摘自http://www.gamergroup.cn/html/78/n-3078.html
当两个面共面时,会出现十分难看的z - fighting 问题,
要解决此问题可以使用, Polygon Offset, 方法如下:
drawSomething();
//同一位置绘制另一个东西
glEnable( GL_POLYGON_OFFSET_FILL ); // This is the one we need...
glPolygonOffset( g_OffsetFactor, g_OffsetUnit );
drawOtherthing();
glPolygonOffset( 0.0f, 0.0f );
glDisable( GL_POLYGON_OFFSET_FILL );
其中
g_OffsetFactor代表 factor,
g_OffsetUnit 代表 units,
关于factor, units 的解释如下:
When GL_POLYGON_OFFSET is enabled, each fragment's depth
value will be offset after it is interpolated from the depth
values of the appropriate vertices. The value of the offset
is factor * DZ + r * units, where DZ is a measurement of
the change in depth relative to the screen area of the
polygon, and r is the smallest value that is guaranteed to
produce a resolvable offset for a given implementation. The
offset is added before the depth test is performed and
before the value is written into the depth buffer.
glPolygonOffset is useful for rendering hidden-line images,
for applying decals to surfaces, and for rendering solids
with highlighted edges.


这个函数以后可能用得到,tutorial04里面画阴影的时候用到了,不过阴影还是很难看