i nerd sniped myself tonight and i imagine the NSA operative who is assigned to me is very confused by the increasingly erratic and frustrated google searches for HOW DO I CALCULATE THE MOON WHERE IS THE MOON

[aeva@mastodon.gamedev.place]

@jon_valdes @dotstdy blessedly I'm planning on doing this on the cpu, but

[jon_valdes@mastodon.gamedev.place]

@aeva @dotstdy if you want to see this in action, open this shadertoy on a few different GPUs and compare the output on each. Particularly fun if you have a pre-Arc Intel GPU...

https://www.shadertoy.com/view/dtlyD8

[aeva@mastodon.gamedev.place]

@jon_valdes @dotstdy my laptop has a recent-ish Xe gpu

[aeva@mastodon.gamedev.place]

@jon_valdes @dotstdy it's bizarre seeing my 10 year old telephone's mali do better at... anything at all

[aeva@mastodon.gamedev.place]

@jon_valdes @dotstdy though I guess the corner the intel case is cutting is where the slope starts to level out so I guess that makes sense. are CPU trig functions just as bad?

[aeva@mastodon.gamedev.place]

@jon_valdes @dotstdy would mollytime get a warmer, fuller sound if i switched to expensive software sine waves :3

[dotstdy@mastodon.social]

@aeva @jon_valdes generally cpu trig is not so bad, but does vary between platforms if you're just calling the c stdlib functions (but we're talking differences of 1 ulp or so). so yes, absolutely you can get a warmer fuller soundstage by switching to a different sin.

[jon_valdes@mastodon.gamedev.place]

@aeva @dotstdy Yup! I was using trig to calculate screen positions for the stars. And as the skydome rotates, when the sin/cos of some stars happened to cross those bright lines you're seeing, they'd first slow down, and then jump over a very specific line in the sky. Was great

[aeva@mastodon.gamedev.place]

@jon_valdes @dotstdy

[aeva@mastodon.gamedev.place]

@dotstdy @jon_valdes maybe I'll call the expensive exact soft sin oscillator "gold plated sin"

[demofox@mastodon.gamedev.place]

@aeva @dotstdy @jon_valdes start a new genre "deca-dance"

[aeva@mastodon.gamedev.place]

@demofox @dotstdy @jon_valdes well so far I can't tell the difference by ear between the soft sin and the double precision sin that clang gives me

[aeva@mastodon.gamedev.place]

@demofox @dotstdy @jon_valdes assuming I didn't screw anything up adapting Jon's shader toy, the 30 iteration soft sin also has the surprising property of being able to clip out of the expected -1.0 to 1.0 output range https://github.com/Aeva/mollytime/blob/af58e9237903856b6193a116ae6408038dc47d4a/src/patch.cpp#L319

[tomf@mastodon.gamedev.place]

@aeva @demofox @dotstdy @jon_valdes There's lots of versions of CPU sin/cos as well. The fastest is basically identical to the GPU one - about 12 bits of precision, IIRC. Then they do iteration internally if you want higher precision. There's no magic - everything costs!

As you noticed, sometimes it's better not to call sin-vs-cos, because you're not guaranteed to get magnitude 1.0. In those cases it's better to get sin and derive the other by doing sqrt(1-sin^2).