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docs.GL

glGetUniform

Name

glGetUniform — Returns the value of a uniform variable

C Specification

void glGetUniformfv( GLuint program,
  GLint location,
  GLfloat *params);
 
void glGetUniformiv( GLuint program,
  GLint location,
  GLint *params);
 
void glGetUniformuiv( GLuint program,
  GLint location,
  GLuint *params);
 
void glGetnUniformfv( GLuint program,
  GLint location,
  GLsizei bufSize,
  GLfloat *params);
 
void glGetnUniformiv( GLuint program,
  GLint location,
  GLsizei bufSize,
  GLint *params);
 
void glGetnUniformuiv( GLuint program,
  GLint location,
  GLsizei bufSize,
  GLuint *params);
 

Parameters

program

Specifies the program object to be queried.

location

Specifies the location of the uniform variable to be queried.

bufSize

Specifies the size of the buffer params.

params

Returns the value of the specified uniform variable.

Description

glGetUniform and glGetnUniform return in params the value(s) of the specified uniform variable. The type of the uniform variable specified by location determines the number of values returned. If the uniform variable is defined in the shader as a boolean, int, unsigned int, or float, a single value will be returned. If it is defined as a vec2, ivec2, uvec2, or bvec2, two values will be returned. If it is defined as a vec3, ivec3, uvec3, or bvec3, three values will be returned, and so on. To query values stored in uniform variables declared as arrays, call glGetUniform for each element of the array. To query values stored in uniform variables declared as structures, call glGetUniform for each field in the structure. The values for uniform variables declared as a matrix will be returned in column major order.

The locations assigned to uniform variables are not known until the program object is linked. After linking has occurred, the command glGetUniformLocation can be used to obtain the location of a uniform variable. This location value can then be passed to glGetUniform or glGetnUniform in order to query the current value of the uniform variable. After a program object has been linked successfully, the index values for uniform variables remain fixed until the next link command occurs. The uniform variable values can only be queried after a link if the link was successful.

The only difference between glGetUniform and glGetnUniform is that glGetnUniform will generate an error if size of the params buffer, as described by bufSize, is not large enough to hold the result data.

Notes

If an error is generated, no change is made to the contents of params.

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_OPERATION is generated if program has not been successfully linked.

GL_INVALID_OPERATION is generated if location does not correspond to a valid uniform variable location for the specified program object.

GL_INVALID_OPERATION is generated by glGetnUniform if the buffer size required to store the requested data is greater than bufSize.

Associated Gets

glGetActiveUniform with arguments program and the index of an active uniform variable

glGetProgramiv with arguments program and GL_ACTIVE_UNIFORMS or GL_ACTIVE_UNIFORM_MAX_LENGTH

glGetUniformLocation with arguments program and the name of a uniform variable

API Version Support

OpenGL ES API Version
Function Name 2.0 3.0 3.1 3.2
glGetUniformfv ✔ ✔ ✔ ✔
glGetUniformiv ✔ ✔ ✔ ✔
glGetUniformuiv - ✔ ✔ ✔
glGetnUniformfv - - - ✔
glGetnUniformiv - - - ✔
glGetnUniformuiv - - - ✔
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