Provided by: opengl-4-man-doc_1.0~svn22917-1_all 
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