OpenGL学习记录（一）

有关depth test / culling

Depth testing is an effective technique for hidden surface removal, and OpenGL has functions that do this for you behind the scenes. The concept is simple: When a pixel is drawn, it is assigned a value (called the z value) that denotes its distance from the viewer's perspective. Later, when another pixel needs to be drawn to that screen location, the new pixel's z value is compared to that of the pixel that is already stored there. If the new pixel's z value is higher, it is closer to the viewer and thus in front of the previous pixel, so the previous pixel is obscured by the new pixel. If the new pixel's z value is lower, it must be behind the existing pixel and thus is not obscured. This maneuver is accomplished internally by a depth buffer with storage for a depth value for every pixel on the screen

Culling is the term used to describe the technique of eliminating geometry that we know will never be seen. By not sending this geometry to your OpenGL driver and hardware, you can make significant performance improvements. One culling technique is backface culling, which eliminates the backsides of a surface.

以下是对相关数据的测试
前提:

设置为外表面顺时针,顺时针为front,（即外表面为Front）椎体未作任何旋转是顶尖向外

glFrontFace(GL_CW);

if(bCull)

glEnable(GL_CULL_FACE);

else

glDisable(GL_CULL_FACE);

//启动深度测试

if(bDepth)

glEnable(GL_DEPTH_TEST);

else

glDisable(GL_DEPTH_TEST);