WebGLRenderingContext: viewport() method

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

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

viewport(x, y, width, height)

Parameters

• x
  • : A {{domxref("WebGL_API/Types", "GLint")}} specifying the horizontal coordinate for the lower left corner of the viewport origin. Default value: 0.
• y
  • : A {{domxref("WebGL_API/Types", "GLint")}} specifying the vertical coordinate for the lower left corner of the viewport origin. Default value: 0.
• width
  • : A non-negative {{domxref("WebGL_API/Types", "GLsizei")}} specifying the width of the viewport. Default value: width of the canvas.
• height
  • : A non-negative {{domxref("WebGL_API/Types", "GLsizei")}} specifying the height of the viewport. Default value: height of the canvas.

Return value

None ({{jsxref("undefined")}}).

Exceptions

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 {{jsxref("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

{{Specifications}}

Browser compatibility

{{Compat}}

See also

• {{domxref("WebGLRenderingContext.scissor()")}}
• {{domxref("WebGLRenderingContext.getParameter()")}}