WebGLRenderingContext: getActiveUniform() method

{{APIRef("WebGL")}}{{AvailableInWorkers}}

The WebGLRenderingContext.getActiveUniform() method of the WebGL API returns a {{domxref("WebGLActiveInfo")}} object containing size, type, and name of a uniform attribute. It is generally used when querying unknown uniforms either for debugging or generic library creation.

Syntax

getActiveUniform(program, index)

Parameters

• program
  • : A {{domxref("WebGLProgram")}} specifying the WebGL shader program from which to obtain the uniform variable's information.
• index
  • : A {{domxref("WebGL_API/Types", "GLuint")}} specifying the index of the uniform attribute to get. This value is an index 0 to N - 1 as returned by {{domxref("WebGLRenderingContext.getProgramParameter", "gl.getProgramParameter(program, gl.ACTIVE_UNIFORMS)")}}.

Return value

A {{domxref("WebGLActiveInfo")}} object describing the uniform.

The type attribute of the return value will be one of the following:

• gl.FLOAT
• gl.FLOAT_VEC2
• gl.FLOAT_VEC3
• gl.FLOAT_VEC4
• gl.INT
• gl.INT_VEC2
• gl.INT_VEC3
• gl.INT_VEC4
• gl.BOOL
• gl.BOOL_VEC2
• gl.BOOL_VEC3
• gl.BOOL_VEC4
• gl.FLOAT_MAT2
• gl.FLOAT_MAT3
• gl.FLOAT_MAT4
• gl.SAMPLER_2D
• gl.SAMPLER_CUBE
• When using a {{domxref("WebGL2RenderingContext", "WebGL 2 context", "", 1)}}, the following values are possible additionally:
  • gl.UNSIGNED_INT
  • gl.UNSIGNED_INT_VEC2
  • gl.UNSIGNED_INT_VEC3
  • gl.UNSIGNED_INT_VEC4
  • gl.FLOAT_MAT2x3
  • gl.FLOAT_MAT2x4
  • gl.FLOAT_MAT3x2
  • gl.FLOAT_MAT3x4
  • gl.FLOAT_MAT4x2
  • gl.FLOAT_MAT4x3
  • gl.SAMPLER_3D
  • gl.SAMPLER_2D_SHADOW
  • gl.SAMPLER_2D_ARRAY
  • gl.SAMPLER_2D_ARRAY_SHADOW
  • gl.SAMPLER_CUBE_SHADOW
  • gl.INT_SAMPLER_2D
  • gl.INT_SAMPLER_3D
  • gl.INT_SAMPLER_CUBE
  • gl.INT_SAMPLER_2D_ARRAY
  • gl.UNSIGNED_INT_SAMPLER_2D
  • gl.UNSIGNED_INT_SAMPLER_3D
  • gl.UNSIGNED_INT_SAMPLER_CUBE
  • gl.UNSIGNED_INT_SAMPLER_2D_ARRAY

When gl.linkProgram is called, WebGL creates a list of active uniforms. These are possible values of the name attribute of return values of getActiveUniform. WebGL generates one or more entries in the list depending on the declared type of the uniform in the shader:

• Single basic type: one entry with the name of the uniform. E.g. uniform vec4 a; will result in a.

• Array of basic type: one entry with the name of the uniform suffixed with [0]. E.g. uniform vec4 b[]; will result in b[0].

• Struct type: one entry for each member of the struct. E.g. uniform struct { float foo; vec4 bar; } c; will result in c.foo and c.bar.

• Arrays of structs or arrays: each entry of the array will generate its own entries. E.g. uniform struct { float foo; vec4 bar; } d[2]; will result in:

  • d[0].foo
  • d[0].bar
  • d[1].foo
  • d[1].bar

• Uniform blocks: one entry for each member. If the uniform block has an instance name, the block name is prefixed. E.g. uniform Block { float foo; }; will result in foo, and uniform Block { float bar; } e; will result in e.bar.

The size attribute of the return value corresponds to the length of the array for uniforms declared as arrays. Otherwise, it is 1 (this includes interface blocks instanced with arrays).

Exceptions

• gl.INVALID_VALUE is generated if the program {{domxref("WebGLProgram")}} is invalid (not linked, deleted, etc.).
• gl.INVALID_VALUE is generated if index is not in the range [0, gl.getProgramParameter(program, gl.ACTIVE_UNIFORMS) - 1].

Examples

const numUniforms = gl.getProgramParameter(program, gl.ACTIVE_UNIFORMS);
for (let i = 0; i < numUniforms; ++i) {
  const info = gl.getActiveUniform(program, i);
  console.log("name:", info.name, "type:", info.type, "size:", info.size);
}

Specifications

{{Specifications}}

Browser compatibility

{{Compat}}

See also

• {{domxref("WebGLActiveInfo")}}
• {{domxref("WebGLRenderingContext.getUniformLocation()")}}