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Alfa Blend Problem

Martin Weare

100RPM
Mar 17, 2009
117
0
Ive been working on some road paint textures and Im getting hairline white lines along the edges where it should be invisible. The dds files are dx3 explicit alpha. Any tricks to stop this problem ?

The reason im using alpha and a wider canvas is because I'm trying to keep the different lines consistent. So of I change to double lines or wider lines in the same wall they line up properly.


 

R Soul

1000RPM
Apr 19, 2009
1,009
212
37
It's something to do with they way the colours of pixels in the texture are smoothly blended into the surrounding pixels. The pixels around the edge of the image are smoothly blended to the pixels on the other side. That's to allow for seamless tiling.

A possible solution is to offset your texture in your image program so that all the pixels at one edge are a similar colour to the ones on the opposite edge. Say you have a track texture with a white line going right up to the edge of the left side, and you set that to join your main track, on the left hand side. Where it meets the track is the right side of the image, which will be gradually blending to the white because that's what's on the other side of the image. You could try offsetting your image so that the white line runs down the middle, then use Venue Materials to undo the offset.
 

Brendon Pywell

Bob's Track Builder
Feb 26, 2009
418
156
Changes the X Scale to 0.99. You might need to change the X Offset to 0.01.

Alternatively change the texture so that the white line is not on the edge of the image; sop that you have clear space either side of it.
 

woochoo

250RPM
Mar 16, 2009
332
49
edit: doh, missed it by that much...
i think he means move it a couple of pixels away from the edge, parallel.
it seems like a similar thing to when one sees a black line at the top of their trees when the alpha mask isn't quite right.

i think it's mip maps that cause the blending of the edges, but in doing so they also do a 'fake antialiasing' if you like, when the textures are a small way off in the distance by switching to lower res versions, the same function as setting lower texture detail i believe. you can set the mip bias in the textures panel to -2,-3 etc to adjust the distance at which it will do the blend/bluring as well. but moving the line slightly away from the edge of the texture should do the trick.
 

Brendon Pywell

Bob's Track Builder
Feb 26, 2009
418
156
yea, i tried that clear space thing, it improved it but not perfect. Thanks for explaining offset
Add more space and I think it will fix it. How much space depends really on how big the final poly is.

As a guide, use half the width for your white line. So if the white line is 16 pixels wide, add 8 pixels either side as blank.

If you're still having trouble, upload the image. :wink2:
 

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