# Glu.Perspective (gb.opengl.glu)

Static Sub Perspective ( Fovy As Float, Aspect As Float, ZNear As Float, ZFar As Float )

Set up a perspective projection matrix.

### Parameters

fovy

Specifies the field of view angle, in degrees, in the y direction.
aspect

Specifies the aspect ratio that determines the field of view in the x direction. The aspect ratio is the ratio of x (width) to y (height).
zNear

Specifies the distance from the viewer to the near clipping plane (always positive).
zFar

Specifies the distance from the viewer to the far clipping plane (always positive).

### Description

Glu.Perspective specifies a viewing frustum into the world coordinate system. In general, the aspect ratio in Glu.Perspective should match the aspect ratio of the associated viewport. For example, $\mathit{aspect}2.0$ means the viewer's angle of view is twice as wide in x as it is in y. If the viewport is twice as wide as it is tall, it displays the image without distortion.

The matrix generated by Glu.Perspective is multipled by the current matrix, just as if Gl.MultMatrix were called with the generated matrix. To load the perspective matrix onto the current matrix stack instead, precede the call to Glu.Perspective with a call to Gl.LoadIdentity.

Given f defined as follows:

$\mathit{f}\mathit{cotangent}\left(\frac{\mathit{fovy}}{2}\right)$

The generated matrix is

$\left(\begin{array}{cccc}\frac{\mathit{f}}{\mathit{aspect}}& 0& 0& 0\\ 0& \mathit{f}& 0& 0\\ 0& 0& \frac{\mathit{zFar}+\mathit{zNear}}{\mathit{zNear}-\mathit{zFar}}& \frac{2×\mathit{zFar}×\mathit{zNear}}{\mathit{zNear}-\mathit{zFar}}\\ 0& 0& -1& 0\end{array}\right)$

### Notes

Depth buffer precision is affected by the values specified for zNear and zFar. The greater the ratio of zFar to zNear is, the less effective the depth buffer will be at distinguishing between surfaces that are near each other. If

$\mathit{r}\frac{\mathit{zFar}}{\mathit{zNear}}$

roughly ${\mathit{log}}_{2}\left(\mathit{r}\right)$ bits of depth buffer precision are lost. Because $\mathit{r}$ approaches infinity as zNear approaches 0, zNear must never be set to 0.

### See also

Gl.MultMatrix

See original documentation on OpenGL website