# Can someone explain why there are trails for the ellipse?

**URL:** <https://discourse.processing.org/t/can-someone-explain-why-there-are-trails-for-the-ellipse/22455>\
**Category:** Beginners\
**Created:** [July 7, 2020, 6:19pm UTC](https://discourse.processing.org/t/can-someone-explain-why-there-are-trails-for-the-ellipse/22455 "2020-07-07T18:19:22Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![BSiemens](https://yyz2.discourse-cdn.com/flex036/user_avatar/discourse.processing.org/bsiemens/32/216_2.png) [@BSiemens](https://discourse.processing.org/u/BSiemens)\
**Post date:** [July 7, 2020, 6:19pm UTC](https://discourse.processing.org/t/can-someone-explain-why-there-are-trails-for-the-ellipse/22455/1 "2020-07-07T18:19:22Z")

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[https://p5js.org/examples/structure-create-graphics.html](https://p5js.org/examples/structure-create-graphics.html)

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**Author:** ![glv](https://yyz2.discourse-cdn.com/flex036/user_avatar/discourse.processing.org/glv/32/18785_2.png) [@glv](https://discourse.processing.org/u/glv)\
**Post date:** [July 7, 2020, 6:22pm UTC](https://discourse.processing.org/t/can-someone-explain-why-there-are-trails-for-the-ellipse/22455/2 "2020-07-07T18:22:21Z")

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Hello,

I am someone!  
[https://p5js.org/learn/color.html](https://p5js.org/learn/color.html)  
[https://p5js.org/reference/#/p5/fill](https://p5js.org/reference/#/p5/fill)

```auto
fill(gray, [alpha])

```

`:)`

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<div class="post-metadata">

**Author:** ![BSiemens](https://yyz2.discourse-cdn.com/flex036/user_avatar/discourse.processing.org/bsiemens/32/216_2.png) [@BSiemens](https://discourse.processing.org/u/BSiemens)\
**Post date:** [July 7, 2020, 6:34pm UTC](https://discourse.processing.org/t/can-someone-explain-why-there-are-trails-for-the-ellipse/22455/3 "2020-07-07T18:34:33Z")

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Why does the alpha channel of something drawn behind the ellipse create the trail?

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**Author:** ![slow\_izzm](https://yyz2.discourse-cdn.com/flex036/user_avatar/discourse.processing.org/slow_izzm/32/5637_2.png) [@slow\_izzm](https://discourse.processing.org/u/slow_izzm)\
**Post date:** [July 7, 2020, 6:52pm UTC](https://discourse.processing.org/t/can-someone-explain-why-there-are-trails-for-the-ellipse/22455/4 "2020-07-07T18:52:45Z")

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Because each time `fill()` is invoked it is only applying 0.047% opacity over what was previously drawn. `draw()` runs aprox 60 times per second …

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<div class="post-metadata">

**Author:** ![BSiemens](https://yyz2.discourse-cdn.com/flex036/user_avatar/discourse.processing.org/bsiemens/32/216_2.png) [@BSiemens](https://discourse.processing.org/u/BSiemens)\
**Post date:** [July 7, 2020, 6:54pm UTC](https://discourse.processing.org/t/can-someone-explain-why-there-are-trails-for-the-ellipse/22455/5 "2020-07-07T18:54:28Z")

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Of course. Thanks! Now I have to include more characters or it won’t let me post.

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**Author:** ![slow\_izzm](https://yyz2.discourse-cdn.com/flex036/user_avatar/discourse.processing.org/slow_izzm/32/5637_2.png) [@slow\_izzm](https://discourse.processing.org/u/slow_izzm)\
**Post date:** [July 7, 2020, 6:58pm UTC](https://discourse.processing.org/t/can-someone-explain-why-there-are-trails-for-the-ellipse/22455/6 "2020-07-07T18:58:25Z")

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just in case you are unfamiliar, this is a great resource for beginners …

https://www.youtube.com/embed/videoseries?list=PLRqwX-V7Uu6Zy51Q-x9tMWIv9cueOFTFA&wmode=transparent&rel=0&autohide=1&showinfo=1&enablejsapi=1