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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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