More 2021-07-27-procedural-meshes rambling

content/posts/2021-07-27-procedural-meshes/index.org

@@ -38,14 +38,23 @@ way to learn things in a new language.  (I think it's similar to
 I've also played around in 3D graphics, particularly raytracing, since
 about 1999 in PolyRay and POV-Ray... though my [[../../images/portfolio/1999-12-22-table.jpg][few surviving]] [[../../images/portfolio/1999-12-21-moo.jpg][renders
 from 1999]] are mostly garbage.  POV-Ray is probably what led me to
-learn about things like implicit surfaces, parametric surfaces, and
+learn about things like procedural geometry and textures, especially
-procedural geometry - its scene language is full of constructs for
+implicit surfaces and parametric surfaces, as its scene language is
-that.  Naturally, this led me to wonder how I might extend Context
+full of constructs for that.  The images below are some of my POV-Ray
-Free's model to work more generally with 3D geometry, and let me use
+scenes from way back in 2005, with the first two done completely with
-it to produce procedural geometry.
+its implicit surfaces.
 
-# TODO: Link to some POV-Ray scenes here with implicit & parametric
+{{< gallery >}}
-# surfaces?
+    {{< figure page="images" resource="portfolio/2005-07-05-spiral-isosurface2.jpg">}}
+    {{< figure page="images" resource="portfolio/2005-07-08-vaguely-celtic-metalwork.jpg">}}
+    {{< figure page="images" resource="portfolio/2005-08-23-shear6.jpg">}}
+{{< /gallery >}}
+
+Naturally, this led me to wonder how I might extend Context Free's
+model to work more generally with 3D geometry, and let me use it to
+produce procedural geometry.
+
+# ../2011-02-07-blender-from-a-recovering-pov-ray-user ?
 
 [[http://structuresynth.sourceforge.net/index.php][Structure Synth]] of course already exists, and is a straightforward
 generalization of Context Free's model to 3D (thank you to Mikael
@@ -69,9 +78,9 @@ was trying to work with it:
     {{< figure page="images" resource="placeholder/appleseed_spiral_thing.jpg">}}
 {{< /gallery >}}
 
-That's a "Hello World" tier design I try out when something gives me
+That's a "Hello World"-tier design I try out when something gives me
 geometric transforms and recursion.  The first image (the Blender one)
-snhould show the bits of unconnected and half-connected and
+should show the bits of unconnected and half-connected and
 self-intersecting geometry - that is what I wanted to work around.
 You can look at this and say, "That really makes no difference, and
 Structure Synth is capable of anything you /practically/ want to
@@ -98,27 +107,49 @@ this geometry is even fairly mild.  This really isn't surprising, as
 tools like this were made for practical applications in CAD, and not
 so much for my silly explorations in generative art.
 
-But wait! Implicit surfaces handle almost all of this well! (Or call
+But wait! *Implicit surfaces* handle almost all of this well! (Or see
-them one of the many related-but-not-identical things around this,
+any of the related-but-not-identical things around this, e.g. [[https://en.wikipedia.org/wiki/Function_representation][F-Reps]]
-e.g. [[https://en.wikipedia.org/wiki/Function_representation][F-Reps]] or distance bounds or [[https://en.wikipedia.org/wiki/Signed_distance_function][SDFs]] or isosurfaces...) They express
+or distance bounds or distance fields or [[https://en.wikipedia.org/wiki/Signed_distance_function][SDFs]] or isosurfaces...) They
-[[https://en.wikipedia.org/wiki/Constructive_solid_geometry][CSG]] operations, they can be rendered directly on the GPU via shaders,
+express [[https://en.wikipedia.org/wiki/Constructive_solid_geometry][CSG]] operations, they can be rendered directly on the GPU via
-operations like blending shapes or twisting them are easy... for more
+shaders, operations like blending shapes or twisting them are easy,
-on this, see [[http://blog.hvidtfeldts.net/][Syntopia]] again, or nearly anything by [[https://iquilezles.org/][Inigo Quilez]], or
+and when generalized to things like distance functions, they can be
-look up raymarching and sphere tracing, or see [[https://ntopology.com/][nTopology]], or Matt
+used to render shapes like fractals that are infinitely complex and
+lack an analytical formula for the surface, like the [[https://www.skytopia.com/project/fractal/mandelbulb.html][Mandelbulb]]. For
+more on this, see [[http://blog.hvidtfeldts.net/][Syntopia]] again, or nearly anything by [[https://iquilezles.org/][Inigo Quilez]],
+or look up raymarching and sphere tracing, or see [[https://ntopology.com/][nTopology]], or Matt
 Keeter's work with [[https://www.libfive.com/][libfive]] and [[https://www.mattkeeter.com/research/mpr/][MPR]].  They're pure magic, they're
 wonderfully elegant, and I'll probably have many other posts on them.
 (TODO: Link to my CS6460 stuff)
 
-However, there is one big issue: turning implicit surfaces to good
+Many renderers can render implicit surfaces directly.  POV-Ray is one
-meshes for rendering /is a huge pain/.  While many renderers can
+of them - see [[https://www.povray.org/documentation/view/3.6.1/300/][Isosurface Object]] which a few of my examples above
-handle implicit surfaces directly, Blender's renderers cannot. I will
+use. The appleseed renderer can sort of do it via a [[https://github.com/appleseedhq/appleseed/blob/master/sandbox/examples/cpp/distancefieldobject/distancefieldobject.cpp][custom object via
-have other posts going into more detail on this subject, but for now,
+a plugin]].  [[https://www.shadertoy.com/][Shadertoy]] is also full of user-created examples of ad-hoc
-take it on faith.  If you don't believe me, believe Matt Keeter in
+realtime rendering of implicit surfaces, mostly in the form of sphere
-[[https://www.mattkeeter.com/research/mpr/keeter_mpr20.pdf][his paper]] when he says in a rather understated way, "Having implemented
+tracers, done completely in [[https://en.wikipedia.org/wiki/OpenGL_Shading_Language][GLSL]].  Keeter's work on [[https://www.mattkeeter.com/research/mpr/][MPR]] is all about
-many of these algorithms, we've found it extremely difficult to make
+realtime rendering of this sort in a much more scalable way.
-them robust." This is why I did not try to use implicit surfaces for
+
-this project.
+# TODO: Why not move the spiral isosurface from POV-Ray here, and give
-(TODO: Make those posts.)
+# its formula and explain a little? Or - should this be for another
+# post?
+
+Many renderers don't handle implicit surfaces at all.  Blender's
+renderers, [[https://www.cycles-renderer.org/][Cycles]] and [[https://docs.blender.org/manual/en/latest/render/eevee/introduction.html][Eevee]], are among them.  Using implicit surfaces
+there means converting them to a form of geometry that Blender /can/
+handle - typically a polygon mesh.
+
+This leads to a pretty big issue: turning implicit surfaces to good
+meshes for rendering /is a huge pain/.  If you don't believe me,
+believe Matt Keeter in [[https://www.mattkeeter.com/research/mpr/keeter_mpr20.pdf][his paper]] when he says, "There is significant
+literature on converting implicit surfaces into meshes for
+visualization. Having implemented many of these algorithms, we've
+found it extremely difficult to make them robust."  I'd love to tell
+you that I saw this advice before wasting my time trying to turn
+implicit surfaces to meshes, first with various libraries and then
+with ad-hoc conversions and optimizations of my own, but I didn't.  I
+may have other posts talking about my failures here, but for now, take
+it on faith that this is why I gave up trying to use implicit surfaces
+for this project.  (TODO: Make those posts.)
 
 With these limitations in mind, around 2018 June I had started jotting
 some ideas down.  The gist is that I wanted to create