IMAGE_1D | image1D
                            GL_IMAGE_2D | image2D
                            GL_IMAGE_3D | image3D
                            GL_IMAGE_2D_RECT | image2DRect
                            GL_IMAGE_CUBE | imageCube
                            GL_IMAGE_BUFFER | imageBuffer
                            GL_IMAGE_1D_ARRAY | image1DArray
                            GL_IMAGE_2D_ARRAY | image2DArray
                            GL_IMAGE_2D_MULTISAMPLE | image2DMS
                            GL_IMAGE_2D_MULTISAMPLE_ARRAY | image2DMSArray
                            GL_INT_IMAGE_1D | iimage1D
                            GL_INT_IMAGE_2D | iimage2D
                            GL_INT_IMAGE_3D | iimage3D
                            GL_INT_IMAGE_2D_RECT | iimage2DRect
                            GL_INT_IMAGE_CUBE | iimageCube
                            GL_INT_IMAGE_BUFFER | iimageBuffer
                            GL_INT_IMAGE_1D_ARRAY | iimage1DArray
                            GL_INT_IMAGE_2D_ARRAY | iimage2DArray
                            GL_INT_IMAGE_2D_MULTISAMPLE | iimage2DMS
                            GL_INT_IMAGE_2D_MULTISAMPLE_ARRAY | iimage2DMSArray
                            GL_UNSIGNED_INT_IMAGE_1D | uimage1D
                            GL_UNSIGNED_INT_IMAGE_2D | uimage2D
                            GL_UNSIGNED_INT_IMAGE_3D | uimage3D
                            GL_UNSIGNED_INT_IMAGE_2D_RECT | uimage2DRect
                            GL_UNSIGNED_INT_IMAGE_CUBE | uimageCube
                            GL_UNSIGNED_INT_IMAGE_BUFFER | uimageBuffer
                            GL_UNSIGNED_INT_IMAGE_1D_ARRAY | uimage1DArray
                            GL_UNSIGNED_INT_IMAGE_2D_ARRAY | uimage2DArray
                            GL_UNSIGNED_INT_IMAGE_2D_MULTISAMPLE | uimage2DMS
                            GL_UNSIGNED_INT_IMAGE_2D_MULTISAMPLE_ARRAY | uimage2DMSArray
                            GL_UNSIGNED_INT_ATOMIC_COUNTER | atomic_uint

                                .PP 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.
                                .PP 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.
                                .PP 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.
                                .PP 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.
                                .PP 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.

                                .SH "NOTES"
                                    .PP The double types, GL_DOUBLE, GL_DOUBLE_VEC2, GL_DOUBLE_VEC3, GL_DOUBLE_VEC4, GL_DOUBLE_MAT2, GL_DOUBLE_MAT3, GL_DOUBLE_MAT4, GL_DOUBLE_MAT2x3, GL_DOUBLE_MAT2x4, GL_DOUBLE_MAT3x2, GL_DOUBLE_MAT3x4, GL_DOUBLE_MAT4x2, and GL_DOUBLE_MAT4x3 are only available if the GL version is 4.1 or higher.
                                    .PP The image types, GL_IMAGE_1D, GL_IMAGE_2D, GL_IMAGE_3D, GL_IMAGE_2D_RECT, GL_IMAGE_CUBE, GL_IMAGE_BUFFER, GL_IMAGE_1D_ARRAY, GL_IMAGE_2D_ARRAY, GL_IMAGE_2D_MULTISAMPLE, GL_IMAGE_2D_MULTISAMPLE_ARRAY, GL_INT_IMAGE_1D, GL_INT_IMAGE_2D, GL_INT_IMAGE_3D, GL_INT_IMAGE_2D_RECT, GL_INT_IMAGE_CUBE, GL_INT_IMAGE_BUFFER, GL_INT_IMAGE_1D_ARRAY, GL_INT_IMAGE_2D_ARRAY, GL_INT_IMAGE_2D_MULTISAMPLE, GL_INT_IMAGE_2D_MULTISAMPLE_ARRAY, GL_UNSIGNED_INT_IMAGE_1D, GL_UNSIGNED_INT_IMAGE_2D, GL_UNSIGNED_INT_IMAGE_3D, GL_UNSIGNED_INT_IMAGE_2D_RECT, GL_UNSIGNED_INT_IMAGE_CUBE, GL_UNSIGNED_INT_IMAGE_BUFFER, GL_UNSIGNED_INT_IMAGE_1D_ARRAY, GL_UNSIGNED_INT_IMAGE_2D_ARRAY, GL_UNSIGNED_INT_IMAGE_2D_MULTISAMPLE, GL_UNSIGNED_INT_IMAGE_2D_MULTISAMPLE_ARRAY, and the atomic counter type, GL_UNSIGNED_INT_ATOMIC_COUNTER are only available if the GL version is 4.2 or higher.

                                .SH "ERRORS"
                                .PP GL_INVALID_VALUE is generated if program is not a value generated by OpenGL.
                                .PP GL_INVALID_OPERATION is generated if program is not a program object.
                                .PP GL_INVALID_VALUE is generated if index is greater than or equal to the number of active uniform variables in program.
                                .PP GL_INVALID_VALUE is generated if bufSize is less than 0.

                                .SH "ASSOCIATED GETS"
                                .PP glGet() with argument GL_MAX_VERTEX_UNIFORM_COMPONENTS, GL_MAX_GEOMETRY_UNIFORM_COMPONENTS, GL_MAX_TESS_CONTROL_UNIFORM_COMPONENTS, GL_MAX_TESS_EVALUATION_UNIFORM_COMPONENTS, GL_MAX_FRAGMENT_UNIFORM_COMPONENTS.
                                .PP glGetProgram() with argument GL_ACTIVE_UNIFORMS or GL_ACTIVE_UNIFORM_MAX_LENGTH.
                                .PP glIsProgram()

                                .SH "VERSION SUPPORT"
                                    .TS allbox tab(:); lB cB s s s s s s s s s s s lB cB cB cB cB cB cB cB cB cB cB cB cB. T{ T}:T{ OpenGL Version T} T{ Function / Feature Name T}:T{ 2.0 T}:T{ 2.1 T}:T{ 3.0 T}:T{ 3.1 T}:T{ 3.2 T}:T{ 3.3 T}:T{ 4.0 T}:T{ 4.1 T}:T{ 4.2 T}:T{ 4.3 T}:T{ 4.4 T}:T{ 4.5 T} l c c c c c c c c c c c c. T{ glGetActiveUniform T}:T{ ✔ T}:T{ ✔ T}:T{ ✔ T}:T{ ✔ T}:T{ ✔ T}:T{ ✔ T}:T{ ✔ T}:T{ ✔ T}:T{ ✔ T}:T{ ✔ T}:T{ ✔ T}:T{ ✔ T}

                                .SH "SEE ALSO"
                                .PP glGetUniform(), glGetUniformLocation(), glLinkProgram(), glUniform(), glUseProgram()

                                .SH "COPYRIGHT"
                                    .PP Copyright © 2003-2005 3Dlabs Inc. Ltd. Copyright © 2010-2014 Khronos Group This material may be distributed subject to the terms and conditions set forth in the Open Publication License, v 1.0, 8 June 1999. https://opencontent.org/openpub/.

COPYRIGHT
Copyright © 2003-2005 3Dlabs Inc. Ltd.
Copyright © 2010-2014 Khronos Group