• Products
  • Solutions
  • Made with Unity
  • Learning
  • Support & Services
  • Community
  • Asset Store
  • Get Unity

UNITY ACCOUNT

You need a Unity Account to shop in the Online and Asset Stores, participate in the Unity Community and manage your license portfolio. Login Create account
  • Blog
  • Forums
  • Answers
  • Evangelists
  • User Groups
  • Beta Program
  • Advisory Panel

Navigation

  • Home
  • Products
  • Solutions
  • Made with Unity
  • Learning
  • Support & Services
  • Community
    • Blog
    • Forums
    • Answers
    • Evangelists
    • User Groups
    • Beta Program
    • Advisory Panel

Unity account

You need a Unity Account to shop in the Online and Asset Stores, participate in the Unity Community and manage your license portfolio. Login Create account

Language

  • Chinese
  • Spanish
  • Japanese
  • Korean
  • Portuguese
  • Ask a question
  • Spaces
    • Default
    • Help Room
    • META
    • Moderators
    • Topics
    • Questions
    • Users
    • Badges
  • Home /
avatar image
3
Question by HppyDedPxl · Dec 26, 2016 at 09:27 PM · shaderverticesprojectiongrabrefraction

What do these lines in the refraction shader actually do? (UV calculation)

Hello. I've been studying the refraction shader and I am not exactly sure what the following lines do :

 o.uvgrab.xy = (float2(o.vertex.x, o.vertex.y) + o.vertex.w) * 0.5;
 o.uvgrab.zw = o.vertex.zw;
 

this value is later used in

     half4 col = tex2Dproj(_GrabTexture, UNITY_PROJ_COORD(i.uvgrab));

I am assuming that those lines calculate the position of the vertex on the Grab Texture, transforming it back into projection (or view? not sure) space. So getting the x and y position, then using the w property, which stores projection displacement, to get the vertex back to the near clipping plane, then multiplying by 0.5 to convert it from a coordinate system with it's origin in the center to the screen space coordinate system?

It would be amazing if somebody could clear this up for me, since everyone seems to just use this and never comment on what exactly it does. (probably because it's really basic...)

Thanks in advance!

Comment
Add comment · Show 2
10 |3000 characters needed characters left characters exceeded
▼
  • Viewable by all users
  • Viewable by moderators
  • Viewable by moderators and the original poster
  • Advanced visibility
Viewable by all users
avatar image Socapex · Dec 28, 2016 at 08:50 PM 0
Share

Ok so you've picked my interest. Please chime in if you figure it out, this is killing me lol.

To get the projected space, you would divide by w. Simply adding the w component is very strange, it does not seem to have any mathematical sense what-so-ever. I'm guessing this is a "trick" to achieve a visual effect at low cost.

Thats all for now, I can't wrap my head around that manipulation -___-

Show more comments

0 Replies

· Add your reply
  • Sort: 

Your answer

Hint: You can notify a user about this post by typing @username

Up to 2 attachments (including images) can be used with a maximum of 524.3 kB each and 1.0 MB total.

Welcome to Unity Answers

If you’re new to Unity Answers, please check our User Guide to help you navigate through our website and refer to our FAQ for more information.

Before posting, make sure to check out our Knowledge Base for commonly asked Unity questions.

Check our Moderator Guidelines if you’re a new moderator and want to work together in an effort to improve Unity Answers and support our users.

Follow this Question

Answers Answers and Comments

7 People are following this question.

avatar image avatar image avatar image avatar image avatar image avatar image avatar image

Related Questions

Project a shape using a mesh 0 Answers

Cube botttom transparent with shader? 1 Answer

Water4 with Refraction 0 Answers

How to apply refraction at marked texture pixels while the rest is being rendered normal? 1 Answer

Get the screen coordinates of an object altered by Fisheye 0 Answers


Enterprise
Social Q&A

Social
Subscribe on YouTube social-youtube Follow on LinkedIn social-linkedin Follow on Twitter social-twitter Follow on Facebook social-facebook Follow on Instagram social-instagram

Footer

  • Purchase
    • Products
    • Subscription
    • Asset Store
    • Unity Gear
    • Resellers
  • Education
    • Students
    • Educators
    • Certification
    • Learn
    • Center of Excellence
  • Download
    • Unity
    • Beta Program
  • Unity Labs
    • Labs
    • Publications
  • Resources
    • Learn platform
    • Community
    • Documentation
    • Unity QA
    • FAQ
    • Services Status
    • Connect
  • About Unity
    • About Us
    • Blog
    • Events
    • Careers
    • Contact
    • Press
    • Partners
    • Affiliates
    • Security
Copyright © 2020 Unity Technologies
  • Legal
  • Privacy Policy
  • Cookies
  • Do Not Sell My Personal Information
  • Cookies Settings
"Unity", Unity logos, and other Unity trademarks are trademarks or registered trademarks of Unity Technologies or its affiliates in the U.S. and elsewhere (more info here). Other names or brands are trademarks of their respective owners.
  • Anonymous
  • Sign in
  • Create
  • Ask a question
  • Spaces
  • Default
  • Help Room
  • META
  • Moderators
  • Explore
  • Topics
  • Questions
  • Users
  • Badges