Comments (15)
unicomp21
commented on August 11, 2024
@snowymo @sebastianherscher any chance Dr. Perlin is available? ^^
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stegu
commented on August 11, 2024
Have you seen this short PDF of mine? With analytic gradients, normal
perturbation is really very simple. You just need to remember to scale the
gradient with the inner derivative of the 3D texture coordinates. I
reinvented this particular wheel before I found the reference, but first
publishing credit goes to Morten Mikkelsen (his PhD thesis from 2008).
https://weber.itn.liu.se/~stegu76/TNM084-2019/bumpmapping/bumpmapping.pdf
Some demo source code is in the link below. It's a file for Shadron, a very
convenient tool for shader programming experiments, but the ".shadron" file
is a plain text file with GLSL code included. It has code for recomputing
normals at the vertex level (displacement mapping) as well as at the
fragment level (bump mapping), using the same expressions for both. (Note
that the noise function is in its separate .glsl file, which may or may not
be identical to a file with the same name in the "webgl-noise" repo.)
https://weber.itn.liu.se/~stegu76/TNM084-2019/shadron
/Stefan G
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unicomp21
commented on August 11, 2024
Thanks @stegu !
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unicomp21
commented on August 11, 2024
@stegu is that the same as 5.6?
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stegu
commented on August 11, 2024
That article uses the same bump computation, yes, although it doesn't
explain how it works.
…On Mon, 10 May 2021, 00:38 John Davis, ***@***.***> wrote:
@stegu <https://github.com/stegu> is that the same as 5.6?
https://developer.nvidia.com/gpugems/gpugems/part-i-natural-effects/chapter-5-implementing-improved-perlin-noise
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unicomp21
commented on August 11, 2024
Thanks. Is there any way to get a 5th order interpolation between mesh.position's in the shader? When using webgl?
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stegu
commented on August 11, 2024
I am sorry for my mushy brain: the perturbation cretated by subtracting the
gradient from the normal without first projecting it to the surface tangent
plane is wrong. Looks OK but does not correspond to any analytical surface
normal. The projection described in my PDF and in Mikkelsen is the correct
way to do it, and it is only a small amount of extra work.
I don't quite understand what you mean by a 5th order interpolation of mesh
positions. The 5th order polynomial requires an input of 0..1, and that can
of course be achieved by texture coordinates or the like. The interpolation
is created in code, and if I'm not misremembering things, that is what my
implementations of "classic noise" are doing in the webgl-noise repo.
Analytic gradients are a lot less work than finite difference
approximations for simplex noise, but for classic noise the expressions for
the derivative get quite nasty. I would not recommend that.
…On Mon, 10 May 2021, 12:25 John Davis, ***@***.***> wrote:
Thanks. Is there any way to get a 5th order interpolation between
mesh.position's in the shader? When using webgl?
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unicomp21
commented on August 11, 2024
and that can of course be achieved by texture coordinates or the like
I get the gist of what's being said, but not sure I could implement it. Any links/recommendations for reading? Maybe I need to understand Barycentric coordinates better? What all do I encode in a vertex, so that I can recover the surrounding triangle, in the shader?
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stegu
commented on August 11, 2024
By "it" in "implementing it", you would be referring to what exactly? If
what I say below is a gross misunderstanding of the question, please ask
again.
Having parameters (0..1, 0..1) over a rectangle (two triangles) would
amount to setting vertex attributes (e.g "texture coordinates") for the
corners appropriately, let the vertex-to-fragment interpolation mechanism
interpolate that linearly (in a perspective correct manner), and compute
the 5th order polynomial weight (the "S-curve") in the fragment shader. The
built-in GLSL "smoothstep()" is a third order polynomial (3x^2 - 2x^3), so
the 5th order weight (6x^5 - 15x^4 + 10x^3) would need to be coded
explicitly.
Per-primitive surface parameters (u,v) in the range 0..1 are (were) a
staple of the Renderman standard, for every primitive except polygons, for
which (u,v) are zero everywhere and texture coordinates (s,t) need to be
specified explicitly for all vertices to handle surface mapping. Sadly,
polygons is currently all we have in OpenGL, so per-primitive texture
coordinates would be the way to go here. Note that local per-primitive
texture coordinates makes it impossible to do any longer runs of quads or
triangle strips/fans, because the texture coordinates for each shared
vertex is different from one quad to the next. Therefore, only single quads
or strips/fans of exactly two triangles are possible when sending the
primitives to OpenGL for drawing.
/Stefan
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unicomp21
commented on August 11, 2024
Exactly what I was looking for, thanks @stegu!
…On Mon, May 10, 2021 at 10:40 AM Stefan Gustavson ***@***.***> wrote:
By "it" in "implementing it", you would be referring to what exactly? If
what I say below is a gross misunderstanding of the question, please ask
again.
Having parameters (0..1, 0..1) over a rectangle (two triangles) would
amount to setting vertex attributes (e.g "texture coordinates") for the
corners appropriately, let the vertex-to-fragment interpolation mechanism
interpolate that linearly (in a perspective correct manner), and compute
the 5th order polynomial weight (the "S-curve") in the fragment shader. The
built-in GLSL "smoothstep()" is a third order polynomial (3x^2 - 2x^3), so
the 5th order weight (6x^5 - 15x^4 + 10x^3) would need to be coded
explicitly.
Per-primitive surface parameters (u,v) in the range 0..1 are (were) a
staple of the Renderman standard, for every primitive except polygons, for
which (u,v) are zero everywhere and texture coordinates (s,t) need to be
specified explicitly for all vertices to handle surface mapping. Sadly,
polygons is currently all we have in OpenGL, so per-primitive texture
coordinates would be the way to go here. Note that local per-primitive
texture coordinates makes it impossible to do any longer runs of quads or
triangle strips/fans, because the texture coordinates for each shared
vertex is different from one quad to the next. Therefore, only single quads
or strips/fans of exactly two triangles are possible when sending the
primitives to OpenGL for drawing.
/Stefan
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unicomp21
commented on August 11, 2024
@stegu see the distortion at the poles, on the sphere?
https://nodematerial-editor.babylonjs.com/#ND6Z9D#6
Think I'm not transforming the gradient properly? Any idea how I can fix it? Not sure how to transform into tangent space.
(using touchpad or mouse, scroll right pane down to bottom in order to see shader sphere w/ bumps)
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stegu
commented on August 11, 2024
I prefer not to transform to gradient space at all. World space 3D noise
makes that possible to avoid. See the PDF I linked to originally. It really
is a lot less cumbersome. Tangent space at the poles of a sphere with
lat-long mapping is not well defined -- a classic problem you just won't
have with 3D bump mapping.
…On Wed, 12 May 2021, 13:32 John Davis, ***@***.***> wrote:
@stegu <https://github.com/stegu> see the distortion at the poles, on the
sphere?
https://nodematerial-editor.babylonjs.com/#ND6Z9D#6
Think I'm not transforming the gradient properly? Any idea how I can fix
it? Not sure how to transform into tangent space.
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unicomp21
commented on August 11, 2024
@stegu I didn't realize that, thanks!
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stegu
commented on August 11, 2024
Sorry for the confusion. My PDF was written for my students, and it
includes a repetition of the tangent space method. I forgot to say "page 3
has the juicy bits".
/Stefan G
…On Mon, May 17, 2021 at 12:49 PM John Davis ***@***.***> wrote:
@stegu <https://github.com/stegu> I didn't realize that, thanks!
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unicomp21
commented on August 11, 2024
Thanks @stegu !
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Related Issues (20)
- 3D simplex noise exhibiting spacial artifacts not found in 2D simplex noise HOT 30
- Ugly artifacts in 2d simplex HOT 5
- Gradient to 3D Simplex Noise HOT 7
- Question: offsetting / seeding noise2D.glsl . HOT 1
- Periodicity along diagonal HOT 6
- Mention the range somewhere HOT 2
- Texture-intensive noise implementations HOT 4
- Period z is ignored for float pnoise(vec3 P, vec3 rep) HOT 5
- snoise(vec3) discontinuities HOT 9
- webgl HOT 2
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- Problems in Safari iOS on mediump HOT 25
- Use of implementation in art project HOT 10
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- Linker flags in Linux makefiles HOT 2
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