自己解决！
把vpLightLobe的setIsectEnable设置为false，帧率就回来了。
看看setIsectEnable的解释：
/**
* Set the state of isectors for this light lobe. Setting the isectors
* for a light lobe to inactive can save compute resources at the expense
* of not recalculating the intersection of the light cone with the scene.
* If a light is not moving around in an area where the surface that the
* beam intersects will change height or orientation, it may be prudent to
* disable isectors and let it assume that the position and orientation of
* the intersecting surface is static. Note that it is OK to move the
* light source itself, and change its orientation, and the light will
* still be projected correctly as long as the projection surface maintains
* the same height and orientation.
*/ |
