fix(IBA): keep nearest resample off the Highway path

src/libOpenImageIO/imagebufalgo_hwy_pvt.h

@@ -1100,7 +1100,7 @@ hwy_binary_perpixel_op_rgba_rgb_roi(ImageBuf& R, const ImageBuf& A,
                 (void)ba;
 
                 using DstLaneT = HwyLaneTypeT<Rtype>;
-                auto d_dstlane = hn::Rebind<DstLaneT, decltype(d)>();
+                auto d_dstlane = hn::Rebind<DstLaneT, hn::ScalableTag<MathT>>();
                 hn::Vec<decltype(d_dstlane)> dr, dg, db, da;
                 hn::LoadInterleaved4(d_dstlane,
                                      reinterpret_cast<const DstLaneT*>(r_row
@@ -1189,7 +1189,7 @@ hwy_ternary_perpixel_op_rgba_rgb_roi(ImageBuf& R, const ImageBuf& A,
                 (void)ca;
 
                 using DstLaneT = HwyLaneTypeT<Rtype>;
-                auto d_dstlane = hn::Rebind<DstLaneT, decltype(d)>();
+                auto d_dstlane = hn::Rebind<DstLaneT, hn::ScalableTag<MathT>>();
                 hn::Vec<decltype(d_dstlane)> dr, dg, db, da;
                 hn::LoadInterleaved4(d_dstlane,
                                      reinterpret_cast<const DstLaneT*>(r_row

src/libOpenImageIO/imagebufalgo_test.cpp

@@ -739,6 +739,40 @@ test_zover()
 
 
 // Test ImageBuf::resample
+// resample_hwy() ignores its `interpolate` argument and always bilerps, so
+// nearest sampling has to stay off that path. Highway is off by default, so a
+// reference image would not exercise this; compare the two settings instead.
+void
+test_resample_hwy_nearest()
+{
+    std::cout << "test resample nearest is not routed to Highway\n";
+
+    int prev_hwy = 0;
+    OIIO::getattribute("enable_hwy", prev_hwy);
+
+    // Neighbouring pixels must differ, or bilerp and nearest would agree and
+    // the test would pass on broken code.
+    ImageSpec srcspec(64, 48, 4, TypeFloat);
+    ImageBuf src(srcspec);
+    for (ImageBuf::Iterator<float> it(src); !it.done(); ++it)
+        for (int c = 0; c < 4; ++c)
+            it[c] = float(((it.x() + it.y() + c) % 7) * 0.125f);
+
+    ImageSpec dstspec(37, 29, 4, TypeFloat);
+    ImageBuf without_hwy(dstspec), with_hwy(dstspec);
+    OIIO::attribute("enable_hwy", 0);
+    OIIO_CHECK_ASSERT(ImageBufAlgo::resample(without_hwy, src, false));
+    OIIO::attribute("enable_hwy", 1);
+    OIIO_CHECK_ASSERT(ImageBufAlgo::resample(with_hwy, src, false));
+    OIIO::attribute("enable_hwy", prev_hwy);
+
+    OIIO_CHECK_EQUAL(memcmp(with_hwy.localpixels(), without_hwy.localpixels(),
+                            dstspec.image_bytes()),
+                     0);
+}
+
+
+
 void
 test_resample()
 {
@@ -1811,6 +1845,7 @@ main(int argc, char** argv)
     test_over(TypeFloat);
     test_over(TypeHalf);
     test_zover();
+    test_resample_hwy_nearest();
     test_resample();
     test_compare();
     test_isConstantColor();

src/libOpenImageIO/imagebufalgo_xform.cpp

@@ -1272,6 +1272,9 @@ static bool
 resample_hwy(ImageBuf& dst, const ImageBuf& src, bool interpolate, ROI roi,
              int nthreads)
 {
+    // This routine has no nearest case -- it always interpolates -- so
+    // resample_() must not route nearest sampling here.
+    OIIO_ASSERT(interpolate);
     using SimdType
         = std::conditional_t<std::is_same_v<DSTTYPE, double>, double, float>;
     using D      = hn::ScalableTag<SimdType>;
@@ -1435,7 +1438,10 @@ resample_(ImageBuf& dst, const ImageBuf& src, bool interpolate, ROI roi,
           int nthreads)
 {
 #if OIIO_USE_HWY
-    if (OIIO::pvt::enable_hwy && HwySupports<DSTTYPE>(dst, roi)
+    // Interpolating only: resample_hwy() ignores its `interpolate` argument
+    // and always bilerps, so sending nearest here silently returns filtered
+    // pixels instead of the source pixel the caller asked for.
+    if (interpolate && OIIO::pvt::enable_hwy && HwySupports<DSTTYPE>(dst, roi)
         && HwySupports<SRCTYPE>(src, ROI()))
         return resample_hwy<DSTTYPE, SRCTYPE>(dst, src, interpolate, roi,
                                               nthreads);