Replacement for gluPerspective
For those interested, I have coded a replacment for gluPerspective so people can do away with dependancies on glu as well as glut!
1 2 3 4 5 6 7 8 | // Replaces gluPerspective. Sets the frustum to perspective mode.// fovY - Field of vision in degrees in the y direction// aspect - Aspect ratio of the viewport// zNear - The near clipping distance// zFar - The far clipping distancevoid perspectiveGL( GLdouble fovY, GLdouble aspect, GLdouble zNear, GLdouble zFar ){ |
Very long (& in theory accurate!) version of Pi. Hopefully an optimizing compiler will replace references to this with the value!
1 | const GLdouble pi = 3.1415926535897932384626433832795; |
Half of the size of the x and y clipping planes.
1 | GLdouble fW, fH; |
Calculate the distance from 0 of the y clipping plane. Basically trig to calculate position of clipper at zNear.
Note: tan( double ) uses radians but OpenGL works in degrees so we convert degrees to radians by dividing by 360 then multiplying by pi.
Formula below corrected by Carsten Jurenz:
1 | fH = tan( (fovY / 2) / 180 * pi ) * zNear; |
Which can be reduced to:
1 | fH = tan( fovY / 360 * pi ) * zNear; |
Calculate the distance from 0 of the x clipping plane based on the aspect ratio.
1 | fW = fH * aspect; |
Finally call glFrustum, this is all gluPerspective does anyway! This is why we calculate half the distance between the clipping planes - glFrustum takes an offset from zero for each clipping planes distance. (Saves 2 divides)
1 2 | glFrustum( -fW, fW, -fH, fH, zNear, zFar );} |
Download The Code Here: Perspective GL.
Email: James Heggie.