transparent（直接定义材料是否透明）
官网解释：
Defines whether this material is transparent（透明）. This has an effect on rendering as transparent objects need special treatment and are rendered after non-transparent objects.
When set to true, the extent to which the material is transparent is controlled by setting it’s opacity property.
Default is false.
opacity（可以调节透明的程度，0.0表示完全透明，1.0表示完全不透明）
官网的解释：
Float in the range of 0.0 - 1.0 indicating how transparent the material is. A value of 0.0 indicates fully transparent, 1.0 is fully opaque（不透明）.
If the material’s transparent property is not set to true, the material will remain fully opaque and this value will only affect its color.
Default is 1.0.
emissiveIntensity
官网解释：
Intensity of the emissive（放射） light. Modulates the emissive color. Default is 1.
.envMapIntensity : Float
官网解释：
Scales the effect of the environment map by multiplying its color.
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