Atmosphere LUT parameterization improvements #17555
Conversation
|
Welcome, new contributor! Please make sure you've read our contributing guide and we look forward to reviewing your pull request shortly ✨ |
alice-i-cecile
added
C-Feature
orbital.sunset.mp4 |
ecoskey
added
S-Ready-For-Final-Review
|
|
|
After some more discussions, this discovery points to an issue in how the sample points are calculated. Therefore in order to remove the 0.5 texel offset in the sampling function, we need to fix the math that compute the sample positions. I will work on that tomorrow. |
ecoskey
added
S-Waiting-on-Author
|
I've corrected the quadratic sampling in the sky view lut, reverted that to linear to recover the numerical accuracy. I've added a constant variable for the I posted the test scene and the raymarched reference code in the |
| // where in the segment that sample is taken (0.0 = start, 0.5 = middle, 1.0 = end). | ||
| // We use 0.3 to sample closer to the start of each segment, which better approximates | ||
| // the exponential falloff of atmospheric density. | ||
| const MIDPOINT_RATIO: f32 = 0.3; |
There was a problem hiding this comment.
This could be exposed as a uniform variable, since it can differ depending on the scale height of the scatterers in the atmosphere.
There was a problem hiding this comment.
possibly, if it doesn't add more complexity to the user-facing api. Alternatively we could also just do the integration differently, for example piecewise linearly or quadratically (trapezoid rule vs simpson's rule)
alice-i-cecile
added
S-Ready-For-Final-Review
|
Okay great! I think I've addressed everything and this PR is ready for the merge queue @alice-i-cecile |
|
Great cleanup and bug fixes; thanks a ton <3 |
# Objective - Fix the atmosphere LUT parameterization in the aerial -view and sky-view LUTs - Correct the light accumulation according to a ray-marched reference - Avoid negative values of the sun disk illuminance when the sun disk is below the horizon ## Solution - Adding a Newton's method iteration to `fast_sqrt` function - Switched to using `fast_acos_4` for better precision of the sun angle towards the horizon (view mu angle = 0) - Simplified the function for mapping to and from the Sky View UV coordinates by removing an if statement and correctly apply the method proposed by the [Hillarie paper](https://sebh.github.io/publications/egsr2020.pdf) detailed in section 5.3 and 5.4. - Replaced the `ray_dir_ws.y` term with a shadow factor in the `sample_sun_illuminance` function that correctly approximates the sun disk occluded by the earth from any view point ## Testing - Ran the atmosphere and SSAO examples to make sure the shaders still compile and run as expected. --- ## Showcase <img width="1151" alt="showcase-img" src="https://github.com/user-attachments/assets/de875533-42bd-41f9-9fd0-d7cc57d6e51c" /> --------- Co-authored-by: Emerson Coskey <[email protected]>
# Objective - Fix the atmosphere LUT parameterization in the aerial -view and sky-view LUTs - Correct the light accumulation according to a ray-marched reference - Avoid negative values of the sun disk illuminance when the sun disk is below the horizon ## Solution - Adding a Newton's method iteration to `fast_sqrt` function - Switched to using `fast_acos_4` for better precision of the sun angle towards the horizon (view mu angle = 0) - Simplified the function for mapping to and from the Sky View UV coordinates by removing an if statement and correctly apply the method proposed by the [Hillarie paper](https://sebh.github.io/publications/egsr2020.pdf) detailed in section 5.3 and 5.4. - Replaced the `ray_dir_ws.y` term with a shadow factor in the `sample_sun_illuminance` function that correctly approximates the sun disk occluded by the earth from any view point ## Testing - Ran the atmosphere and SSAO examples to make sure the shaders still compile and run as expected. --- ## Showcase <img width="1151" alt="showcase-img" src="https://github.com/user-attachments/assets/de875533-42bd-41f9-9fd0-d7cc57d6e51c" /> --------- Co-authored-by: Emerson Coskey <[email protected]>
Objective
Solution
fast_sqrtfunctionfast_acos_4for better precision of the sun angle towards the horizon (view mu angle = 0)ray_dir_ws.yterm with a shadow factor in thesample_sun_illuminancefunction that correctly approximates the sun disk occluded by the earth from any view pointTesting
Showcase