ref: af0338b7ba4d9c6011caaf10f4fd363da4651a42
author: rodri <rgl@antares-labs.eu>
date: Fri Aug 30 16:31:32 EDT 2024
initial dump of ideas.
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+# semblance
+
+Semblance wants to be a shading language.
+
+The idea is for it to have a translator that turns semblance shaders
+into C that can be used with [libgraphics][1], and later turn it into a
+VM that runs in [renderfs][2].
+
+It's largely influenced by the [RSL][3] and [GLSL][4] languages.
+
+## Syntax
+
+ - declare and use custom structs
+ - new types
+ vector → Point3 (x,y,z,0)
+ point → Point3 (x,y,z,w)
+ point2 → Point2 (x,y,w)
+ pointN → PointN (x,y,[w|z,w]) | N ∈ {2,3} ???+ normal → Point3 (x,y,z,0) | {x,y,z} ∈ [0,1]+ color → Color
+ matrix → Matrix[23] ???
+ quat → Quaternion
+ - new operators
+ Matrix3 m, n;
+ Point3 a, b;
+ double s;
+
+ b = b * a; /* b = modulatept3(a, b); */
+ b = b * s; /* b = mulpt3(b, s); */
+ b = b * m; /* xform3(b, m); */
+ b = b × a; /* b = crossvec3(b, a); */
+ b = b · a; /* b = dotvec3(b, a); */
+ m = m * n; /* mulm3(m, n); */
+
+ Matrix3 m2:
+ m2 = m * n; /* identity3(m2); mulm3(m2, m); mulm3(m2, n); */
+ /* alt.: memmove(m2, m, 4*4*sizeof(double)); mulm3(m2, n); */
+ - function polymorphism
+ Point3 a, b;
+ double c, d;
+
+ a = lerp(a, b, 0.4); /* lerp3(2); */
+ c = lerp(c, d, 0.1); /* flerp(2); */
+
+ Texture *tex;
+ Cubemap *cm;
+ Point3 dir;
+ Point2 uv;
+ Color c;
+
+ c = sample(tex, uv, nearest); /* sampletexture(2) */
+ c = sample(cm, dir, bilinear); /* samplecubemap(2) */
+
+ int a, b;
+ double c, d;
+ Point3 p0, p1;
+
+ a = min(a, b);
+ c = min(c, d);
+ p0 = min(p0, p1); /* component-wise */
+ - stage-dependent shader parameters
+ - vertex
+ | in shader | in libgraphics |
+ +--------------------------------+
+ position → sp->v->p
+ normal → sp->v->n
+ color → sp->v->c
+ uv → sp->v->uv
+ material → sp->v->mtl
+ tangent → sp->v->tangent
+ <attr> → sp->v->attrs["<attr>"]
+ - fragment
+ | in shader | in libgraphics |
+ +--------------------------------+
+ position → sp->v.p
+ color → sp->v.c
+ <attr> → sp->v.attrs["<attr>"]
+ - swizzles
+ Point3 p;
+ Color c;
+
+ c.rgba = p.xyzw;
+ c.rgb = p.xyz;
+ p.zyx = c.rgb;
+ - builtins
+ In the following cases the absent parameters are replaced by:
+
+ Entity* → sp->su->entity
+ Camera* → sp->su->camera
+ Framebuf* → sp->su->fb
+
+ when translated for libgraphics.
+
+ Point3 model2world(Point3) /* Point3 model2world(Entity*, Point3); */
+ Point3 world2vcs(Point3) /* Point3 world2vcs(Camera*, Point3); */
+ Point3 vcs2clip(Point3); /* Point3 vcs2clip(Camera*, Point3); */
+ Point3 world2clip(Point3); /* Point3 world2clip(Camera*, Point3); */
+ Point3 clip2ndc(Point3); /* Point3 clip2ndc(Point3); */
+ Point3 ndc2viewport(Point3); /* Point3 ndc2viewport(Framebuf*, Point3); */
+ Point3 viewport2ndc(Point3); /* Point3 viewport2ndc(Framebuf*, Point3); */
+ Point3 ndc2vcs(Point3); /* Point3 ndc2vcs(Camera*, Point3); */
+ Point3 viewport2vcs(Point3); /* Point3 viewport2vcs(Camera*, Point3); */
+ Point3 vcs2world(Point3); /* Point3 vcs2world(Camera*, Point3); */
+ Point3 viewport2world(Point3); /* Point3 viewport2world(Camera*, Point3); */
+ Point3 world2model(Point3); /* Point3 world2model(Entity*, Point3); */
+
+## References
+
+[1]: https://shithub.us/rodri/libgraphics
+[2]: https://shithub.us/rodri/renderfs
+[3]: https://renderman.pixar.com/resources/RenderMan_20/shadingLanguage.html
+[4]: https://www.khronos.org/files/opengles_shading_language.pdf