Hi !
Featured games (91)
games approved by the League of Dukes
Games in Showcase (757)
Games in Android Showcase (229)
games submitted by our members
Games in WIP (844)
games currently in development
News: Read the Java Gaming Resources, or peek at the official Java tutorials
    Home     Help   Search   Login   Register   
Pages: [1]
  ignore  |  Print  
  JOGL Shader Questions  (Read 2187 times)
0 Members and 1 Guest are viewing this topic.
Offline ghostsoldier23

Junior Devvie

Medals: 1

« Posted 2013-03-24 18:00:03 »

I'm trying to figure out how to start using GLSL with JOGL to do pixel shading on images drawn to GLAutoDrawable via glDrawPixels.

I'm confused as to how a few things work in GLSL:
1) How can I access the color of the current pixel in the shader call?  What is the form of that pixel (RGB, BGR, etc.) so that I can unpack it?
2) Do I just assign gl_FragColor to change the pixel?
3) How do I get coordinates of the current pixel?
4) Does it generally make more sense to perform lighting calculations in the GLSL frag shader or maybe in OpenCL?

I've trying really hard to muddle through learning JOGL by myself, but I'm really stuck on these fundamental problems with GLSL, and I haven't been able to find consistent help through Google.

Any help is appreciated, and I thank you in advance for your time.
Offline davedes
« Reply #1 - Posted 2013-03-24 18:48:33 »

1) The "current pixel" is not known. If you want post-processing, then typically you would render the screen to an FBO texture, and then in your post shader sample from the texture in order to "get the screen pixel."

2) Yep; unless you are using GLSL 130+ in which case you would use a custom out attribute.

3) As gouessej said, gl_FragCoord.xy will do the trick. However, it gives you the screen coordinates, not the coordinates of, say, your quad. If you're trying to (for example) make a horizontal gradient from 0.0 to 1.0, you would be better off using texture coordinates than relying on gl_FragCoord.

4) OpenCL is tricky to interact with OpenGL/GLSL and probably won't give you much of an improvement, unless your lighting calculations are extremely expensive.

It sounds like you are having trouble understanding the role of fragment and vertex shaders. You can read up on them here:

Pages: [1]
  ignore  |  Print  

EgonOlsen (79 views)
2018-06-10 19:43:48

EgonOlsen (59 views)
2018-06-10 19:43:44

EgonOlsen (78 views)
2018-06-10 19:43:20

DesertCoockie (261 views)
2018-05-13 18:23:11

nelsongames (159 views)
2018-04-24 18:15:36

nelsongames (158 views)
2018-04-24 18:14:32

ivj94 (901 views)
2018-03-24 14:47:39

ivj94 (162 views)
2018-03-24 14:46:31

ivj94 (813 views)
2018-03-24 14:43:53

Solater (177 views)
2018-03-17 05:04:08
Java Gaming Resources
by philfrei
2017-12-05 19:38:37

Java Gaming Resources
by philfrei
2017-12-05 19:37:39

Java Gaming Resources
by philfrei
2017-12-05 19:36:10

Java Gaming Resources
by philfrei
2017-12-05 19:33:10

List of Learning Resources
by elect
2017-03-13 14:05:44

List of Learning Resources
by elect
2017-03-13 14:04:45

SF/X Libraries
by philfrei
2017-03-02 08:45:19

SF/X Libraries
by philfrei
2017-03-02 08:44:05 is not responsible for the content posted by its members, including references to external websites, and other references that may or may not have a relation with our primarily gaming and game production oriented community. inquiries and complaints can be sent via email to the info‑account of the company managing the website of java‑
Powered by MySQL Powered by PHP Powered by SMF 1.1.18 | SMF © 2013, Simple Machines | Managed by Enhanced Four Valid XHTML 1.0! Valid CSS!