4 ms·

Nowadays GPUs are able to convert between sRGB and linear automatically when reading and writing textures. There's no more excuse for incorrect rendering on mo

by panic 10y ago

Nowadays GPUs are able to convert between sRGB and linear automatically when reading and writing textures. There's no more excuse for incorrect rendering on modern hardware!

jblow 10y ago
Actually no, there are plenty of excuses, because this stuff gets super confusing and it's easy to make a mistake.
- kvark 10y ago
  How is The Witness doing w.r.t. gamma correctness? Any issues you can remember as an example of "super confusing" stuff?
  - jblow 10y ago
    If we made any mistakes, they are pretty small. What gets super confusing is that you have a bunch of different stuff flying around. You have textures in different formats and render targets in different formats (some are in sRGB, some are in HDR 16-bit floating-point, some are other random formats somewhere in-between). You need to set up your shader state to do the right thing for both the input texture and the render target, and the nuances of how to do this are going to change from system to system. Sometimes if you make a mistake it is easily spotted; other times it isn't. And then there are issues of vertex color, etc. Do you put your vertex colors in sRGB or linear space? Well, there are good reasons for either choice in different contexts. So maybe your engine provides both options. Well, now that's another thing for a programmer to accidentally get wrong sometimes. Maybe you want to introduce typechecked units to your floating-point colors to try and error-proof this, but we have not tried that and it might be annoying. All that said, everyone is about to rejigger their engines somewhat in order to be able to output to HDR TVs (we are in the process of doing this, and whereas it is not too terrible, it does involve throwing away some old stuff that doesn't make sense any more, and replace it by stuff that works a new way).
    - mentos 10y ago
      Off topic but curious to know your thoughts on Unreal Engine 4 and if you feel you could be as expressive in it as you would in your own proprietary engine?
      - pfranz 10y ago
        I'd love to hear a direct response, but here's[1] a quote from a few years ago (specifically mentioned Unity, not UE4, but I assume the sentiment is the same). I can't find it, but I was also reading an article a few days ago about why that person would choose to write their own engine over a third-party one. In that article (maybe it was the comments), they specifically called out the game mechanics of the The Witness and Braid as example of things traditional engines don't do very well. [1] https://www.reddit.com/r/Games/comments/282l0k/jonathan_blow_on_using_his_own_engine_i_would/ https://www.reddit.com/r/Games/comments/282l0k/jonathan_blow...
        mentos 10y ago
        That article is actually why I chose to use the word 'expressive' in my question! "..when I'm making these games, they're not just commercial products. They're expressive works that we're working very hard to make, and we want them to have as long of a lifetime as possible. So I would like this game to be relevant 20 years from now, 40 years from now. How do you do that? Well, you don't necessarily do that by building it on top of a very complicated system, that you don't own, that somebody else will cease to support at some point in the future." Given that UE4 is open source I wonder if he still has the same sentiment. As someone that has been working on a game in UE4 for 2.5 years the idea of rolling and supporting my own engine/tools is dizzying.
  - Negitivefrags 10y ago
    I don't work on The Witness, but here is an example of an issue I noticed just today on the game I work in. Look at the particles inside the pit at the bottom of the screen. http://imgur.com/BQjJD25 http://imgur.com/BQjJD25 Can you see what is wrong? Now take a look at what it used to look like: http://imgur.com/9z9b1cq http://imgur.com/9z9b1cq After seeing the correct version the problem is really obvious. The particular problem here is that at some point in the pipeline the colour of the particles were stored linearly instead of in sRGB. That results in the colour banding. A programmer who was working on the engine managed to accidentally break this, and the thing that really sucks about it is that the issue is really subtle and nobody noticed it for quite some time. Thankfully it didn't get to production before I noticed it, but that was complete chance. It could easily have gone out like that.
    - JesseMeyer 10y ago
      I love Path of Exile! Thanks for working hard at making it great!
- contravariant 10y ago
  Do everything in linear light, and convert to the proper gamma curve afterwards. It's almost the only way to be sure. If you want to be really sure you're correct do everything in the XYZ colour space and then finally convert to the correct RGB space. Which is pretty much unknown for most displays by the way, if you're lucky it's something similar to sRGB.

by panic 10y ago

Nowadays GPUs are able to convert between sRGB and linear automatically when reading and writing textures. There's no more excuse for incorrect rendering on modern hardware!

jblow 10y ago

Actually no, there are plenty of excuses, because this stuff gets super confusing and it's easy to make a mistake.

kvark 10y ago
How is The Witness doing w.r.t. gamma correctness? Any issues you can remember as an example of "super confusing" stuff?
- jblow 10y ago
  If we made any mistakes, they are pretty small. What gets super confusing is that you have a bunch of different stuff flying around. You have textures in different formats and render targets in different formats (some are in sRGB, some are in HDR 16-bit floating-point, some are other random formats somewhere in-between). You need to set up your shader state to do the right thing for both the input texture and the render target, and the nuances of how to do this are going to change from system to system. Sometimes if you make a mistake it is easily spotted; other times it isn't. And then there are issues of vertex color, etc. Do you put your vertex colors in sRGB or linear space? Well, there are good reasons for either choice in different contexts. So maybe your engine provides both options. Well, now that's another thing for a programmer to accidentally get wrong sometimes. Maybe you want to introduce typechecked units to your floating-point colors to try and error-proof this, but we have not tried that and it might be annoying. All that said, everyone is about to rejigger their engines somewhat in order to be able to output to HDR TVs (we are in the process of doing this, and whereas it is not too terrible, it does involve throwing away some old stuff that doesn't make sense any more, and replace it by stuff that works a new way).
  - mentos 10y ago
    Off topic but curious to know your thoughts on Unreal Engine 4 and if you feel you could be as expressive in it as you would in your own proprietary engine?
    - pfranz 10y ago
      I'd love to hear a direct response, but here's[1] a quote from a few years ago (specifically mentioned Unity, not UE4, but I assume the sentiment is the same). I can't find it, but I was also reading an article a few days ago about why that person would choose to write their own engine over a third-party one. In that article (maybe it was the comments), they specifically called out the game mechanics of the The Witness and Braid as example of things traditional engines don't do very well. [1] https://www.reddit.com/r/Games/comments/282l0k/jonathan_blow_on_using_his_own_engine_i_would/ https://www.reddit.com/r/Games/comments/282l0k/jonathan_blow...
      - mentos 10y ago
        That article is actually why I chose to use the word 'expressive' in my question! "..when I'm making these games, they're not just commercial products. They're expressive works that we're working very hard to make, and we want them to have as long of a lifetime as possible. So I would like this game to be relevant 20 years from now, 40 years from now. How do you do that? Well, you don't necessarily do that by building it on top of a very complicated system, that you don't own, that somebody else will cease to support at some point in the future." Given that UE4 is open source I wonder if he still has the same sentiment. As someone that has been working on a game in UE4 for 2.5 years the idea of rolling and supporting my own engine/tools is dizzying.
- Negitivefrags 10y ago
  I don't work on The Witness, but here is an example of an issue I noticed just today on the game I work in. Look at the particles inside the pit at the bottom of the screen. http://imgur.com/BQjJD25 http://imgur.com/BQjJD25 Can you see what is wrong? Now take a look at what it used to look like: http://imgur.com/9z9b1cq http://imgur.com/9z9b1cq After seeing the correct version the problem is really obvious. The particular problem here is that at some point in the pipeline the colour of the particles were stored linearly instead of in sRGB. That results in the colour banding. A programmer who was working on the engine managed to accidentally break this, and the thing that really sucks about it is that the issue is really subtle and nobody noticed it for quite some time. Thankfully it didn't get to production before I noticed it, but that was complete chance. It could easily have gone out like that.
  - JesseMeyer 10y ago
    I love Path of Exile! Thanks for working hard at making it great!
contravariant 10y ago
Do everything in linear light, and convert to the proper gamma curve afterwards. It's almost the only way to be sure. If you want to be really sure you're correct do everything in the XYZ colour space and then finally convert to the correct RGB space. Which is pretty much unknown for most displays by the way, if you're lucky it's something similar to sRGB.