fix ImageBlock issues

This commit addresses an ImageBlock issue that occurred when ImageBlock
was used with the parameters coalesce=false, normalize=True, and when
the sample footprint reached beyond the boundary.

It also updates Dr.Jit-Core to fix a loop recording issue (size of side
effects not correctly propagated) that I found along the way.

src/render/imageblock.cpp

@@ -265,17 +265,25 @@ MI_VARIANT void ImageBlock<Float, Spectrum>::put(const Point2f &pos,
 
             // Evaluate filters weights along the X and Y axes
 
-            for (uint32_t i = 0; i < count.x(); ++i) {
-                new (weights_x + i)
-                    Float(JIT ? m_rfilter->eval(rel_f.x())
-                              : m_rfilter->eval_discretized(rel_f.x()));
+            for (uint32_t x = 0; x < count.x(); ++x) {
+                Float wx = JIT ? m_rfilter->eval(rel_f.x())
+                               : m_rfilter->eval_discretized(rel_f.x());
+
+                if (unlikely(m_normalize))
+                    dr::masked(wx, x >= count_u.x()) = 0.f;
+
+                new (weights_x + x) Float(wx);
                 rel_f.x() += 1.f;
             }
 
-            for (uint32_t i = 0; i < count.y(); ++i) {
-                new (weights_y + i)
-                    Float(JIT ? m_rfilter->eval(rel_f.y())
-                              : m_rfilter->eval_discretized(rel_f.y()));
+            for (uint32_t y = 0; y < count.y(); ++y) {
+                Float wy = JIT ? m_rfilter->eval(rel_f.y())
+                               : m_rfilter->eval_discretized(rel_f.y());
+
+                if (unlikely(m_normalize))
+                    dr::masked(wy, y >= count_u.y()) = 0.f;
+
+                new (weights_y + y) Float(wy);
                 rel_f.y() += 1.f;
             }
 

src/render/tests/test_imageblock.py

@@ -192,3 +192,21 @@ def test04_read(variants_all, filter_name, border, offset, normalize, enable_ad)
                     ref /= dr.sum(weight)
 
             assert dr.allclose(value, ref, atol=1e-5)
+
+
+@pytest.mark.parametrize("coalesce", [ False, True ])
+@pytest.mark.parametrize("normalize", [ False, True ])
+def test05_boundary_effects(variants_vec_rgb, coalesce, normalize):
+    # Check that everything works correctly even when the image block
+    # is smaller than the filter kernel
+    rfilter = mi.load_dict({'type':'gaussian'})
+    ib = mi.ImageBlock(
+        size=(1, 1),
+        offset=(0, 0),
+        channel_count=1,
+        rfilter=rfilter,
+        normalize=normalize,
+        coalesce=coalesce
+    )
+    ib.put(pos=(0.5, 0.5), values=(dr.ones(mi.Float, 100),))
+    assert dr.allclose(ib.tensor().array, 100, rtol=1e-2)