edge artifact with alpha channel

General TouchDesigner Discussion
1

Hello,

I’m getting in trouble trying to do some basic 3D compositing.

Here a simple scene: a mesh (terrain) and a rectangle with an image( with an alpha channel).
As you can see on the screenshot, if my render is set with any anti alias over 1, I have some artifact at the edge of the image. With an Anti alias set to 1 the problem disappear.
I have played with all option (shader + render setting) with no luck.

I don’t remember having any issue like that before.
I’m running TD088 64 /11760 (nvidia driver 320.49)

antialasing x1.png

antialasing x4.png

Any Idea ???

Edit
"I have just found the answer : in the phong /common / discard pixels based on Alpha set to on "

Thanks

xavier

2

Any chance you could share the .toe file with me at support@derivative.ca?

3

No problem Malcom.
I will post it later.

Xavier.

4

This is an issue that can occur when mixing Order Independent transparency with anti-aliasing. You may be able to avoid this feature in this case by ensuring your BG is drawn first (using the Draw Priority in the ‘Render/Display’ tab of the Geometry COMP. Sorting your particles by distance to the camera (click the ‘reverse’ option too since you want it farthest to closest, not closest to farthest) using the Sort SOP will help artifacts that occur between the particles.

5

Hello Malcom,

In my case the Draw priority doesn’t play any role at all.

Discard pixel based on alpha must be on.

and, I believe it is a kind of bug. The texture must have transparent pixel around the edge.
Otherwise you get that kind of edge artifact :

ScreenClip.png
ScreenClip.png931×546 181 KB

Here you have a comp with both 2 textures generated with a rectangle top.

An easy workaround, if you want to play with “image card” is to add a small margin (alpha=0) around the edge.

demo_edge problem.toe (9.01 KB)

Xavier.