glPolygonOffset解决两个面共面

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