As an aside, I posted this 5 days ago on 2008-06-21, but for some reason I got a message stating that posts on this forum need moderator approval, which I never got. Not sure if that's a forum bug, or a moderator problem. Anyway, here's another try.

My models don't display correctly in my XNA program, even though they look the way I expect them to when I create them in XSI Mod Tool. I would think it could be a problem with my rendering code, except the problem also exists while viewing my models with the FBX plugin for QuickTime. Polygons seem to be in places where they shouldn't be, and when panning, zooming, or orbiting, these extra polygons flicker. I've duplicated the problem with several models, but the steps below seem to be one of the easier ways to reproduce it.

The following set of steps are a quick way to reproduce the problem:

1. View->Layouts->Default
2. Change to wireframe mode, if needed
3. Get->Primitive->Polygon Mesh->Cube. This is cube A.
4. In the properties window that appears, change cube A's length to 16
5. Get->Primitive->Polygon Mesh->Cube. This is cube B.
6. Use the translate tool on the right side of the screen to move cube B to 6,6,0
7. Select cube A, then hold ctrl and select cube B
8. Modify->Poly Mesh->Boolean->Difference
9. Press the "Freeze" button on the bottom right
10. Select cube B, then press the delete key on the keyboard
11. File->Save the model as whatever you wish
12. File->Crosswalk->Export FBX. These are the settings I used. If it's not listed, it was set to disabled.
    • Scene scaling factor = 1.0
    • Geometry = enabled
    • Shapes = enabled
    • Keep XSI effectors = enabled
    • Show the warnings and errors dialog box = enabled
13. Load the exported .fbx in Quicktime with the FBX plugin and you should see the problem

The XSI screenshots look the way I expect them to. The wireframe in QuickTime also looks how I expect. However, the shaded views for both QuickTime and XNA have polygons "covering" the hole that should be cut out of the large cube (cube A).

Changing the cull mode didn't fix anything. I've checked the normals and they look ok. What is causing this, and what can I do to fix it?

Shaded view in XSI (correct)


Wireframe view in XSI (correct)


Shaded view #1 in QuickTime (incorrect - extra polygons that flicker when panning, zooming, orbiting)


Shaded view #2 in QuickTime (incorrect - extra polygons that flicker when panning, zooming, orbiting)


Wireframe view in QuickTime (correct)


Shaded view in XNA (incorrect - extra polygons that flicker when panning, zooming, orbiting)

patsybaby:

As an aside, I posted this 5 days ago on 2008-06-21, but for some reason I got a message stating that posts on this forum need moderator approval, which I never got. Not sure if that's a forum bug, or a moderator problem. Anyway, here's another try.

The forum spam filter catches the occasional post and it goes in the moderation queue where absolutly nobody gets notified other than the poster. Every few months one of the MS guys will see it and it will get magically approved ;-)

Hi, I'm new to XNA and am using Softimage XSI Mod Tools also and I'm experiencing the same problem.

Have you already found a solution for the problem?

Nope. I have no clue as to how to fix it.

I don't know about quicktime, but I think I can help for XNA. I'm going to go ahead and assume that your object is kind of small (under 10 world units in overall size). Go to where the near and far values are set for the camera's projection in your XNA app and make them something like 1 to 100 and see if that helps. In the past I've noticed models flickering just as you have described, it seemed to me that there was a magic ratio between the average distance between vertices of the model and the distance of the camera's far plane. I don't know what the ratio is, but I was able to get rid of the flicker by playing with the far plane distance.

Thanks for the suggestion, but it didn't make any difference. The thing is, the polygons that are flickering shouldn't even be there. In the QuickTime shaded views #1 and #2, and the screenshot of my XNA app, there are polygons covering the "hole" that should be in the cube (see the XSI shaded view screenshot for correct results). These are the polygons that flicker when the camera moves. The rest of the cube seems fine.

Someone suggested to me that maybe it was a problem with using a boolean difference, since some modeling programs apparently do funny stuff with that. However, I've had the same result on models that don't use any booleans. This cube was just an example I quickly whipped up that had an easy to reproduce set of instructions. I actually never used a boolean until I started this example.

You may want to look through this tutorial. Apparently there's a couple of fancy things you need to do to get XSI Mod Tool and XNA working together.