glGetActiveUniform man page on Oracle
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GLGETACTIVEUNIFORM(3G) OpenGL Manual GLGETACTIVEUNIFORM(3G)
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_FRAGMENT_UNIFORM_COMPONENTS,
or GL_MAX_COMBINED_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 04/29/2014 GLGETACTIVEUNIFORM(3G)
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