学步园

http://www.glprogramming.com/dgs.php?dg=1

An Alternative to gluPerspective by Dranith

Motive 

gluPerspective is a very very handy function for setting up the projection matrix. The only problem it has that I see is the FOV it takes is the FOV in the Y direction. So either you have no control over the FOV in the X direction, or you have the source to gluPerspective and you do some fancy trig to figure out the Y FOV value you need to input to get the desired X FOV. 

Both these ways suck. So heres the code that lets you specify the FOV in the X direction. Code is based off the MESA implementation of gluPerspective. 

Not to mention this is a point of confusion for people new to OpenGL. I didn't even notice that it took the Y FOV till a few days ago when I was doing something that I needed to be able to specify in X and things weren't working =). 

void gldPerspective(GLdouble fovx, GLdouble aspect, GLdouble zNear, GLdouble zFar)<br /> {<br /> // This code is based off the MESA source for gluPerspective<br /> // *NOTE* This assumes GL_PROJECTION is the current matrix</p> <p> GLdouble xmin, xmax, ymin, ymax;<br /> GLdouble m[16] = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};<br /> xmax = zNear * tan(fovx * M_PI / 360.0);<br /> xmin = -xmax;</p> <p> ymin = xmin / aspect;<br /> ymax = xmax / aspect;<br /> // Set up the projection matrix<br /> M(0,0) = (2.0 * zNear) / (xmax - xmin);<br /> M(1,1) = (2.0 * zNear) / (ymax - ymin);<br /> M(2,2) = -(zFar + zNear) / (zFar - zNear);<br /> M(0,2) = (xmax + xmin) / (xmax - xmin);<br /> M(1,2) = (ymax + ymin) / (ymax - ymin);<br /> M(3,2) = -1.0;<br /> M(2,3) = -(2.0 * zFar * zNear) / (zFar - zNear);</p> <p> // Add to current matrix<br /> glMultMatrixd(m);<br /> }

Notes 

Usage syntax is exactly the same as gluPerspective. This function assumes that GL_PROJECTION is the current matrix. This code is not optimised at all, but should only need to be called once. 

--Dranith