glGetActiveUniform : PyOpenGL 3.1.4 GL Man Pages

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

Signature

glGetActiveUniform( GLuint ( program ) , GLuint ( index ) , GLsizei ( bufSize ) , GLsizei *( length ) , GLint *( size ) , GLenum *( type ) , GLchar *( name ) )-> void

glGetActiveUniform( program , index , bufSize , length , size , type , name )

Retrieve the name, size and type of the uniform of the index in the program
    
    program -- specifies the program to be queried
    index -- index of the uniform to be queried 
    
    Following parameters are optional:
    
    bufSize -- determines the size of the buffer (limits number of bytes written),
               if not provided, will be GL_OBJECT_ACTIVE_UNIFORM_MAX_LENGTH
    length -- pointer-to-GLsizei that will hold the resulting length of the name
    size -- pointer-to-GLint that will hold the size of the attribute
    type -- pointer-to-GLenum that will hold the type constant of the attribute
    name -- pointer-to-GLchar that will hold the (null-terminated) name string
    
    returns (bytes) name, (int)size, (enum)type

glGetActiveUniformsiv( program , uniformCount , uniformIndices , pname , params )

Parameters

Variables	Description
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 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.

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

Version Support

glGetActiveUniform

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.

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