Linedef type 145, Intangible from Top, Translucent, No Sides, is a type of translucent floor over floor platform which can be fallen through from above, but not jumped through from below. Unlike linedef type 144, this FOF does not render side textures. It is useful for making vertical one-way routes where the sides would not be in view anyway. Since the side textures are not rendered, it requires less CPU power to render.
The flats, floor height, and ceiling height of the FOF are determined by the flats, floor height, and ceiling height of the control sector.
The alpha value of this FOF's translucency can be changed by setting the control linedef's front side upper texture to the number symbol (#), followed by a three-digit decimal number, from 000 to 255. #000 is completely invisible, whereas #255 is completely opaque. Note that in the Software renderer, there are actually only eleven different values: #000–#011, #012–#037, #038–#063, #064–#088, #089–#114, #115–#139, #140–#165, #166–#191, #192–#216, #217–#242, #243–#255, where #000–#011 is invisible, and #243–#255 is opaque. The advantage of using the completely opaque values is the ability to properly render flats which contain transparent pixels. If no value is set in the front side upper texture, however, the default alpha value of #128 will be used.
The light level of the control sector will determine the brightness of the shadow cast by the FOF. If the light level of the control sector is lower than that of the target sector, then it will cast a dark shadow. If the light level of the control sector is higher than that of the target sector, then the FOF will illuminate the area below it. If the light level of the control sector is equal to that of the target sector, then the FOF will not affect the light of the area below it.
If Flag  / No Midtexture Skew / Effect 2 is checked, the inside will be rendered as well. If Flag  / Not Climbable is checked, the FOF will not cast a shadow.
Linedef special info
Height of bottom of FOF
Height of top of FOF
Sector light level
Brightness of shadow cast
Front upper texture
Alpha value of FOF's translucency, from #000 to #255 (#000 is completely invisible, #255 is completely opaque, #128 is default)
 No Midtexture Skew / Effect 2: Inside of FOF is rendered  Not Climbable: No shadow cast