# Question about setScissorRect

**URL:** <https://forums.kodeco.com/t/question-about-setscissorrect/82965>\
**Category:** Metal by Tutorials\
**Created:** [September 26, 2019, 1:44am UTC](https://forums.kodeco.com/t/question-about-setscissorrect/82965 "2019-09-26T01:44:40Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![markusm](https://assets.chunter.kodeco.com/user_avatar/forums.kodeco.com/markusm/32/81494_2.png) [@markusm](https://forums.kodeco.com/u/markusm)\
**Post date:** [September 26, 2019, 1:44am UTC](https://forums.kodeco.com/t/question-about-setscissorrect/82965/1 "2019-09-26T01:44:40Z")

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Hi,

I have a question about setScissorRect. When it is applied will it prevent computation of pixels outside of this rectangle or does it just clip the output when everything is computed ?

In other words, can it be used as an optimization tool to limit shader computations ?

Thanks a lot. Great book btw.

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**Author:** ![caroline](https://assets.chunter.kodeco.com/user_avatar/forums.kodeco.com/caroline/32/111867_2.png) [@caroline](https://forums.kodeco.com/u/caroline)\
**Post date:** [September 26, 2019, 3:27am UTC](https://forums.kodeco.com/t/question-about-setscissorrect/82965/2 "2019-09-26T03:27:24Z")

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The documentation says _The rendering pipeline discards fragments that lie outside the scissor rectangle._  
So yes it is an optimization - fragment functions won’t be performed on fragments outside the scissor rectangle.

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<div class="post-metadata">

**Author:** ![markusm](https://assets.chunter.kodeco.com/user_avatar/forums.kodeco.com/markusm/32/81494_2.png) [@markusm](https://forums.kodeco.com/u/markusm)\
**Post date:** [September 26, 2019, 4:44am UTC](https://forums.kodeco.com/t/question-about-setscissorrect/82965/3 "2019-09-26T04:44:56Z")

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Thanks for the answer Caroline. I was just not sure if it was discarded before or after computation 🙂