feat(editor): add --gen-texture-carbon fiber-weave pattern

57th procedural texture: 2x2 cell pattern where alternating
cells hold horizontal vs vertical fiber segments. Each
segment gets a sin² brightness profile across its
perpendicular axis — 0 at the segment edge, peak at center —
giving the rounded highlight of a real woven fiber bundle.

Cell-pair parity (cx + cy) % 2 determines orientation, so
adjacent cells always alternate weave direction in both X
and Y. Reads as the unmistakable carbon-fiber checkerboard
even at small scales.

Useful for sci-fi armor, sleek tech panels, vehicle bodies,
ritual obsidian inlays, dwarven runeplate accents — any
"machined composite" surface where flat dark grey would
read as plain plastic.

Default 12-pixel cell at 256x256 reads cleanly with about
21 visible weave segments per side.

tools/editor/cli_arg_required.cpp

@@ -90,6 +90,7 @@ const char* const kArgRequired[] = {
     "--gen-texture-rope", "--gen-texture-caustics",
     "--gen-texture-starburst", "--gen-texture-studs",
     "--gen-texture-moss", "--gen-texture-woodgrain",
+    "--gen-texture-carbon",
     "--validate-glb", "--info-glb", "--info-glb-tree", "--info-glb-bytes",
     "--validate-jsondbc", "--check-glb-bounds", "--validate-stl",
     "--validate-png", "--validate-blp",

tools/editor/cli_gen_texture.cpp

@@ -4235,6 +4235,75 @@ int handleKnit(int& i, int argc, char** argv) {
     return 0;
 }
 
+int handleCarbon(int& i, int argc, char** argv) {
+    // Carbon-fiber weave: 2x2 cells where alternating cells hold
+    // horizontal vs vertical fiber segments. Each segment has a
+    // sin² brightness profile across its perpendicular axis,
+    // simulating the rounded highlight on a real woven fiber bundle.
+    // Useful for sci-fi armor, sleek tech panels, hi-tech vehicle
+    // bodies, ritual obsidian inlays, or any "machined composite"
+    // surface where a flat color would read as plastic.
+    std::string outPath = argv[++i];
+    std::string bgHex   = argv[++i];
+    std::string fibHex  = argv[++i];
+    int cellSize = 12;
+    int W = 256, H = 256;
+    parseOptInt(i, argc, argv, cellSize);
+    parseOptInt(i, argc, argv, W);
+    parseOptInt(i, argc, argv, H);
+    if (W < 1 || H < 1 || W > 8192 || H > 8192 ||
+        cellSize < 2 || cellSize > 1024) {
+        std::fprintf(stderr,
+            "gen-texture-carbon: invalid dims (W/H 1..8192, "
+            "cellSize 2..1024)\n");
+        return 1;
+    }
+    uint8_t br_, bg_, bb_, fr, fg, fb_;
+    if (!parseHex(bgHex, br_, bg_, bb_) ||
+        !parseHex(fibHex, fr, fg, fb_)) {
+        std::fprintf(stderr,
+            "gen-texture-carbon: bg or fiber hex color is invalid\n");
+        return 1;
+    }
+    std::vector<uint8_t> pixels(static_cast<size_t>(W) * H * 3, 0);
+    const float pi = 3.14159265358979f;
+    const float invCell = 1.0f / cellSize;
+    for (int y = 0; y < H; ++y) {
+        int cy = y / cellSize;
+        int ly = y - cy * cellSize;
+        for (int x = 0; x < W; ++x) {
+            int cx = x / cellSize;
+            int lx = x - cx * cellSize;
+            // (cx + cy) parity determines fiber orientation.
+            // Brightness profile is sin² of the perpendicular
+            // local coord normalized to [0, π].
+            bool horiz = ((cx + cy) & 1) == 0;
+            float perp = horiz ? (ly * invCell) : (lx * invCell);
+            float s = std::sin(perp * pi);
+            float t = s * s;        // 0..1, peak at center
+            uint8_t r = static_cast<uint8_t>(br_ + t * (fr - br_));
+            uint8_t g = static_cast<uint8_t>(bg_ + t * (fg - bg_));
+            uint8_t b = static_cast<uint8_t>(bb_ + t * (fb_ - bb_));
+            size_t idx = (static_cast<size_t>(y) * W + x) * 3;
+            pixels[idx + 0] = r;
+            pixels[idx + 1] = g;
+            pixels[idx + 2] = b;
+        }
+    }
+    if (!stbi_write_png(outPath.c_str(), W, H, 3,
+                        pixels.data(), W * 3)) {
+        std::fprintf(stderr,
+            "gen-texture-carbon: stbi_write_png failed for %s\n",
+            outPath.c_str());
+        return 1;
+    }
+    std::printf("Wrote %s\n", outPath.c_str());
+    std::printf("  size       : %dx%d\n", W, H);
+    std::printf("  bg/fiber   : %s / %s\n", bgHex.c_str(), fibHex.c_str());
+    std::printf("  weave cell : %d\n", cellSize);
+    return 0;
+}
+
 int handleWoodgrain(int& i, int argc, char** argv) {
     // Wood-end grain: concentric annual rings centered slightly
     // outside the image (so the texture shows arcs sweeping across
@@ -5058,6 +5127,7 @@ constexpr TextureEntry kTextureTable[] = {
     {"--gen-texture-studs",          3, handleStuds},
     {"--gen-texture-moss",           3, handleMoss},
     {"--gen-texture-woodgrain",      3, handleWoodgrain},
+    {"--gen-texture-carbon",         3, handleCarbon},
 };
 }  // namespace
 

tools/editor/cli_help.cpp

@@ -147,6 +147,8 @@ void printUsage(const char* argv0) {
     std::printf("                         Moss: irregular spots scattered on a hash-jittered grid (forest floor / weathered stone / swamp)\n");
     std::printf("  --gen-texture-woodgrain <out.png> <lightHex> <darkHex> [spacing] [seed] [W H]\n");
     std::printf("                         Woodgrain: concentric annual rings centered off-image with per-ring jitter (end-cut wood)\n");
+    std::printf("  --gen-texture-carbon <out.png> <bgHex> <fiberHex> [cellSize] [W H]\n");
+    std::printf("                         Carbon-fiber: 2x2 alternating-orientation weave with sin² fiber highlights (sci-fi/tech panels)\n");
     std::printf("  --add-texture-to-zone <zoneDir> <png-path> [renameTo]\n");
     std::printf("                         Copy an existing PNG into <zoneDir> (optionally renaming it on the way in)\n");
     std::printf("  --gen-mesh <wom-base> <cube|plane|sphere|cylinder|torus|cone|ramp> [size]\n");