glNormal3fv/GL_RESCALE_NORMAL/GL_NORMALIZE

法线向量的设置也是状态，设置顶点时候会用最近的法线向量。

glBegin(xxx);
glNormal3fv(vn0);
glVertex3fv(v0);

glNormal3fv(vn1);
glVertex3fv(v1);
glEnd();

计算光照前需要对法向量进行单位化。

1）.如果一开始就是单位向量，后面只是进行平移和旋转，那么法向量不需要重新计算，也不需要重新规范化。

2）.glEnable(GL_RESCALE_NORMAL) 对于开始有规范化的法向量，其中进行了均匀缩放的，那么需用GL_RESCALE_NORMAL重新规范化法向量，会比GL_NORMALIZE更快。如果是单位化了的法线向量（例如3ds
max中导出的法线贴图），那么模型均匀缩放后，可以用GL_RESCALE_NORMAL重新规范化法向量。

3）.glEnable(GL_NORMALIZE) 对于开始没有规范化的法向量，或者网格进行了非均匀缩放，那么需要重新程序员手动计算法向量的值（不要轻易非均匀缩放），且要进行GL_NORMALIZE规范化法向量。

Name

glNormal — set the current normal vector

C Specification

void glNormal3b(	GLbyte nx,
	GLbyte ny,
	GLbyte nz ) ;

 

void glNormal3d(	GLdouble nx,
	GLdouble ny,
	GLdouble nz ) ;

 

void glNormal3f(	GLfloat nx,
	GLfloat ny,
	GLfloat nz ) ;

 

void glNormal3i(	GLint nx,
	GLint ny,
	GLint nz ) ;

 

void glNormal3s(	GLshort nx,
	GLshort ny,
	GLshort nz ) ;

 

Parameters

nx

, 

ny

, 

nz

Specify the x, y, and z coordinates of the new current normal. The initial value of the current normal is the unit vector, (0, 0, 1).

C Specification

void glNormal3bv(

const GLbyte * v ) ;

 

void glNormal3dv(

const GLdouble * v ) ;

 

void glNormal3fv(

const GLfloat * v ) ;

 

void glNormal3iv(

const GLint * v ) ;

 

void glNormal3sv(

const GLshort * v ) ;

 

Parameters

v

Specifies a pointer to an array of three elements: the x, y, and z coordinates of the new current normal.

Description

The current normal is set to the given coordinates whenever 

glNormal

 is issued. Byte, short, or integer arguments are converted to floating-point format with a linear mapping that maps the most positive representable integer
value to 1.0 and the most negative representable integer value to -1.0 .

Normals specified with 

glNormal

 need not have unit length. If 

GL_NORMALIZE

 is enabled, then normals of any length specified with 

glNormal

 are normalized after transformation.
If 

GL_RESCALE_NORMAL

 is enabled, normals are scaled by a scaling factor derived from the modelview matrix. 

GL_RESCALE_NORMAL

 requires that the originally specified normals were of unit length, and
that the modelview matrix contain only uniform scales for proper results. To enable and disable normalization, callglEnable and glDisable with
either 

GL_NORMALIZE

 or 

GL_RESCALE_NORMAL

. Normalization is initially disabled.

Notes

The current normal can be updated at any time. In particular, 

glNormal

 can be called between a call to glBegin and
the corresponding call to glEnd.

Associated Gets

glGet with argument 

GL_CURRENT_NORMAL

glIsEnabled with argument 

GL_NORMALIZE

glIsEnabled with argument 

GL_RESCALE_NORMAL

See Also

glBegin, glColor, glIndex, glMultiTexCoord, glNormalPointer, glTexCoord, glVertex

Copyright

Copyright © 1991-2006 Silicon Graphics, Inc. This document is licensed under the SGI Free Software B License. For details, see http://oss.sgi.com/projects/FreeB/.