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.

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.

None (undefined).

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

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]

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