• Announcements

    • khawk

      Download the Game Design and Indie Game Marketing Freebook   07/19/17

      GameDev.net and CRC Press have teamed up to bring a free ebook of content curated from top titles published by CRC Press. The freebook, Practices of Game Design & Indie Game Marketing, includes chapters from The Art of Game Design: A Book of Lenses, A Practical Guide to Indie Game Marketing, and An Architectural Approach to Level Design. The GameDev.net FreeBook is relevant to game designers, developers, and those interested in learning more about the challenges in game development. We know game development can be a tough discipline and business, so we picked several chapters from CRC Press titles that we thought would be of interest to you, the GameDev.net audience, in your journey to design, develop, and market your next game. The free ebook is available through CRC Press by clicking here. The Curated Books The Art of Game Design: A Book of Lenses, Second Edition, by Jesse Schell Presents 100+ sets of questions, or different lenses, for viewing a game’s design, encompassing diverse fields such as psychology, architecture, music, film, software engineering, theme park design, mathematics, anthropology, and more. Written by one of the world's top game designers, this book describes the deepest and most fundamental principles of game design, demonstrating how tactics used in board, card, and athletic games also work in video games. It provides practical instruction on creating world-class games that will be played again and again. View it here. A Practical Guide to Indie Game Marketing, by Joel Dreskin Marketing is an essential but too frequently overlooked or minimized component of the release plan for indie games. A Practical Guide to Indie Game Marketing provides you with the tools needed to build visibility and sell your indie games. With special focus on those developers with small budgets and limited staff and resources, this book is packed with tangible recommendations and techniques that you can put to use immediately. As a seasoned professional of the indie game arena, author Joel Dreskin gives you insight into practical, real-world experiences of marketing numerous successful games and also provides stories of the failures. View it here. An Architectural Approach to Level Design This is one of the first books to integrate architectural and spatial design theory with the field of level design. The book presents architectural techniques and theories for level designers to use in their own work. It connects architecture and level design in different ways that address the practical elements of how designers construct space and the experiential elements of how and why humans interact with this space. Throughout the text, readers learn skills for spatial layout, evoking emotion through gamespaces, and creating better levels through architectural theory. View it here. Learn more and download the ebook by clicking here. Did you know? GameDev.net and CRC Press also recently teamed up to bring GDNet+ Members up to a 20% discount on all CRC Press books. Learn more about this and other benefits here.
Sign in to follow this  
Followers 0
RenHoek

GL_FRAGMENT_SHADER_DERIVATIVE_HINT Is this useful anymore?

3 posts in this topic

GL_FRAGMENT_SHADER_DERIVATIVE_HINT

This hint apparently enables high quality ( or low quality ) derivatives in fragement shaders.

 

Does anyone know if this actually does _anything_ on modern hardware?

( eg Nvidia cards etc... )

 

Anybody know anything about this hint?

I see very little discussion about it anywhere on the internet.  :(

 

Thanks!

Ren

 

0

Share this post


Link to post
Share on other sites

In GPU Pro 2, there's a chapter called "Shader Amortization using Pixel Quad Message Passing", which explains how you can use the derivative functions to communicate between different instances of a pixel shader function, which allows for certain kinds of optimisations to be made.

I've personally used this technique to output to a R10_G10_B10_A2 render target, as if it was a full-resolution R10_G10_B10 target and a half-resolution A8 target, which was pretty useful.

 

Back to the point, this kind of inter-pixel communication is only possible with "high quality" derivatives. With "low quality" derivatives, only 3 out of every 4 pixels can communicate, with 1 out of 4 pixels being isolated and unable to talk to the others in it's "2x2 quad".

 

As far as I know, there's no way to query the hardware to see whether "low" or "high" quality derivatives are the default... You can only discover this by attempting to use one of these communication algorithms, and then reading the results to see if it worked or not.

I guess that if you wanted to use one of these techniques, you could first use the GL hint to kindly request "high" quality derivatives, and then test if your algorithm works, to increase your chances.

 

n.b. as of DX10/GL3 level hardware, all GPUs support both "low" and "high" quality modes (HLSL has different instructions for each, with the old "dFdx" type instructions being a "don't care" option).

2

Share this post


Link to post
Share on other sites


Back to the point, this kind of inter-pixel communication is only possible with "high quality" derivatives. With "low quality" derivatives, only 3 out of every 4 pixels can communicate, with 1 out of 4 pixels being isolated and unable to talk to the others in it's "2x2 quad".

 

Wow.   Ok.   Yes, this is was I was after.  :)

Acknowledgement that there actually _are_ different levels of derivative "quality" on modern hardware.

 

I help author a high-end tool which runs on the most modern of cards.  We're very quality concious ( rather than speed ).

So I'm going to set this hint to HighQuality regardless in our app from now on.

 

Question:

I know derivatives are used to select mip-map levels during texturing.

Do you know what happens if a polygon occupies only 1 pixel on screen?   ( or even 2x1 )

Any idea what the derivatives will give in that scenario?  And what mip-map level will be chosen?

 

Thanks!

Ren

0

Share this post


Link to post
Share on other sites

Do you know what happens if a polygon occupies only 1 pixel on screen?   ( or even 2x1 )
Any idea what the derivatives will give in that scenario?  And what mip-map level will be chosen?
 

The hardware is designed to always run the shader on 2x2 "quads" of pixels. If a triangle only covers part of a "quad", e.g. 1 pixel, then the GPU will actually execute the shader 4 times so that derivatives are still valid, but not actually use the results for 3 pixels.
Due to this design, extremely tesselated models (which cause pixel-sized triangles) actually reduce your pixel shading efficiency.
0

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now
Sign in to follow this  
Followers 0