WebGLRenderingContext.viewport

The WebGLRenderingContext.viewport() method of the WebGL API sets the viewport, which specifies the affine transformation of x and y from normalized device coordinates to window coordinates.

Syntax

void gl.viewport(x, y, width, height);

Parameters

x

A GLint specifying the horizontal coordinate for the lower left corner of the viewport origin. Default value: 0.

y

A GLint specifying the vertical coordinate for the lower left corner of the viewport origin. Default value: 0.

width

A non-negative Glsizei specifying the width of the viewport. Default value: width of the canvas.

height

A non-negative Glsizei specifying the height of the viewport. Default value: height of the canvas.

Return value

None.

Errors thrown

If either width or height is a negative value, a gl.INVALID_VALUE error is thrown.

Examples

When you first create a WebGL context, the size of the viewport will match the size of the canvas. However, if you resize the canvas, you will need to tell the WebGL context a new viewport setting. In this situation, you can use gl.viewport.

gl.viewport(0, 0, canvas.width, canvas.height);

The viewport width and height are clamped to a range that is implementation dependent. To get this range, you can use the MAX_VIEWPORT_DIMS constant, which returns an Int32Array.

gl.getParameter(gl.MAX_VIEWPORT_DIMS);
// e.g. Int32Array[16384, 16384]

To get the current viewport, query the VIEWPORT constant.

gl.getParameter(gl.VIEWPORT);
// e.g. Int32Array[0, 0, 640, 480]

Specifications

Specification	Status	Comment
WebGL 1.0 The definition of 'viewport' in that specification.	Recommendation	Initial definition.
OpenGL ES 2.0 The definition of 'glViewport' in that specification.	Standard	Man page of the OpenGL API.

Browser compatibility

See also

• WebGLRenderingContext.scissor()
• WebGLRenderingContext.getParameter()