GLAPI/glGetActiveUniform

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glGetActiveUniform
Core in version 4.5
Core since version 2.0

glGetActiveUniform: Returns information about an active uniform variable for the specified program object

Function Definition

 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. This is not a uniform location.
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 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


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.

glGetUniformIndices

glGetProgramInterface with GL_UNIFORM and either GL_ACTIVE_RESOURCES or GL_MAX_NAME_LENGTH

See Also

glGetActiveUniforms, glGetActiveUniformName, glGetProgramResource, glGetProgramResourceName

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/.