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fix: preserve MXCSR around earcut triangulation to support UE5 builds… #1386

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fix: preserve MXCSR around earcut triangulation to support UE5 builds… #1386

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23 changes: 22 additions & 1 deletion CesiumGeospatial/src/CartographicPolygon.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -16,6 +16,13 @@
#include <utility>
#include <vector>


#if defined(_MSC_VER)
#include <intrin.h>
#elif defined(__x86_64__) || defined(__i386__)
#include <x86intrin.h>
#endif

using namespace CesiumGeometry;

namespace CesiumGeospatial {
Expand Down Expand Up @@ -57,7 +64,21 @@ triangulatePolygon(const std::vector<glm::dvec2>& polygon) {

localPolygons.emplace_back(std::move(localPolygon));

// Save the current MXCSR state and disable DAZ (bit 6) and FTZ (bit 15)
// before calling mapbox::earcut. These flags, enabled by UE5 in packaged
// builds, cause earcut's floating-point predicates to produce incorrect
// triangulation results by flushing denormal values to zero.
#if defined(__x86_64__) || defined(_M_X64) || defined(__i386__) || defined(_M_IX86)
unsigned int _oldMxcsr = _mm_getcsr();
_mm_setcsr(_oldMxcsr & ~((1u << 6) | (1u << 15)));
#endif

indices = mapbox::earcut<uint32_t>(localPolygons);

#if defined(__x86_64__) || defined(_M_X64) || defined(__i386__) || defined(_M_IX86)
_mm_setcsr(_oldMxcsr);
#endif

return indices;
}

Expand Down Expand Up @@ -296,4 +317,4 @@ CartographicPolygon::CartographicPolygon(const std::vector<glm::dvec2>& polygon)
return true;
}

} // namespace CesiumGeospatial
} // namespace CesiumGeospatial