refactor: move common/shaders/ to src/shaders/

Relocates shared WGSL shaders under src/ where all source code lives,
eliminating the top-level common/ directory.

- Update asset references in workspaces/main/assets.txt and workspaces/test/assets.txt
- Update docs: PROJECT_CONTEXT.md, ARCHITECTURE.md, WORKSPACE_SYSTEM.md, SHADER_REUSE_INVESTIGATION.md

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

1 files changed, 66 insertions, 0 deletions

diff --git a/src/shaders/render/raymarching.wgsl b/src/shaders/render/raymarching.wgsl
new file mode 100644
index 0000000..2d6616d
--- /dev/null
+++ b/src/shaders/render/raymarching.wgsl
@@ -0,0 +1,66 @@
+// Common functions for Signed Distance Field (SDF) raymarching.
+//
+// Required user-defined functions:
+//   - df(vec3f) -> f32
+//       Distance field for single-pass rendering (rayMarch, normal, shadow)
+//
+// For two-pass rendering with object IDs, see raymarching_id.wgsl
+//
+// Provided constants:
+//   TOLERANCE, MAX_RAY_LENGTH, MAX_RAY_MARCHES, NORM_OFF
+
+const TOLERANCE: f32 = 0.0005;
+const MAX_RAY_LENGTH: f32 = 20.0;
+const MAX_RAY_MARCHES: i32 = 80;
+const NORM_OFF: f32 = 0.005;
+
+// Computes the surface normal of the distance field at a point `pos`.
+fn normal(pos: vec3f) -> vec3f {
+  let eps = vec2f(NORM_OFF, 0.0);
+  var nor: vec3f;
+  nor.x = df(pos + eps.xyy) - df(pos - eps.xyy);
+  nor.y = df(pos + eps.yxy) - df(pos - eps.yxy);
+  nor.z = df(pos + eps.yyx) - df(pos - eps.yyx);
+  return normalize(nor);
+}
+
+// Performs the raymarching operation.
+// Returns the distance along the ray to the surface, or MAX_RAY_LENGTH if no surface is hit.
+fn rayMarch(ro: vec3f, rd: vec3f, tmin: f32) -> f32 {
+  var t = tmin;
+  for (var i = 0; i < MAX_RAY_MARCHES; i++) {
+    if (t > MAX_RAY_LENGTH) {
+      t = MAX_RAY_LENGTH;
+      break;
+    }
+    let d = df(ro + rd * t);
+    if (d < TOLERANCE) {
+      break;
+    }
+    t += d;
+  }
+  return t;
+}
+
+// Computes a soft shadow for a given point.
+fn shadow(lp: vec3f, ld: vec3f, mint: f32, maxt: f32) -> f32 {
+  let ds = 1.0 - 0.4;
+  var t = mint;
+  var nd = 1e6;
+  let soff = 0.05;
+  let smul = 1.5;
+  let MAX_SHD_MARCHES = 20;
+
+  for (var i = 0; i < MAX_SHD_MARCHES; i++) {
+    let p = lp + ld * t;
+    let d = df(p);
+    if (d < TOLERANCE || t >= maxt) {
+      let sd = 1.0 - exp(-smul * max(t / maxt - soff, 0.0));
+      return select(mix(sd, 1.0, smoothstep(0.0, 0.025, nd)), sd, t >= maxt);
+    }
+    nd = min(nd, d);
+    t += ds * d;
+  }
+  let sd = 1.0 - exp(-smul * max(t / maxt - soff, 0.0));
+  return sd;
+}