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NAME
glGetActiveUniform - Returns information about an active uniform variable for the specified program
object
C SPECIFICATION
void glGetActiveUniform(GLuint program, GLuint index, GLsizei bufSize, GLsizei *length, GLint *size,
GLenum *type, GLchar *name);
PARAMETERS
program
Specifies the program object to be queried.
index
Specifies the index of the uniform variable to be queried.
bufSize
Specifies the maximum number of characters OpenGL is allowed to write in the character buffer
indicated by name.
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.
size
Returns the size of the uniform variable.
type
Returns the data type of the uniform variable.
name
Returns a null terminated string containing the name of the uniform variable.
DESCRIPTION
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 │ Shader │
│ Symbolic Contant │ 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 │
└──────────────────────────────────────────────┴────────────────────────────────┘
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.
NOTES
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.
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.
ERRORS
GL_INVALID_VALUE is generated if program is not a value generated by OpenGL.
GL_INVALID_OPERATION is generated if program is not a program object.
GL_INVALID_VALUE is generated if index is greater than or equal to the number of active uniform variables
in program.
GL_INVALID_VALUE is generated if bufSize is less than 0.
ASSOCIATED GETS
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.
glGetProgram() with argument GL_ACTIVE_UNIFORMS or GL_ACTIVE_UNIFORM_MAX_LENGTH.
glIsProgram()
SEE ALSO
glGetUniform(), glGetUniformLocation(), glLinkProgram(), glUniform(), glUseProgram()
COPYRIGHT
Copyright © 2003-2005 3Dlabs Inc. Ltd. Copyright © 2010 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.
http://opencontent.org/openpub/.
AUTHORS
opengl.org
opengl.org 10/22/2013 GLGETACTIVEUNIFORM(3G)