feat(procedural): add plasma, voronoi, normalmap generators

Add three new procedural texture generators:
- gen_plasma: classic sine-sum color texture (RGB output)
- gen_voronoi: Worley cellular noise (F1/F2/F2-F1 modes)
- gen_normalmap: post-process grayscale→RGB normal map

Remove gen_noise_256 (was an alias for gen_noise). Register new
generators in asset_manager and asset_packer. Add unit tests for
all three, and use them in test_3d_render (plasma sky, voronoi noise,
fBm normal map).

handoff(Gemini): plasma/voronoi/normalmap procedural generators added;
gen_noise_256 removed; tests + 3d_render usage wired up.

1 files changed, 88 insertions, 0 deletions

diff --git a/src/tests/util/test_procedural.cc b/src/tests/util/test_procedural.cc
index e9f9a02..c6616ad 100644
--- a/src/tests/util/test_procedural.cc
+++ b/src/tests/util/test_procedural.cc
@@ -127,11 +127,99 @@ void test_periodic() {
   assert(res); // Should return true but do nothing
 }
 
+void test_plasma() {
+  std::cout << "Testing Plasma Generator..." << std::endl;
+  int w = 64, h = 64;
+  std::vector<uint8_t> buffer(w * h * 4);
+
+  float params[] = {0.0f, 2.0f};
+  bool res = procedural::gen_plasma(buffer.data(), w, h, params, 2);
+  assert(res);
+  assert(buffer[3] == 255);
+
+  // RGB should differ (color output, not grayscale)
+  bool has_color = false;
+  for (size_t i = 0; i < buffer.size(); i += 4) {
+    if (buffer[i] != buffer[i + 1] || buffer[i + 1] != buffer[i + 2]) {
+      has_color = true;
+      break;
+    }
+  }
+  assert(has_color);
+
+  // Test defaults
+  res = procedural::gen_plasma(buffer.data(), w, h, nullptr, 0);
+  assert(res);
+}
+
+void test_voronoi() {
+  std::cout << "Testing Voronoi Generator..." << std::endl;
+  int w = 64, h = 64;
+  std::vector<uint8_t> buffer(w * h * 4);
+
+  // F1 mode
+  float params_f1[] = {4.0f, 0.0f, 0.0f};
+  bool res = procedural::gen_voronoi(buffer.data(), w, h, params_f1, 3);
+  assert(res);
+  assert(buffer[3] == 255);
+
+  bool nonzero = false;
+  for (size_t i = 0; i < buffer.size(); i += 4) {
+    if (buffer[i] > 0) { nonzero = true; break; }
+  }
+  assert(nonzero);
+
+  // F2-F1 (borders) mode
+  float params_border[] = {4.0f, 2.0f, 0.0f};
+  res = procedural::gen_voronoi(buffer.data(), w, h, params_border, 3);
+  assert(res);
+
+  // Test defaults
+  res = procedural::gen_voronoi(buffer.data(), w, h, nullptr, 0);
+  assert(res);
+}
+
+void test_normalmap() {
+  std::cout << "Testing Normal Map Generator..." << std::endl;
+  int w = 64, h = 64;
+  std::vector<uint8_t> buffer(w * h * 4);
+
+  // Fill with a horizontal gradient as height
+  for (int y = 0; y < h; ++y) {
+    for (int x = 0; x < w; ++x) {
+      int idx = (y * w + x) * 4;
+      buffer[idx] = (uint8_t)(x * 255 / (w - 1));
+      buffer[idx + 1] = buffer[idx];
+      buffer[idx + 2] = buffer[idx];
+      buffer[idx + 3] = 255;
+    }
+  }
+
+  float params[] = {4.0f};
+  bool res = procedural::gen_normalmap(buffer.data(), w, h, params, 1);
+  assert(res);
+  assert(buffer[3] == 255);
+
+  // For a horizontal gradient, X-normal (R) should be shifted from 128
+  // (non-flat normals expected)
+  bool has_normal_variation = false;
+  for (size_t i = 0; i < buffer.size(); i += 4) {
+    if (buffer[i] != 128) { has_normal_variation = true; break; }
+  }
+  assert(has_normal_variation);
+
+  // Z component (B) should be > 0 (normal faces up)
+  assert(buffer[2] > 0);
+}
+
 int main() {
   test_noise();
   test_perlin();
   test_grid();
   test_periodic();
+  test_plasma();
+  test_voronoi();
+  test_normalmap();
   std::cout << "--- PROCEDURAL TESTS PASSED ---" << std::endl;
   return 0;
 }
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