glGetActiveUniform — Returns information about an active uniform variable for the specified program object
void glGetActiveUniform(
|
GLuint program, |
| GLuint index, | |
| GLsizei bufSize, | |
| GLsizei *length, | |
| GLint *size, | |
| GLenum *type, | |
GLchar *name); |
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.
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.
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_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.
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.
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.
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.
| OpenGL Version | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Function / Feature Name | 2.0 | 2.1 | 3.0 | 3.1 | 3.2 | 3.3 | 4.0 | 4.1 | 4.2 | 4.3 | 4.4 | 4.5 |
glGetActiveUniform
|
✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ |
glGetUniform, glGetUniformLocation, glLinkProgram, glUniform, glUseProgram
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. http://opencontent.org/openpub/.