Constructs a new shader program and attaches it to parent. The program will be invalid until addShader() is called. The shader program will be associated with the current QOpenGLContext.

Deletes this QOpenGLShaderProgram.

Adds a compiled shader to this shader program. Returns true if the shader could be added, otherwise returns false. Ownership of the shader object remains with the caller. It will not be deleted when this QOpenGLShaderProgram instance is deleted. This allows the caller to add the same shader to multiple shader programs.

See also

addShaderFromSourceCode(), addShaderFromSourceFile(), link(), removeShader(), removeAllShaders()

Compiles source as a shader of the specified type and adds it to this shader program. Returns true if compilation was successful, otherwise returns false. The compilation errors and warnings will be made available via log().

This method is a shortcut to add a vertex or fragment shader to a shader program without needing to create a QOpenGLShader.

See also

addShader(), addShaderFromSourceFile(), link(), removeShader(), removeAllShaders()

Compiles source as a shader of the specified type and adds it to this shader program. Returns true if compilation was successful, otherwise returns false. The compilation errors and warnings will be made available via log().

This method is a shortcut to add a vertex or fragment shader to a shader program without needing to create a QOpenGLShader.

See also

addShader(), addShaderFromSourceFile(), link(), removeShader(), removeAllShaders()

Compiles source as a shader of the specified type and adds it to this shader program. Returns true if compilation was successful, otherwise returns false. The compilation errors and warnings will be made available via log().

This method is a shortcut to add a vertex or fragment shader to a shader program without needing to create a QOpenGLShader.

See also

addShader(), addShaderFromSourceFile(), link(), removeShader(), removeAllShaders()

Compiles the contents of fileName as a shader of the specified type and adds it to this shader program. Returns true if compilation was successful, otherwise returns false. The compilation errors and warnings will be made available via log().

This method is a shortcut to add a vertex or fragment shader to a shader program without needing to create a QOpenGLShader.

See also

addShader(), addShaderFromSourceCode()

Returns the position of the attribute with the given name. A return value of -1 indicates the name is not a valid attribute for this shader program.

See also

bindAttributeLocation(), uniformLocation()

Returns the position of the attribute with the given name. A return value of -1 indicates the name is not a valid attribute for this shader program.

See also

bindAttributeLocation(), uniformLocation()

Returns the position of the attribute with the given name. A return value of -1 indicates the name is not a valid attribute for this shader program.

See also

bindAttributeLocation(), uniformLocation()

Binds this QOpenGLShaderProgram to the active QOpenGLContext. The shader program becomes active and is used for rendering. Any previously bound shader program is released. Returns true if the program was successfully bound, otherwise false is returned.

If the shader program has not been linked or it needs to be relinked this method will automatically call link().

Equivalent to calling glUseProgram() and passing the programId().

See also

release()

Binds the attribute name to the specified location. This method can be called before or after the program has been linked. Any attributes that have not been explicitly bound when the program is linked will be assigned locations automatically.

If this method is called after the shader program has been linked the shader program will need to be relinked.

See also

attributeLocation()

Binds the attribute name to the specified location. This method can be called before or after the program has been linked. Any attributes that have not been explicitly bound when the program is linked will be assigned locations automatically.

If this method is called after the shader program has been linked the shader program will need to be relinked.

See also

attributeLocation()

Binds the attribute name to the specified location. This method can be called before or after the program has been linked. Any attributes that have not been explicitly bound when the program is linked will be assigned locations automatically.

If this method is called after the shader program has been linked the shader program will need to be relinked.

See also

attributeLocation()

Requests the shader program's id to be created immediately. Returns true if successful, otherwise returns false. This method is primarily useful when combining QOpenGLShaderProgram with other OpenGL functions that operate directly on the shader program id, like GL_OES_get_program_binary.

When the shader program is used normally, the shader program's id will be created on demand.

See also

programId()

Returns a QVector of floats describing the inner tessellation levels. The vector will always have two elements but not all of them may be used for every mode of tessellation. These default inner tessellation levels will be used by the tessellation primitive generator if the tessellation control shader does not provide any.

Note

This method is only supported with OpenGL >= 4.0 and will not return valid results with OpenGL ES 3.2.

See also

defaultOuterTessellationLevels(), setDefaultInnerTessellationLevels()

Returns a QVector of floats describing the outer tessellation levels. The vector will always have two elements but not all of them may be used for every mode of tessellation. These default outer tessellation levels will be used by the tessellation primitive generator if the tessellation control shader does not provide any.

Note

This method is only supported with OpenGL >= 4.0 and will not return valid results with OpenGL ES 3.2.

See also

defaultInnerTessellationLevels(), setDefaultOuterTessellationLevels()

Disables the vertex array called name in this shader program that was enabled by a previous call to enableAttributeArray().

See also

enableAttributeArray(), setAttributeArray(), setAttributeValue(), setUniformValue()

Disables the vertex array at location in this shader program that was enabled by a previous call to enableAttributeArray().

See also

enableAttributeArray(), setAttributeArray(), setAttributeValue(), setUniformValue()

Enables the vertex array called name in this shader program so that the value set by setAttributeArray() on name will be used by the shader program.

See also

disableAttributeArray(), setAttributeArray(), setAttributeValue(), setUniformValue()

Enables the vertex array at location in this shader program so that the value set by setAttributeArray() on location will be used by the shader program.

See also

disableAttributeArray(), setAttributeArray(), setAttributeValue(), setUniformValue()

The context is used to resolve the GLSL extensions. If context is nullptr, then QOpenGLContext::currentContext() is used. Returns true if shader programs written in the OpenGL Shading Language (GLSL) are supported on this system, otherwise false is returned.

Returns true if this shader program has been linked, otherwise false is returned.

See also

link()

Links together the shaders that were added to this program with addShader(). Returns true if the link was successful or otherwise returns false. If the link failed, the error messages can be retrieved with log(). Subclasses can override this method to initialize attributes and uniform variables for use in specific shader programs.

If the shader program was already linked, calling this method again will force it to be relinked.

When shaders were added to this program via addCacheableShaderFromSourceCode() or addCacheableShaderFromSourceFile(), program binaries are supported, and a cached binary is available on disk, actual compilation and linking are skipped. Instead, this method will initialize the program with the binary blob via glProgramBinary(). If there is no cached version of the program or it was generated with a different driver version, the shaders will be compiled from source and the program will get linked normally. This allows seamless upgrading of the graphics drivers, without having to worry about potentially incompatible binary formats.

Returns the errors and warnings that occurred during the last link() or addShader() with explicitly specified source code.

Returns the hardware limit for how many vertices a geometry shader can output.

Returns the number of vertices per patch to be used when rendering.

See also

setPatchVertexCount()

Returns the OpenGL identifier associated with this shader program.

Releases the active shader program from the current QOpenGLContext. This is equivalent to calling glUseProgram(0).

See also

bind()

Removes all of the shaders that were added to this program previously. The QOpenGLShader objects for the shaders will not be deleted if they were constructed externally. QOpenGLShader objects that are constructed internally by QOpenGLShaderProgram will be deleted.

See also

addShader(), removeShader()

Removes shader from this shader program. The object is not deleted. The shader program must be valid in the current QOpenGLContext.

See also

addShader(), link(), removeAllShaders()

Sets an array of vertex values on the attribute called name in this shader program. The tupleSize indicates the number of components per vertex (1, 2, 3, or 4), and the stride indicates the number of bytes between vertices. A default stride value of zero indicates that the vertices are densely packed in values.

The array will become active when enableAttributeArray() is called on name. Otherwise the value specified with setAttributeValue() for name will be used.

See also

disableAttributeArray(), enableAttributeArray(), setAttributeValue(), setUniformValue()

Sets an array of 2D vertex values on the attribute called name in this shader program. The stride indicates the number of bytes between vertices. A default stride value of zero indicates that the vertices are densely packed in values.

The array will become active when enableAttributeArray() is called on name. Otherwise the value specified with setAttributeValue() for name will be used.

See also

disableAttributeArray(), enableAttributeArray(), setAttributeValue(), setUniformValue()

Sets an array of 3D vertex values on the attribute called name in this shader program. The stride indicates the number of bytes between vertices. A default stride value of zero indicates that the vertices are densely packed in values.

The array will become active when enableAttributeArray() is called on name. Otherwise the value specified with setAttributeValue() for name will be used.

See also

disableAttributeArray(), enableAttributeArray(), setAttributeValue(), setUniformValue()

Sets an array of 4D vertex values on the attribute called name in this shader program. The stride indicates the number of bytes between vertices. A default stride value of zero indicates that the vertices are densely packed in values.

The array will become active when enableAttributeArray() is called on name. Otherwise the value specified with setAttributeValue() for name will be used.

See also

disableAttributeArray(), enableAttributeArray(), setAttributeValue(), setUniformValue()

Sets an array of vertex values on the attribute called name in this shader program. The stride indicates the number of bytes between vertices. A default stride value of zero indicates that the vertices are densely packed in values.

The type indicates the type of elements in the values array, usually GL_FLOAT, GL_UNSIGNED_BYTE, etc. The tupleSize indicates the number of components per vertex: 1, 2, 3, or 4.

The array will become active when enableAttributeArray() is called on the name. Otherwise the value specified with setAttributeValue() for name will be used. The setAttributeBuffer() method can be used to set the attribute array to an offset within a vertex buffer.

See also

disableAttributeArray(), enableAttributeArray(), setAttributeValue(), setAttributeBuffer(), setUniformValue()

Sets an array of vertex values on the attribute at location in this shader program. The tupleSize indicates the number of components per vertex (1, 2, 3, or 4), and the stride indicates the number of bytes between vertices. A default stride value of zero indicates that the vertices are densely packed in values.

The array will become active when enableAttributeArray() is called on the location. Otherwise the value specified with setAttributeValue() for location will be used.

See also

disableAttributeArray(), enableAttributeArray(), setAttributeValue(), setUniformValue()

Sets an array of 2D vertex values on the attribute at location in this shader program. The stride indicates the number of bytes between vertices. A default stride value of zero indicates that the vertices are densely packed in values.

The array will become active when enableAttributeArray() is called on the location. Otherwise the value specified with setAttributeValue() for location will be used.

See also

disableAttributeArray(), enableAttributeArray(), setAttributeValue(), setUniformValue()

Sets an array of 3D vertex values on the attribute at location in this shader program. The stride indicates the number of bytes between vertices. A default stride value of zero indicates that the vertices are densely packed in values.

The array will become active when enableAttributeArray() is called on the location. Otherwise the value specified with setAttributeValue() for location will be used.

See also

disableAttributeArray(), enableAttributeArray(), setAttributeValue(), setUniformValue()

Sets an array of 4D vertex values on the attribute at location in this shader program. The stride indicates the number of bytes between vertices. A default stride value of zero indicates that the vertices are densely packed in values.

The array will become active when enableAttributeArray() is called on the location. Otherwise the value specified with setAttributeValue() for location will be used.

See also

disableAttributeArray(), enableAttributeArray(), setAttributeValue(), setUniformValue()

Sets an array of vertex values on the attribute at location in this shader program. The stride indicates the number of bytes between vertices. A default stride value of zero indicates that the vertices are densely packed in values.

The type indicates the type of elements in the values array, usually GL_FLOAT, GL_UNSIGNED_BYTE, etc. The tupleSize indicates the number of components per vertex: 1, 2, 3, or 4.

The array will become active when enableAttributeArray() is called on the location. Otherwise the value specified with setAttributeValue() for location will be used. The setAttributeBuffer() method can be used to set the attribute array to an offset within a vertex buffer.

Normalization will be enabled. If this is not desired, call glVertexAttribPointer directly through QOpenGLFunctions.

See also

disableAttributeArray(), enableAttributeArray(), setAttributeValue(), setAttributeBuffer(), setUniformValue()

Sets an array of vertex values on the attribute called name in this shader program, starting at a specific offset in the currently bound vertex buffer. The stride indicates the number of bytes between vertices. A default stride value of zero indicates that the vertices are densely packed in the value array.

The type indicates the type of elements in the vertex value array, usually GL_FLOAT, GL_UNSIGNED_BYTE, etc. The tupleSize indicates the number of components per vertex: 1, 2, 3, or 4.

The array will become active when enableAttributeArray() is called on the name. Otherwise the value specified with setAttributeValue() for name will be used.

Sets an array of vertex values on the attribute at location in this shader program, starting at a specific offset in the currently bound vertex buffer. The stride indicates the number of bytes between vertices. A default stride value of zero indicates that the vertices are densely packed in the value array.

The type indicates the type of elements in the vertex value array, usually GL_FLOAT, GL_UNSIGNED_BYTE, etc. The tupleSize indicates the number of components per vertex: 1, 2, 3, or 4.

The array will become active when enableAttributeArray() is called on the location. Otherwise the value specified with setAttributeValue() for location will be used.

Normalization will be enabled. If this is not desired, call glVertexAttribPointer directly through QOpenGLFunctions.

Sets the attribute called name in the current context to the contents of values, which contains columns elements, each consisting of rows elements. The rows value should be 1, 2, 3, or 4. This method is typically used to set matrix values and column vectors.

Sets the attribute called name in the current context to value.

Sets the attribute called name in the current context to value.

Sets the attribute called name in the current context to value.

Sets the attribute called name in the current context to value.

Sets the attribute called name in the current context to value.

Sets the attribute called name in the current context to the 2D vector (x, y).

Sets the attribute called name in the current context to the 3D vector (x, y, z).

Sets the attribute called name in the current context to the 4D vector (x, y, z, w).

Sets the attribute at location in the current context to the contents of values, which contains columns elements, each consisting of rows elements. The rows value should be 1, 2, 3, or 4. This method is typically used to set matrix values and column vectors.

Sets the attribute at location in the current context to value.

Sets the attribute at location in the current context to value.

Sets the attribute at location in the current context to value.

Sets the attribute at location in the current context to value.

Sets the attribute at location in the current context to value.

Sets the attribute at location in the current context to the 2D vector (x, y).

Sets the attribute at location in the current context to the 3D vector (x, y, z).

Sets the attribute at location in the current context to the 4D vector (x, y, z, w).

Sets the default outer tessellation levels to be used by the tessellation primitive generator in the event that the tessellation control shader does not output them to levels. For more details on OpenGL and Tessellation shaders see OpenGL Tessellation Shaders.

The levels argument should be a QVector consisting of 2 floats. Not all of the values make sense for all tessellation modes. If you specify a vector with fewer than 2 elements, the remaining elements will be given a default value of 1.

Calling this method will modify the global OpenGL state and the values are not isolated to this specific QOpenGLShaderProgram instance.

Note

This method is only available with OpenGL >= 4.0 and is not supported with OpenGL ES 3.2.

See also

defaultInnerTessellationLevels(), setDefaultOuterTessellationLevels()

Sets the default outer tessellation levels to be used by the tessellation primitive generator in the event that the tessellation control shader does not output them to levels. For more details on OpenGL and Tessellation shaders see OpenGL Tessellation Shaders.

The levels argument should be a QVector consisting of 4 floats. Not all of the values make sense for all tessellation modes. If you specify a vector with fewer than 4 elements, the remaining elements will be given a default value of 1.

Calling this method will modify the global OpenGL state and the values are not isolated to this specific QOpenGLShaderProgram instance.

Note

This method is only available with OpenGL >= 4.0 and is not supported with OpenGL ES 3.2.

See also

defaultOuterTessellationLevels(), setDefaultInnerTessellationLevels()

Use this method to specify to OpenGL the number of vertices in a patch to count. A patch is a custom OpenGL primitive whose interpretation is entirely defined by the tessellation shader stages. Therefore, calling this method only makes sense when using a QOpenGLShaderProgram containing tessellation stage shaders. When using OpenGL tessellation, the only primitive that can be rendered with glDraw*() functions is GL_PATCHES.

Equivalent to calling glPatchParameteri(GL_PATCH_VERTICES, count).

Calling this method will modify the global OpenGL state and the values are not isolated to this specific QOpenGLShaderProgram instance.

See also

patchVertexCount()

Sets the uniform variable called name in the current context to a 2x2 matrix value. The matrix elements must be specified in column-major order.

Sets the uniform variable called name in the current context to a 3x3 matrix value. The matrix elements must be specified in column-major order.

Sets the uniform variable called name in the current context to a 4x4 matrix value. The matrix elements must be specified in column-major order.

Sets the uniform variable called name in the current context to the red, green, blue, and alpha components of color.

Sets the uniform variable called name in the current context to a 2x2 matrix value.

Sets the uniform variable called name in the current context to a 2x3 matrix value.

This method is not aware of non square matrix support for GLSL types like mat2x3 which are present in modern OpenGL versions. Instead, it treats the uniform as an array of vec3.

Sets the uniform variable called name in the current context to a 2x4 matrix value.

This method is not aware of non square matrix support for GLSL types like mat2x4 which are present in modern OpenGL versions. Instead, it treats the uniform as an array of vec4.

Sets the uniform variable called name in the current context to a 3x2 matrix value.

This method is not aware of non square matrix support for GLSL types like mat3x2 which are present in modern OpenGL versions. Instead, it treats the uniform as an array of vec2.

Sets the uniform variable called name in the current context to a 3x3 matrix value.

Sets the uniform variable called name in the current context to a 3x4 matrix value.

This method is not aware of non square matrix support for GLSL types like mat3x4 which are present in modern OpenGL versions. Instead, it treats the uniform as an array of vec4.

Sets the uniform variable called name in the current context to a 4x2 matrix value.

This method is not aware of non square matrix support for GLSL types like mat4x2 which are present in modern OpenGL versions. Instead, it treats the uniform as an array of vec2.

Sets the uniform variable called name in the current context to a 4x3 matrix value.

This method is not aware of non square matrix support for GLSL types like mat4x3 which are present in modern OpenGL versions. Instead, it treats the uniform as an array of vec3.

Sets the uniform variable called name in the current context to a 4x4 matrix value.

Sets the uniform variable associated with name in the current context to the x and y coordinates of point.

Sets the uniform variable associated with name in the current context to the x and y coordinates of point.

Sets the uniform variable associated with name in the current context to the width and height of the given size.

Sets the uniform variable associated with name in the current context to the width and height of the given size.

Sets the uniform variable called name in the current context to a 3x3 transformation matrix value that is specified as a QTransform value.

To set a QTransform value as a 4x4 matrix in a shader, use setUniformValue(name, QMatrix4x4(value)).

Sets the uniform variable called name in the current context to value.

Sets the uniform variable called name in the current context to value.

Sets the uniform variable called name in the current context to value.

Sets the uniform variable called name in the current context to value.

Sets the uniform variable called name in the current context to the 2D vector (x, y).

Sets the uniform variable called name in the current context to the 3D vector (x, y, z).

Sets the uniform variable called name in the current context to the 4D vector (x, y, z, w).

Sets the uniform variable called name in the current context to value.

Sets the uniform variable called name in the current context to value.

This method is not aware of unsigned int support in modern OpenGL versions and therefore treats value as a GLint and calls glUniform1i.

Sets the uniform variable at location in the current context to a 2x2 matrix value. The matrix elements must be specified in column-major order.

Sets the uniform variable at location in the current context to a 3x3 matrix value. The matrix elements must be specified in column-major order.

Sets the uniform variable at location in the current context to a 4x4 matrix value. The matrix elements must be specified in column-major order.

Sets the uniform variable at location in the current context to the red, green, blue, and alpha components of color.

Sets the uniform variable at location in the current context to a 2x2 matrix value.

Sets the uniform variable at location in the current context to a 2x3 matrix value.

This method is not aware of non square matrix support for GLSL types like mat2x3 which are present in modern OpenGL versions. Instead, it treats the uniform as an array of vec3.

Sets the uniform variable at location in the current context to a 2x4 matrix value.

This method is not aware of non square matrix support for GLSL types like mat2x4 which are present in modern OpenGL versions. Instead, it treats the uniform as an array of vec4.

Sets the uniform variable at location in the current context to a 3x2 matrix value.

This method is not aware of non square matrix support for GLSL types like mat3x2 which are present in modern OpenGL versions. Instead, it treats the uniform as an array of vec2.

Sets the uniform variable at location in the current context to a 3x3 matrix value.

Sets the uniform variable at location in the current context to a 3x4 matrix value.

This method is not aware of non square matrix support for GLSL types like mat3x4 which are present in modern OpenGL versions. Instead, it treats the uniform as an array of vec4.

Sets the uniform variable at location in the current context to a 4x2 matrix value.

This method is not aware of non square matrix support for GLSL types like mat4x2 which are present in modern OpenGL versions. Instead, it treats the uniform as an array of vec2.

Sets the uniform variable at location in the current context to a 4x3 matrix value.

This method is not aware of non square matrix support for GLSL types like mat4x3 which are present in modern OpenGL versions. Instead, it treats the uniform as an array of vec3.

Sets the uniform variable at location in the current context to a 4x4 matrix value.

Sets the uniform variable at location in the current context to the x and y coordinates of point.

Sets the uniform variable at location in the current context to the x and y coordinates of point.

Sets the uniform variable at location in the current context to the width and height of the given size.

Sets the uniform variable at location in the current context to the width and height of the given size.

Sets the uniform variable at location in the current context to a 3x3 transformation matrix value that is specified as a QTransform value. To set a QTransform value as a 4x4 matrix in a shader, use setUniformValue(location, QMatrix4x4(value)).

Sets the uniform variable at location in the current context to value.

Sets the uniform variable at location in the current context to value.

Sets the uniform variable at location in the current context to value.

Sets the uniform variable at location in the current context to value.

Sets the uniform variable at location in the current context to the 2D vector (x, y).

Sets the uniform variable at location in the current context to the 3D vector (x, y, z).

Sets the uniform variable at location in the current context to the 4D vector (x, y, z, w).

Sets the uniform variable at location in the current context to value.

Sets the uniform variable at location in the current context to value. This method should be used when setting sampler values.

This method is not aware of unsigned int support in modern OpenGL versions and therefore treats value as a GLint and calls glUniform1i.

Sets the uniform variable array called name in the current context to the count elements of values. Each element has tupleSize components. The tupleSize must be 1, 2, 3, or 4.

Sets the uniform variable array called name in the current context to the count elements of values.

Sets the uniform variable array called name in the current context to the count elements of values.

Sets the uniform variable array called name in the current context to the count 2x2 matrix elements of values.

Sets the uniform variable array called name in the current context to the count 2x3 matrix elements of values.

Sets the uniform variable array called name in the current context to the count 2x4 matrix elements of values.

Sets the uniform variable array called name in the current context to the count 3x2 matrix elements of values.

Sets the uniform variable array called name in the current context to the count 3x3 matrix elements of values.

Sets the uniform variable array called name in the current context to the count 3x4 matrix elements of values.

Sets the uniform variable array called name in the current context to the count 4x2 matrix elements of values.

Sets the uniform variable array called name in the current context to the count 4x3 matrix elements of values.

Sets the uniform variable array called name in the current context to the count 4x4 matrix elements of values.

Sets the uniform variable array called name in the current context to the count 2D vector elements of values.

Sets the uniform variable array called name in the current context to the count 3D vector elements of values.

Sets the uniform variable array called name in the current context to the count 4D vector elements of values.

Sets the uniform variable array at location in the current context to the count elements of values. Each element has tupleSize components. The tupleSize must be 1, 2, 3, or 4.

Sets the uniform variable array at location in the current context to the count elements of values.

Sets the uniform variable array at location in the current context to the count elements of values. This overload should be used when setting an array of sampler values.

This method is not aware of unsigned int support in modern OpenGL versions and therefore treats values as a GLint and calls glUniform1iv.

Sets the uniform variable array at location in the current context to the count 2x2 matrix elements of values.

Sets the uniform variable array at location in the current context to the count 2x3 matrix elements of values.

Sets the uniform variable array at location in the current context to the count 2x4 matrix elements of values.

Sets the uniform variable array at location in the current context to the count 3x2 matrix elements of values.

Sets the uniform variable array at location in the current context to the count 3x3 matrix elements of values.

Sets the uniform variable array at location in the current context to the count 3x4 matrix elements of values.

Sets the uniform variable array at location in the current context to the count 4x2 matrix elements of values.

Sets the uniform variable array at location in the current context to the count 4x3 matrix elements of values.

Sets the uniform variable array at location in the current context to the count 4x4 matrix elements of values.

Sets the uniform variable array at location in the current context to the count 2D vector elements of values.

Sets the uniform variable array at location in the current context to the count 3D vector elements of values.

Sets the uniform variable array at location in the current context to the count 4D vector elements of values.

Returns a list of all shaders that have been added to this shader program using addShader().

See also

addShader(), removeShader()

Returns the location of the uniform variable name within this shader program's parameter list. A return value of -1 indicates the name is not a valid uniform variable for this shader program.

Returns the location of the uniform variable name within this shader program's parameter list. A return value of -1 indicates the name is not a valid uniform variable for this shader program.

Returns the location of the uniform variable name within this shader program's parameter list. A return value of -1 indicates the name is not a valid uniform variable for this shader program.