OSG Exporter - Texture seams somehow have alpha

[JvdBosch]

Michael,

Thanks for your input and effort. However the problem still exists... I already had GL_SAMPLE_ALPHA_TO_COVERAGE_ARB enabled on the model (there are thousands of trees in the complete model). And tiling is enabled on the wall texture.

I've put together a zip of all files with a test script. You can find it here.

Both the wall texture and the tree texture exhibit the same type of problem at the edges of the texture. When exporting the same model in previous versions of 3DS Max there were no issues...

[Veleno]

Hi JvdBosch,

I took a look at the files in your model.

■ Tree Lines: Tiling is the cause of the lines appearing on the trees, though I see I wasn't very clear in my previous post what part of the model I was talking about.
■ Wall Transparency: Your wall texture, baksteen_CrRedGrain (Custom).bmp, has an alpha channel. The alpha is slightly gray at the borders, and this is causing the transparency issue. I'd guess the gray border probably came from re-scaling the image. I've attached a copy of the BMP with the alpha channel removed (.zip), along with a screenshot showing the problem. In Vizard, any alpha channel found in the diffuse texture is automatically used for transparency. (Bitmap_Alpha_Issue.jpg)
■ Multisampled Alpha: The code looks correct and the effect works correctly for me in the provided example. If this isn't working on yours, then my best guess at the moment is that it may not be supported by your graphics card. I've attached a screenshot of what it looks like on my workstation with an unmodifed version of your tree model (Tree_SampledAlpha_NoLineFix.jpg). When multisampled alpha is working correctly, you should see a screen door artifact when close to the transparent parts of a model (ScreenDoorArtifact.jpg). This artifact lessens at higher multisampling levels, though the banding generally stays.

[JvdBosch]

Michael,

WALL
Thanks for looking at the model. I see now there is indeed a alpha channel in the texture, my bad! This was no issue in previous versions of the exporter/MAX/Vizard using the same textures/models. That's why I didn't suspect the problem to be with the texture.

When I set the exporter to not export opacity maps and use DXT1 it still exports the alpha channel within the diffuse texture image? I guess this behavior has changed since MAX2013 or the new exporter or the latest Vizard? That could explain it, since I used this setting in earlier versions without this problem.

TREE
Regarding the tree, I'm using a GTX680 with the latest drivers. The multisample alpha was and is working fine. The lines are the biggest problem. You say tiling is the answer, so I enabled it. But then you see lines on the top of the tree from the repeating of the treetrunk. See the picture below.

Why is tiling an issue? It never was with previous versions... I find it peculiar to have to set tiling to 0.98 or so to solve a problem which did not exist previously. My complete model has several hundreds of objects with a non-tiled texture. There must be a better way to solve this problem.

Thanks,

Jaap

[Veleno]

Hi Jaap,

Wall:
■ Setting the exporter to DXT1 does appear to be converting alpha channels to 1 bit alpha instead of discarding them, which is odd. The compression ratio still appears to be correct for DXT1. I'm unsure whether this is functioning as intended.

■ Unchecking opacity under maps prevents max from exporting any maps placed in the Opacity slot of a material, which can also be used for transparency.

■ In general, I'd recommend avoiding alpha channels in maps that don't need them. When looking at a model in Inspector, the texture panel will show the format as RGBA if an alpha channel exists for the texture. If not, it will show RGB instead.

Tree:
There are a few ways to fix the issue:

■ Max Method: I've attached a maxscript that will loop through all scene materials (Standard and Standard contained in a multi-material), check for diffuse and opacity maps where tiling is disabled, and if so apply the above tweak. To use it, go to Maxscript -> Run Script... and select Jaap_TweakTiling_2012-01-03.ms.

■ OSGT Method: Save transparent file as OSGT. Open up the plain text model file in your favorite text editor, then use Find and Replace to replace all instances of CLAMP_TO_BORDER with CLAMP_TO_EDGE (case sensitive).

■ Vizard Method: Loop through all textures on the transparent model, changing all tiling that is currently viz.CLAMP_TO_BORDER to viz.CLAMP_TO_EDGE. See the Texture Wrapping entry in the help docs.

The way the exporter currently functions is consistent with how max handles them, at least as far as the diffuse texture goes. However, it does seem like it would be more beneficial, especially in cases like this, to include an option to repeat the texture's edge pixels instead.