Author Topic: Unusual Situation with FBP Fences in FS9  (Read 3137 times)


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Unusual Situation with FBP Fences in FS9
« on: February 26, 2017, 04:38:30 PM »
I thought some of you might like to know about a problem I recently experienced with FS9 - and the fix for it.

Updating my FS9 version CYYJ, I added a fence in the Pat Bay area. (See SS1). Up close, the fence appears normal. Back off a little and things change. (See SS2). Instead of the asphalt being seen through the fence, you see the underlying landclass. The asphalt is the top of a 3D model. There is also a platform under the asphalt. The distance at which the changeover occurs varies with the viewing azimuth. The fence is generated by FenceBuilder PRO and there is only one LOD.

The effect only occurs (at least apparently) in this situation. Fences over aprons and ground polys do not show this characteristic. I have prefaced the asphalt texture name with ZBIAS to ensure it is drawn last, but the landclass shows through anyway.

While it can't be seen in these screenshots, if the viewing angle is low such that a portion of a building is behind the fence, the building displays instead on the landclass.


It turns out not all DXT-3 textures are equal. (FBP textures generally, by necessity, are DXT3.)  It is well-known that DXT-3 textures can be problematic.  And so it was in this case.

It occurred to me that in the absence of a second LOD, there had to be another reason for this discontinuity. Mipmaps!. So, I eliminated the mipmaps and tried again. To my surprise, a similar thing happened at the same time but the display of the show-through landclass was "grainer", presumably due to the non-mipmapped alpha. It seems that DXT-3 file still "assumed" there were mipmaps in the file.

I then converted the texture to DXT-1 (using ImageTool) and the problem disappeared. But then, I inadvertently saved the texture back into the original folder as DXT-3. STILL OK!

So, with a hex editor, I compared that DXT-3 file with the original. There were major differences! The RGBQUADs in the latter case were all 0's. Not so with the original file. There were also similar differences in the bitmap data. I don't recall what tool I used to generate the original texture, but it was probably DXTbmp.

I would note that simply loading the original DXT-3 file into ImageTool and saving it immediately had no effect - presumably because ImageTool "knew" no changes had been made. But, with an intermediate conversion and save as DXT-1 and then converting back to DXT-3, the "new-format" DXt-3 file was saved and the problem was eliminated.



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Re: Unusual Situation with FBP Fences in FS9
« Reply #1 on: February 27, 2017, 06:13:32 PM »
Thanks Don !!