1 files changed, 101 insertions, 0 deletions
diff --git a/source/blender/geometry/intern/reverse_uv_sampler.cc b/source/blender/geometry/intern/reverse_uv_sampler.cc
new file mode 100644
index 00000000000..54df43db4ea
--- /dev/null
+++ b/source/blender/geometry/intern/reverse_uv_sampler.cc
@@ -0,0 +1,101 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+#include "GEO_reverse_uv_sampler.hh"
+
+#include "BLI_math_geom.h"
+#include "BLI_math_vector.hh"
+#include "BLI_task.hh"
+#include "BLI_timeit.hh"
+
+namespace blender::geometry {
+
+static int2 uv_to_cell_key(const float2 &uv, const int resolution)
+{
+  return int2{uv * resolution};
+}
+
+ReverseUVSampler::ReverseUVSampler(const Span<float2> uv_map, const Span<MLoopTri> looptris)
+    : uv_map_(uv_map), looptris_(looptris)
+{
+  resolution_ = std::max<int>(3, std::sqrt(looptris.size()) * 2);
+
+  for (const int looptri_index : looptris.index_range()) {
+    const MLoopTri &looptri = looptris[looptri_index];
+    const float2 &uv_0 = uv_map_[looptri.tri[0]];
+    const float2 &uv_1 = uv_map_[looptri.tri[1]];
+    const float2 &uv_2 = uv_map_[looptri.tri[2]];
+
+    const int2 key_0 = uv_to_cell_key(uv_0, resolution_);
+    const int2 key_1 = uv_to_cell_key(uv_1, resolution_);
+    const int2 key_2 = uv_to_cell_key(uv_2, resolution_);
+
+    const int2 min_key = math::min(math::min(key_0, key_1), key_2);
+    const int2 max_key = math::max(math::max(key_0, key_1), key_2);
+
+    for (int key_x = min_key.x; key_x <= max_key.x; key_x++) {
+      for (int key_y = min_key.y; key_y <= max_key.y; key_y++) {
+        const int2 key{key_x, key_y};
+        looptris_by_cell_.add(key, looptri_index);
+      }
+    }
+  }
+}
+
+ReverseUVSampler::Result ReverseUVSampler::sample(const float2 &query_uv) const
+{
+  const int2 cell_key = uv_to_cell_key(query_uv, resolution_);
+  const Span<int> looptri_indices = looptris_by_cell_.lookup(cell_key);
+
+  float best_dist = FLT_MAX;
+  float3 best_bary_weights;
+  const MLoopTri *best_looptri;
+
+  for (const int looptri_index : looptri_indices) {
+    const MLoopTri &looptri = looptris_[looptri_index];
+    const float2 &uv_0 = uv_map_[looptri.tri[0]];
+    const float2 &uv_1 = uv_map_[looptri.tri[1]];
+    const float2 &uv_2 = uv_map_[looptri.tri[2]];
+    float3 bary_weights;
+    if (!barycentric_coords_v2(uv_0, uv_1, uv_2, query_uv, bary_weights)) {
+      continue;
+    }
+
+    /* If #query_uv is in the triangle, the distance is <= 0. Otherwise, the larger the distance,
+     * the further away the uv is from the triangle. */
+    const float x_dist = std::max(-bary_weights.x, bary_weights.x - 1.0f);
+    const float y_dist = std::max(-bary_weights.y, bary_weights.y - 1.0f);
+    const float z_dist = std::max(-bary_weights.z, bary_weights.z - 1.0f);
+    const float dist = MAX3(x_dist, y_dist, z_dist);
+
+    if (dist <= 0.0f) {
+      /* Return early if the uv coordinate is in the triangle. */
+      return Result{ResultType::Ok, &looptri, bary_weights};
+    }
+
+    if (dist < best_dist) {
+      best_dist = dist;
+      best_bary_weights = bary_weights;
+      best_looptri = &looptri;
+    }
+  }
+
+  /* Allow for a small epsilon in case the uv is on th edge. */
+  if (best_dist < 0.00001f) {
+    return Result{ResultType::Ok, best_looptri, math::clamp(best_bary_weights, 0.0f, 1.0f)};
+  }
+
+  return Result{};
+}
+
+void ReverseUVSampler::sample_many(const Span<float2> query_uvs,
+                                   MutableSpan<Result> r_results) const
+{
+  BLI_assert(query_uvs.size() == r_results.size());
+  threading::parallel_for(query_uvs.index_range(), 256, [&](const IndexRange range) {
+    for (const int i : range) {
+      r_results[i] = this->sample(query_uvs[i]);
+    }
+  });
+}
+
+}  // namespace blender::geometry