Perspective-Correct Interpolation
andrewkchan.dev
Perspective-Correct Interpolation
1–10 of 13 posts
Re: Perspective-Correct Interpolation
#2An alternative explanation: https://gabrielgambetta.com/computer-graphics-from-scratch/1...
Re: Perspective-Correct Interpolation
#3I think computing 2D barycentric coordinates by inverting a 3x3 matrix whose last column is [1, 1, 1] is a bit wasteful.
The proper solution is this: https://gamedev.stackexchange.com/a/63203
Re: Perspective-Correct Interpolation
#4Reminded me of Quake's trick[1] of calculating the perspective correction every 16 pixels, as you then effectively got it for free on a Pentium processor.
Re: Perspective-Correct Interpolation
#5Reminded me of Quake's trick[1] of calculating the perspective correction every 16 pixels, as you then effectively got it for free on a Pentium processor. [1]: https://www.bluesnews.com/abrash/chap68.shtml
I remembered the same. Perspective correction needs a division operation for each pixel and while drawing a scanline, calculating it every 16 pixels and linearly interpolating between them make a huge speed difference.
Re: Perspective-Correct Interpolation
#6Reminded me of Quake's trick[1] of calculating the perspective correction every 16 pixels, as you then effectively got it for free on a Pentium processor. [1]: https://www.bluesnews.com/abrash/chap68.shtml
I remember that Descent, released earlier, had used the same trick.
Re: Perspective-Correct Interpolation
#7This is a fascinating topic, especially when considering how this was achieved back in the days. We now take it for granted, but this was not a simple feature to have in your game in 199x ( xFor anyone interested: I have a detailed write up on the topic here in the context of 1990s renderers https://github.com/sylefeb/tinygpus/tree/main?tab=readme-ov-... ; a video discussing texture mapping with a hardware twist https://youtu.be/2ZAIIDXoBis?si=MvQXH2ltqWmvFMdt&t=1072 ; and have a shadertoy to compare perspective correct texture mapping on/off https://www.shadertoy.com/view/ftKSzR
Re: Perspective-Correct Interpolation
#8The funny thing about this was that by the time you'd finished a 10 hour session of Tomb Raider you got used to the effect, so reality looked weirdly distorted for a while after.
Re: Perspective-Correct Interpolation
#9Reminded me of Quake's trick[1] of calculating the perspective correction every 16 pixels, as you then effectively got it for free on a Pentium processor. [1]: https://www.bluesnews.com/abrash/chap68.shtml
I remember that Descent, released earlier, had used the same trick.
It turns out we all could count cycles.
Seriously, this keeps getting overhyped as some gigantic insight when it was really just a consequence of the Pentium having been released in 1993. And with the Pentium, you got both reliable FPU availability (none of the 486SX pain), and the cycle count for FDIV dropped by almost 50% (73->39 IIRC)
Everybody doing 3d gfx knew you needed a perspective divide and was looking at ways to do that cheaply. Interpolation + a long-latency instruction that doesn't block the main pipelines is a fairly straightforward answer.
Re: Perspective-Correct Interpolation
#10Earlier quoted context omitted.
I remember that Descent, released earlier, had used the same trick.
It turns out we all could count cycles. Seriously, this keeps getting overhyped as some gigantic insight when it was really just a consequence of the Pentium having been released in 1993. And with the Pentium, you got both reliable FPU availability (none of the 486SX pain), and the cycle count for FDIV dropped by almost 50% (73->39 IIRC) Everybody doing 3d gfx knew you needed a perspective divide and was looking at w…
I seem to recall reading about it in one of the demo code articles floating about at the time, similar to this one[1]. But Quake is the one that stuck with me for some reason, and it's easy to link to.
[1]: https://www.lysator.liu.se/~mikaelk/doc/perspectivetexture/