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Fixed ray differentials for analytical sphere #764

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Fixed ray differentials for analytical sphere #764

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52c2b66
fixed ray differentials for analytical sphere
mariasoroka Jun 2, 2023
1d5b005
fixed tests for analytical sphere
mariasoroka Jun 2, 2023
f848778
fixed uv coordinates for the sphere
mariasoroka Jun 2, 2023
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11 changes: 5 additions & 6 deletions src/shapes/sphere.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -525,12 +525,11 @@ class Sphere final : public Shape<Float, Spectrum> {

if (likely(need_uv)) {
Float rd_2 = dr::sqr(local.x()) + dr::sqr(local.y()),
theta = unit_angle_z(local),
phi = dr::atan2(local.y(), local.x());

dr::masked(phi, phi < 0.f) += 2.f * dr::Pi<Float>;

si.uv = Point2f(phi * dr::InvTwoPi<Float>, theta * dr::InvPi<Float>);
si.uv = Point2f(phi * dr::InvTwoPi<Float>, dr::fnmadd(0.5f, local.z(), 0.5f));
if (likely(need_dp_duv)) {
si.dp_du = Vector3f(-local.y(), local.x(), 0.f);

Expand All @@ -539,16 +538,16 @@ class Sphere final : public Shape<Float, Spectrum> {
cos_phi = local.x() * inv_rd,
sin_phi = local.y() * inv_rd;

si.dp_dv = Vector3f(local.z() * cos_phi,
local.z() * sin_phi,
-rd);
si.dp_dv = Vector3f(local.z() * cos_phi * inv_rd,
local.z() * sin_phi * inv_rd,
-1.f);

Mask singularity_mask = active && dr::eq(rd, 0.f);
if (unlikely(dr::any_or<true>(singularity_mask)))
si.dp_dv[singularity_mask] = Vector3f(1.f, 0.f, 0.f);

si.dp_du = to_world * si.dp_du * (2.f * dr::Pi<Float>);
si.dp_dv = to_world * si.dp_dv * dr::Pi<Float>;
si.dp_dv = to_world * si.dp_dv * 2.f;
}
}

Expand Down
14 changes: 7 additions & 7 deletions src/shapes/tests/test_sphere.py
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Original file line number Diff line number Diff line change
Expand Up @@ -74,17 +74,17 @@ def test03_ray_intersect_transform(variant_scalar_rgb):
si = s.ray_intersect(ray)
ray_u = mi.Ray3f(ray)
ray_v = mi.Ray3f(ray)
eps = 1e-4
eps = 1e-5
ray_u.o += si.dp_du * eps
ray_v.o += si.dp_dv * eps
si_u = s.ray_intersect(ray_u)
si_v = s.ray_intersect(ray_v)
if si_u.is_valid():
du = (si_u.uv - si.uv) / eps
assert dr.allclose(du, [1, 0], atol=2e-2)
assert dr.allclose(du, [1, 0], atol=6e-2)
if si_v.is_valid():
dv = (si_v.uv - si.uv) / eps
assert dr.allclose(dv, [0, 1], atol=2e-2)
assert dr.allclose(dv, [0, 1], atol=6e-2)


def test04_ray_intersect_vec(variant_scalar_rgb):
Expand Down Expand Up @@ -180,7 +180,7 @@ def test06_differentiable_surface_interaction_ray_forward(variants_all_ad_rgb):
si = shape.ray_intersect(ray)
si.uv *= 1.0
dr.forward(ray.o.z)
assert dr.allclose(dr.grad(si.uv), [0, -2 / (2.0 * dr.pi)])
assert dr.allclose(dr.grad(si.uv), [0, -1 / 2.0])

# # If the ray origin is shifted along the x-axis, so does si.n
dr.enable_grad(ray.o)
Expand Down Expand Up @@ -308,7 +308,7 @@ def test08_differentiable_surface_interaction_ray_forward_follow_shape(variants_

assert dr.allclose(dr.grad(si.p), 0.0)
assert dr.allclose(dr.grad(si.n), 0.0)
assert dr.allclose(dr.grad(si.uv), [0.0, -0.5])
assert dr.allclose(dr.grad(si.uv), [0.0, -0.25 * dr.pi])


def test09_si_singularity(variants_all_rgb):
Expand All @@ -318,7 +318,7 @@ def test09_si_singularity(variants_all_rgb):
si = scene.ray_intersect(ray)

assert dr.allclose(si.dp_du, [0, 0, 0])
assert dr.allclose(si.dp_dv, [dr.pi, 0, 0])
assert dr.allclose(si.dp_dv, [2, 0, 0])
assert dr.allclose(si.sh_frame.s, [1, 0, 0])
assert dr.allclose(si.sh_frame.t, [0, -1, 0])
assert dr.allclose(si.sh_frame.n, [0, 0, -1])
Expand All @@ -331,7 +331,7 @@ def test10_si_singularity_centered(variants_all_rgb):
si = scene.ray_intersect(ray)

assert dr.allclose(si.dp_du, [0, 0, 0])
assert dr.allclose(si.dp_dv, [dr.pi, 0, 0])
assert dr.allclose(si.dp_dv, [2, 0, 0])
assert dr.allclose(si.sh_frame.s, [1, 0, 0])
assert dr.allclose(si.sh_frame.t, [0, 1, 0])
assert dr.allclose(si.sh_frame.n, [0, 0, 1])