Comments on: Encoding floats to RGBA, again http://aras-p.info/blog/2008/06/20/encoding-floats-to-rgba-again/ Random thoughts of a triangle pusher Fri, 09 Jan 2009 21:01:46 +0000 http://wordpress.org/?v=2.7 hourly 1 By: Aras Pranckevičius http://aras-p.info/blog/2008/06/20/encoding-floats-to-rgba-again/comment-page-1/#comment-12339 Aras Pranckevičius Tue, 01 Jul 2008 10:50:49 +0000 http://aras-p.info/blog/?p=181#comment-12339 @Pat: I think the difference is caused by the texture sampler differences. Even if GPUs do have floating point precision internally, regular 8 bit/channel textures are still sampled (and filtered!) at 8 bit precision, I guess for backwards compatibility reasons. Now, if there's a very slight change in how the sampling and filtering works, then differences like we have here might surface. That's my theory at least :) @Alex: not sure, I haven't actually tried that approach. @Pat: I think the difference is caused by the texture sampler differences. Even if GPUs do have floating point precision internally, regular 8 bit/channel textures are still sampled (and filtered!) at 8 bit precision, I guess for backwards compatibility reasons. Now, if there’s a very slight change in how the sampling and filtering works, then differences like we have here might surface. That’s my theory at least :)

@Alex: not sure, I haven’t actually tried that approach.

]]> By: Alex Lindsay http://aras-p.info/blog/2008/06/20/encoding-floats-to-rgba-again/comment-page-1/#comment-12338 Alex Lindsay Tue, 01 Jul 2008 10:22:30 +0000 http://aras-p.info/blog/?p=181#comment-12338 Hi, I had a go at this problem in my own special way. I'd be very interested in your opinions and results with the following (my post): http://www.gamedev.net/community/forums/topic.asp?topic_id=485186 It's certainly less elegant than the frac encode! Hi, I had a go at this problem in my own special way. I’d be very interested in your opinions and results with the following (my post):
http://www.gamedev.net/community/forums/topic.asp?topic_id=485186
It’s certainly less elegant than the frac encode!

]]> By: Pat Wilson http://aras-p.info/blog/2008/06/20/encoding-floats-to-rgba-again/comment-page-1/#comment-12252 Pat Wilson Tue, 24 Jun 2008 16:49:52 +0000 http://aras-p.info/blog/?p=181#comment-12252 Hmm, come to think of it, I don't think you could get enough texture addressing with FP16, so scratch that theory. Hmm, come to think of it, I don’t think you could get enough texture addressing with FP16, so scratch that theory.

]]> By: Pat Wilson http://aras-p.info/blog/2008/06/20/encoding-floats-to-rgba-again/comment-page-1/#comment-12251 Pat Wilson Tue, 24 Jun 2008 16:49:05 +0000 http://aras-p.info/blog/?p=181#comment-12251 This looks like it's related to the internal float representation of the card. I'm pulling numbers out of air, but I would guess that the early Radeons used FP16, x13-x19 used FP24, and HD series finally went to FP32. That would explain the large discrepancies between the early Radeons and the HD/GeForce/Intel cards. This looks like it’s related to the internal float representation of the card. I’m pulling numbers out of air, but I would guess that the early Radeons used FP16, x13-x19 used FP24, and HD series finally went to FP32. That would explain the large discrepancies between the early Radeons and the HD/GeForce/Intel cards.

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