2.0 3.0 > comp > gb.opengl > gl > viewport
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Gl.Viewport (gb.opengl)
`STATIC SUB Viewport ( X AS Integer, Y AS Integer, Width AS Integer, Height AS Integer )`

Set the viewport.

### Parameters

x, y

Specify the lower left corner of the viewport rectangle, in pixels. The initial value is (0,0).

width, height

Specify the width and height of the viewport. When a GL context is first attached to a window, width and height are set to the dimensions of that window.

### Description

Gl.Viewport specifies the affine transformation of $\mathit{x}$ and $\mathit{y}$ from normalized device coordinates to window coordinates. Let $\left({\mathit{x}}_{\mathit{nd}},{\mathit{y}}_{\mathit{nd}}\right)$ be normalized device coordinates. Then the window coordinates $\left({\mathit{x}}_{\mathit{w}},{\mathit{y}}_{\mathit{w}}\right)$ are computed as follows:

${\mathit{x}}_{\mathit{w}}=\left({\mathit{x}}_{\mathit{nd}}+1\right)\left(\frac{\mathit{width}}{2}\right)+\mathit{x}$

${\mathit{y}}_{\mathit{w}}=\left({\mathit{y}}_{\mathit{nd}}+1\right)\left(\frac{\mathit{height}}{2}\right)+\mathit{y}$

Viewport width and height are silently clamped to a range that depends on the implementation. To query this range, call Gl.Get with argument Gl.MAX_VIEWPORT_DIMS.

### Errors

Gl.INVALID_VALUE is generated if either width or height is negative.

### Associated Gets

Gl.Get with argument Gl.VIEWPORT

Gl.Get with argument Gl.MAX_VIEWPORT_DIMS