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I have a short animation involving two text objects and blender internal. They have a shadeless black material and simply pop on screen in front of another shadeless material, this one white. The objects are not close enough together for any intersections.

The final render shows the text flickering in and out of existence. I also noticed that other curve objects like the rope of my price-tag, display a strange fragmentation where they come close to intersecting (but don't). I am really mystified by this one.

If someone could try to reproduce my issue the blend file is attached and I'd appreciate any comments trying to narrow down the issue. Thanks!

-Jesse

flicker issue

Blend:

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  • $\begingroup$ Have you try this project with old blender 2.73a I tracked introduction of flickering errors to blender 2.74 and not fixed. The last version 2.74 to 2.78a is having flickering error in animation. youtu.be/lIv6qLm5WfU $\endgroup$
    – user31996
    Commented Oct 28, 2016 at 8:43

3 Answers 3

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The problem seems to be because of your camera's clipping options. Where clipping settings are

You have these starting from 1mm and continuing to 10km, while limits closer to the actual visible range of your scene would be more sensible.

I'm cutting some corners about the actual math involved, but basically the way these settings work, is that the range you have set is divided into different distance steps to the camera, within possible computing precision, when determining what things are in front or behind other things. There is limited precision in this rendering code for this distance information, so bigger range for the camera clipping means bigger steps in comparing distances, so objects with only a small distance between them might end up in the same distance step and go in the wrong order.

Having smaller clipping range makes also these steps smaller, so the rendering code is able to differentiate between smaller distances as well. Note that there's a lot more of this precision near the "near" plane than near the "far" plane, so increasing the "Start" value might have even more impact than reducing the "End" value, even if the amount you change it is far less.

A range from 1m to 300m or so would be ok for your scene.

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  • $\begingroup$ Thanks for the thorough explanation! That's great and solved my issue. I had the clipping set so large from a previous file and didn't realize it could affect the distance step as you described. Lesson learned! Cheers. $\endgroup$
    – HowToBlend
    Commented May 31, 2016 at 23:31
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The start clipping distance of the camera is too small. Increase it to 1m in the Lens panel of the Camera object data header and everything'll be running fine. enter image description here enter image description here

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  • $\begingroup$ Thanks a lot for your answer and for taking the time to make the gif. As with the other guys, I didn't realize that clipping values could have this effect. Thanks again. $\endgroup$
    – HowToBlend
    Commented May 31, 2016 at 23:33
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The scale of the scene is quite large, >100 metres along the X-axis. With 200 metres, the distance to the camera is also quite large. The near clipping distance, however, is set to 1mm, and the far clipping distance is set at 10km. With such a huge difference between the clipping distances, you're going to see the result of floating point imprecision of the computer. It's gone when you set the clipping to 100m and 300m, which still comfortably encloses your scene. That way you get the precision where it matters.

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    $\begingroup$ Thanks for your answer! I had no idea that clipping was sensitive in this way. Good to know. $\endgroup$
    – HowToBlend
    Commented May 31, 2016 at 23:32

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