render3d: the ground's maps read through a page table of fine tiles over a coarse map (shaders)

terpage.glsl is the reference block (tpSlot, tpUV, terHeight, terHeightSmooth, terNormalXZ,
terOrtho, tpOrthoRes, tpOrthoLod), pasted by section into terrain.vert, terrain.frag,
tersun.frag, model.vert, grass.vert and grass.mesh. u_tp_on = 0 reads the old samplers with the
old coordinates and filtering; on, a resident tile is read at level 0 from u_tp_h / u_tp_nrm /
u_tp_ortho, anything else from the coarse map now bound under the old names. The B-splines use
the FULL map's texel and take every tap through the page, so a tile edge stays one surface;
blurred photograph reads (lod 1-2.5) stay on u_ortho with the level moved down by the coarse
map's ratio. The fragment stages drop their unused u_height. SPIR-V rebuilt: terrain programs
carry 23 samplers (21 in the fragment stage), up from 19.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packages/ludic.render3d/shaders/tersun.frag

@@ -11,10 +11,47 @@
 in vec3 v_wpos;
 in vec2 v_huv;
 out float o_sh;
-uniform sampler2D u_height;
+// no u_height here: the vertex stage reads the ground, and every declared sampler counts
+// against the stage's limit (MoltenVK) whether it is read or not
 // the baked terrain normal: x and z in RG16F, y rebuilt (a terrain normal always points up)
 uniform sampler2D u_ter_normal;
-vec3 terNormal(vec2 uv) { vec2 xz = texture(u_ter_normal, uv).rg;  return vec3(xz.x, sqrt(max(1.0 - dot(xz, xz), 0.0)), xz.y); }
+#define TP_FRAGMENT
+// terpage.glsl, pasted (the reference copy and its rules are there)
+// ---- the page table ----------------------------------------------------------------------
+#ifndef TP_HELPERS
+#define TP_HELPERS
+uniform sampler2D u_tp_page;   // R32F, a texel a tile: slot + 1, 0 = not resident
+uniform float u_tp_on;         // 1 while paging; 0 reads the whole maps exactly as before
+uniform vec4 u_tp_dims;        // tiles a side, height texels a tile, photo texels a tile, full height res
+// the layer holding a full-map uv, or -1: paging off, off the map, or not resident
+float tpSlot(vec2 uv) {
+  if (u_tp_on < 0.5 || uv.x < 0.0 || uv.y < 0.0 || uv.x >= 1.0 || uv.y >= 1.0) return -1.0;
+  ivec2 t = min(ivec2(floor(uv * u_tp_dims.x)), ivec2(int(u_tp_dims.x) - 1));
+  return texelFetch(u_tp_page, t, 0).r - 1.0;
+}
+// a full-map uv inside its tile's layer of k texels a side, past the one-texel border
+vec2 tpUV(vec2 uv, float k) { return (1.0 + fract(uv * u_tp_dims.x) * k) / (k + 2.0); }
+#endif
+// ---- the baked normal (x, z; y is rebuilt by the caller) ----------------------------------
+#ifndef TP_NORMAL
+#define TP_NORMAL
+uniform sampler2DArray u_tp_nrm;
+vec2 terNormalXZ(vec2 uv) {
+#ifdef TP_FRAGMENT
+  if (u_tp_on < 0.5) return texture(u_ter_normal, uv).rg;
+  // taken before the per-pixel branch: a neighbour on another tile must not decide the level
+  vec2 dx = dFdx(uv), dy = dFdy(uv);
+#endif
+  float s = tpSlot(uv);
+  if (s >= 0.0) return textureLod(u_tp_nrm, vec3(tpUV(uv, u_tp_dims.y), s), 0.0).rg;
+#ifdef TP_FRAGMENT
+  return textureGrad(u_ter_normal, uv, dx, dy).rg;
+#else
+  return textureLod(u_ter_normal, uv, 0.0).rg;
+#endif
+}
+#endif
+vec3 terNormal(vec2 uv) { vec2 xz = terNormalXZ(uv);  return vec3(xz.x, sqrt(max(1.0 - dot(xz, xz), 0.0)), xz.y); }
 uniform mat4 u_view;
 uniform float u_far_split;
 uniform float u_far_band;