Parameters

Description

glUniform modifies the value of a uniform variable or a uniform variable array. The location of the uniform variable to be modified is specified by location, which should be a value returned by glGetUniformLocation. glUniform operates on the program object that was made part of current state by calling glUseProgram.

The commands glUniform{1|2|3|4}{f|i|ui} are used to change the value of the uniform variable specified by location using the values passed as arguments. The number specified in the command should match the number of components in the data type of the specified uniform variable (e.g., 1 for float, int, unsigned int, bool; 2 for vec2, ivec2, uvec2, bvec2, etc.). The suffix f indicates that floating-point values are being passed; the suffix i indicates that integer values are being passed; the suffix ui indicates that unsigned integer values are being passed, and this type should also match the data type of the specified uniform variable. The i variants of this function should be used to provide values for uniform variables defined as int, ivec2, ivec3, ivec4, or arrays of these. The ui variants of this function should be used to provide values for uniform variables defined as unsigned int, uvec2, uvec3, uvec4, or arrays of these. The f variants should be used to provide values for uniform variables of type float, vec2, vec3, vec4, or arrays of these. Either the i, ui or f variants may be used to provide values for uniform variables of type bool, bvec2, bvec3, bvec4, or arrays of these. The uniform variable will be set to false if the input value is 0 or 0.0f, and it will be set to true otherwise.

All active uniform variables defined in a program object are initialized to 0 when the program object is linked successfully. They retain the values assigned to them by a call to glUniform until the next successful link operation occurs on the program object, when they are once again initialized to 0.

The commands glUniform{1|2|3|4}{f|i|ui}v can be used to modify a single uniform variable or a uniform variable array. These commands pass a count and a pointer to the values to be loaded into a uniform variable or a uniform variable array. A count of 1 should be used if modifying the value of a single uniform variable, and a count of 1 or greater can be used to modify an entire array or part of an array. When loading n elements starting at an arbitrary position m in a uniform variable array, elements m + n - 1 in the array will be replaced with the new values. If m + n - 1 is larger than the size of the uniform variable array, values for all array elements beyond the end of the array will be ignored. The number specified in the name of the command indicates the number of components for each element in value, and it should match the number of components in the data type of the specified uniform variable (e.g., 1 for float, int, bool; 2 for vec2, ivec2, bvec2, etc.). The data type specified in the name of the command must match the data type for the specified uniform variable as described previously for glUniform{1|2|3|4}{f|i|ui}.

For uniform variable arrays, each element of the array is considered to be of the type indicated in the name of the command (e.g., glUniform3f or glUniform3fv can be used to load a uniform variable array of type vec3). The number of elements of the uniform variable array to be modified is specified by count

The commands glUniformMatrix{2|3|4|2x3|3x2|2x4|4x2|3x4|4x3}fv are used to modify a matrix or an array of matrices. The numbers in the command name are interpreted as the dimensionality of the matrix. The number 2 indicates a 2 × 2 matrix (i.e., 4 values), the number 3 indicates a 3 × 3 matrix (i.e., 9 values), and the number 4 indicates a 4 × 4 matrix (i.e., 16 values). Non-square matrix dimensionality is explicit, with the first number representing the number of columns and the second number representing the number of rows. For example, 2x4 indicates a 2 × 4 matrix with 2 columns and 4 rows (i.e., 8 values). If transpose is GL_FALSE, each matrix is assumed to be supplied in column major order. If transpose is GL_TRUE, each matrix is assumed to be supplied in row major order. The count argument indicates the number of matrices to be passed. A count of 1 should be used if modifying the value of a single matrix, and a count greater than 1 can be used to modify an array of matrices.

Notes

glUniform1i and glUniform1iv are the only two functions that may be used to load uniform variables defined as sampler types. Loading samplers with any other function will result in a GL_INVALID_OPERATION error.

If count is greater than 1 and the indicated uniform variable is not an array, a GL_INVALID_OPERATION error is generated and the specified uniform variable will remain unchanged.

Other than the preceding exceptions, if the type and size of the uniform variable as defined in the shader do not match the type and size specified in the name of the command used to load its value, a GL_INVALID_OPERATION error will be generated and the specified uniform variable will remain unchanged.

If location is a value other than -1 and it does not represent a valid uniform variable location in the current program object, an error will be generated, and no changes will be made to the uniform variable storage of the current program object. If location is equal to -1, the data passed in will be silently ignored and the specified uniform variable will not be changed.

Errors

GL_INVALID_OPERATION is generated if there is no current program object.

GL_INVALID_OPERATION is generated if the size of the uniform variable declared in the shader does not match the size indicated by the glUniform command.

GL_INVALID_OPERATION is generated if one of the signed or unsigned integer variants of this function is used to load a uniform variable of type float, vec2, vec3, vec4, or an array of these, or if one of the floating-point variants of this function is used to load a uniform variable of type int, ivec2, ivec3, ivec4, unsigned int, uvec2, uvec3, uvec4, or an array of these.

GL_INVALID_OPERATION is generated if one of the signed integer variants of this function is used to load a uniform variable of type unsigned int, uvec2, uvec3, uvec4, or an array of these.

GL_INVALID_OPERATION is generated if one of the unsigned integer variants of this function is used to load a uniform variable of type int, ivec2, ivec3, ivec4, or an array of these.

GL_INVALID_OPERATION is generated if location is an invalid uniform location for the current program object and location is not equal to -1.

GL_INVALID_VALUE is generated if count is less than 0.

GL_INVALID_OPERATION is generated if count is greater than 1 and the indicated uniform variable is not an array variable.

GL_INVALID_OPERATION is generated if a sampler is loaded using a command other than glUniform1i and glUniform1iv.

Associated Gets

glGet with the argument GL_CURRENT_PROGRAM

glGetActiveUniform with the handle of a program object and the index of an active uniform variable

glGetUniform with the handle of a program object and the location of a uniform variable

glGetUniformLocation with the handle of a program object and the name of a uniform variable

Tutorials

open.gl - Textures Objects and Parameters
open.gl - Transformations
opengl-tutorial.org - Tutorial 13 : Normal Mapping
opengl-tutorial.org - Tutorial 16 : Shadow mapping
opengl-tutorial.org - Tutorial 3 : Matrices

Version Support

See Also

glLinkProgram, glUseProgram

Copyright

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. https://opencontent.org/openpub/.