WebGLRenderingContext: getUniformLocation() method
==================================================

 Part of the WebGL API, the `WebGLRenderingContext` method
 **`getUniformLocation()`** returns the location of a
 specific **uniform** variable which is part of a given
 `WebGLProgram`.

 The uniform variable is returned as a
 `WebGLUniformLocation` object, which is an opaque identifier used to
 specify where in the GPU's memory that uniform variable is located.

 Once you have the uniform's location, you can access the uniform itself using one of
 the other uniform access methods, passing in the uniform location as one of the
 inputs:

* `getUniform()`
    + : Returns the value of the uniform at the given location.
* `WebGLRenderingContext.uniform[1234][fi][v]()`
    + : Sets the uniform's value to the specified value, which may be a single floating
     point or integer number, or a 2-4 component vector specified either as a list of
     values or as a `Float32Array` or `Int32Array`.
* `WebGLRenderingContext.uniformMatrix[234][fv]()`
    + : Sets the uniform's value to the specified matrix, possibly with transposition. The
     value is represented as a sequence of `GLfloat` values or as a
     `Float32Array`.

The uniform itself is declared in the shader program using GLSL.

Syntax
------


```js
getUniformLocation(program, name)
```

### Parameters

`program`

The `WebGLProgram` in which to locate the specified uniform variable.

`name`

 A string specifying the name of the uniform variable whose
 location is to be returned. The name can't have any whitespace in it, and you
 can't use this function to get the location of any uniforms starting with the
 reserved string `"gl_"`, since those are internal to the WebGL
 layer.


 The possible values correspond to the uniform names returned by
 `getActiveUniform`; see
 that function for specifics on how declared uniforms map to uniform location
 names.


 Additionally, for uniforms declared as arrays, the following names are also
 valid:


* The uniform name without the `[0]` suffix. E.g. the location
 returned for `arrayUniform` is equivalent to the one for
 `arrayUniform[0]`.
* The uniform name indexed with an integer. E.g. the location returned for
 `arrayUniform[2]` would point directly to the third entry of
 the `arrayUniform` uniform.

### Return value

 A `WebGLUniformLocation` value indicating the location of the named
 variable, if it exists. If the specified variable doesn't exist, `null` is
 returned instead.

 The `WebGLUniformLocation` is an opaque value used to uniquely identify the
 location in the GPU's memory at which the uniform variable is located. With this value
 in hand, you can call other WebGL methods to access the value of the uniform variable.


**Note:** The `WebGLUniformLocation` type is compatible with the
 `GLint` type when specifying the index or location of a uniform
 attribute.


### Errors

 The following errors may occur; to check for errors after
 `getUniformLocation()` returns, call
 `getError()`.

`GL_INVALID_VALUE`

The `program` parameter is not a value or object generated by WebGL.

`GL_INVALID_OPERATION`

 The `program` parameter doesn't correspond to a GLSL program generated
 by WebGL, or the specified program hasn't been linked successfully.


Examples
--------

 In this example, taken from the `animateScene()` method in the article A basic 2D WebGL animation example, obtains the locations of three uniforms from
 the shading program, then sets the value of each of the three uniforms.


```js
gl.useProgram(shaderProgram);

uScalingFactor = gl.getUniformLocation(shaderProgram, "uScalingFactor");
uGlobalColor = gl.getUniformLocation(shaderProgram, "uGlobalColor");
uRotationVector = gl.getUniformLocation(shaderProgram, "uRotationVector");

gl.uniform2fv(uScalingFactor, currentScale);
gl.uniform2fv(uRotationVector, currentRotation);
gl.uniform4fv(uGlobalColor, [0.1, 0.7, 0.2, 1.0]);
```


**Note:** This code snippet is taken from the function `animateScene()` in "A basic 2D WebGL animation example."
 See that article for the full sample and to see the resulting animation in action.


 After setting the current shading program to `shaderProgram`, this code
 fetches the three uniforms `"uScalingFactor"`, `"uGlobalColor"`,
 and `"uRotationVector"`, calling `getUniformLocation()` once for
 each uniform.

Then the three uniforms' values are set:

* The `uScalingFactor` uniform — a 2-component vertex — receives the
 horizontal and vertical scaling factors from the variable
 `currentScale`.
* The uniform `uRotationVector` is set to the contents of the variable
 `currentRotation`. This, too, is a 2-component vertex.
* Finally, the uniform `uGlobalColor` is set to the color
 `[0.1, 0.7, 0.2, 1.0]`, the components in this 4-component vector
 represent the values of red, green, blue, and alpha, respectively.

 Having done this, the next time the shading functions are called, their own variables
 named `uScalingFactor`, `uGlobalColor`, and
 `uRotationVector` will all have the values provided by the JavaScript code.

Specifications
--------------

| Specification |
| --- |
| WebGL Specification # 5.14.10 |

Browser compatibility
---------------------

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See also
--------

* `WebGLRenderingContext.getAttribLocation()`
* `WebGLRenderingContext.getActiveUniform()`
* `WebGLUniformLocation`