[Bf-blender-cvs] [21bc1a99baa] master: Cycles: optimize ensure_valid_reflection(), reduces render time by about 1%
Mikhail
noreply at git.blender.org
Mon Mar 15 18:15:48 CET 2021
Commit: 21bc1a99baa765d81c3203fd2e451681b8a7fd55
Author: Mikhail
Date: Mon Mar 15 17:59:38 2021 +0100
Branches: master
https://developer.blender.org/rB21bc1a99baa765d81c3203fd2e451681b8a7fd55
Cycles: optimize ensure_valid_reflection(), reduces render time by about 1%
This is an implementation that is about 1.5-2.1 times faster. It gives a result
that is on average 6° different from the old implementation. The difference is
because normals (Ng, N, N') are not selected to be coplanar, but instead
reflection R is lifted the least amount and the N' is computed as a bisector.
Differential Revision: https://developer.blender.org/D10084
===================================================================
M intern/cycles/kernel/kernel_montecarlo.h
M intern/cycles/kernel/shaders/stdcycles.h
===================================================================
diff --git a/intern/cycles/kernel/kernel_montecarlo.h b/intern/cycles/kernel/kernel_montecarlo.h
index ce37bd0b15e..ba25c0e24e4 100644
--- a/intern/cycles/kernel/kernel_montecarlo.h
+++ b/intern/cycles/kernel/kernel_montecarlo.h
@@ -195,108 +195,31 @@ ccl_device float2 regular_polygon_sample(float corners, float rotation, float u,
ccl_device float3 ensure_valid_reflection(float3 Ng, float3 I, float3 N)
{
- float3 R = 2 * dot(N, I) * N - I;
-
- /* Reflection rays may always be at least as shallow as the incoming ray. */
- float threshold = min(0.9f * dot(Ng, I), 0.01f);
- if (dot(Ng, R) >= threshold) {
- return N;
- }
-
- /* Form coordinate system with Ng as the Z axis and N inside the X-Z-plane.
- * The X axis is found by normalizing the component of N that's orthogonal to Ng.
- * The Y axis isn't actually needed.
- */
- float NdotNg = dot(N, Ng);
- float3 X = normalize(N - NdotNg * Ng);
-
- /* Keep math expressions. */
- /* clang-format off */
- /* Calculate N.z and N.x in the local coordinate system.
- *
- * The goal of this computation is to find a N' that is rotated towards Ng just enough
- * to lift R' above the threshold (here called t), therefore dot(R', Ng) = t.
- *
- * According to the standard reflection equation,
- * this means that we want dot(2*dot(N', I)*N' - I, Ng) = t.
- *
- * Since the Z axis of our local coordinate system is Ng, dot(x, Ng) is just x.z, so we get
- * 2*dot(N', I)*N'.z - I.z = t.
- *
- * The rotation is simple to express in the coordinate system we formed -
- * since N lies in the X-Z-plane, we know that N' will also lie in the X-Z-plane,
- * so N'.y = 0 and therefore dot(N', I) = N'.x*I.x + N'.z*I.z .
- *
- * Furthermore, we want N' to be normalized, so N'.x = sqrt(1 - N'.z^2).
- *
- * With these simplifications,
- * we get the final equation 2*(sqrt(1 - N'.z^2)*I.x + N'.z*I.z)*N'.z - I.z = t.
- *
- * The only unknown here is N'.z, so we can solve for that.
- *
- * The equation has four solutions in general:
- *
- * N'.z = +-sqrt(0.5*(+-sqrt(I.x^2*(I.x^2 + I.z^2 - t^2)) + t*I.z + I.x^2 + I.z^2)/(I.x^2 + I.z^2))
- * We can simplify this expression a bit by grouping terms:
- *
- * a = I.x^2 + I.z^2
- * b = sqrt(I.x^2 * (a - t^2))
- * c = I.z*t + a
- * N'.z = +-sqrt(0.5*(+-b + c)/a)
- *
- * Two solutions can immediately be discarded because they're negative so N' would lie in the
- * lower hemisphere.
- */
- /* clang-format on */
-
- float Ix = dot(I, X), Iz = dot(I, Ng);
- float Ix2 = sqr(Ix), Iz2 = sqr(Iz);
- float a = Ix2 + Iz2;
-
- float b = safe_sqrtf(Ix2 * (a - sqr(threshold)));
- float c = Iz * threshold + a;
-
- /* Evaluate both solutions.
- * In many cases one can be immediately discarded (if N'.z would be imaginary or larger than
- * one), so check for that first. If no option is viable (might happen in extreme cases like N
- * being in the wrong hemisphere), give up and return Ng. */
- float fac = 0.5f / a;
- float N1_z2 = fac * (b + c), N2_z2 = fac * (-b + c);
- bool valid1 = (N1_z2 > 1e-5f) && (N1_z2 <= (1.0f + 1e-5f));
- bool valid2 = (N2_z2 > 1e-5f) && (N2_z2 <= (1.0f + 1e-5f));
-
- float2 N_new;
- if (valid1 && valid2) {
- /* If both are possible, do the expensive reflection-based check. */
- float2 N1 = make_float2(safe_sqrtf(1.0f - N1_z2), safe_sqrtf(N1_z2));
- float2 N2 = make_float2(safe_sqrtf(1.0f - N2_z2), safe_sqrtf(N2_z2));
-
- float R1 = 2 * (N1.x * Ix + N1.y * Iz) * N1.y - Iz;
- float R2 = 2 * (N2.x * Ix + N2.y * Iz) * N2.y - Iz;
-
- valid1 = (R1 >= 1e-5f);
- valid2 = (R2 >= 1e-5f);
- if (valid1 && valid2) {
- /* If both solutions are valid, return the one with the shallower reflection since it will be
- * closer to the input (if the original reflection wasn't shallow, we would not be in this
- * part of the function). */
- N_new = (R1 < R2) ? N1 : N2;
+ float3 R;
+ float NI = dot(N, I);
+ float NgR, threshold;
+
+ /* Check if the incident ray is coming from behind normal N. */
+ if (NI > 0) {
+ /* Normal reflection */
+ R = (2 * NI) * N - I;
+ NgR = dot(Ng, R);
+
+ /* Reflection rays may always be at least as shallow as the incoming ray. */
+ threshold = min(0.9f * dot(Ng, I), 0.01f);
+ if (NgR >= threshold) {
+ return N;
}
- else {
- /* If only one reflection is valid (= positive), pick that one. */
- N_new = (R1 > R2) ? N1 : N2;
- }
- }
- else if (valid1 || valid2) {
- /* Only one solution passes the N'.z criterium, so pick that one. */
- float Nz2 = valid1 ? N1_z2 : N2_z2;
- N_new = make_float2(safe_sqrtf(1.0f - Nz2), safe_sqrtf(Nz2));
}
else {
- return Ng;
+ /* Bad incident */
+ R = -I;
+ NgR = dot(Ng, R);
+ threshold = 0.01f;
}
- return N_new.x * X + N_new.y * Ng;
+ R = R + Ng * (threshold - NgR); /* Lift the reflection above the threshold. */
+ return normalize(I * len(R) + R * len(I)); /* Find a bisector. */
}
CCL_NAMESPACE_END
diff --git a/intern/cycles/kernel/shaders/stdcycles.h b/intern/cycles/kernel/shaders/stdcycles.h
index dd604da68ce..af7b645d9a2 100644
--- a/intern/cycles/kernel/shaders/stdcycles.h
+++ b/intern/cycles/kernel/shaders/stdcycles.h
@@ -84,67 +84,30 @@ closure color principled_hair(normal N,
closure color henyey_greenstein(float g) BUILTIN;
closure color absorption() BUILTIN;
-normal ensure_valid_reflection(normal Ng, vector I, normal N)
+normal ensure_valid_reflection(normal Ng, normal I, normal N)
{
/* The implementation here mirrors the one in kernel_montecarlo.h,
* check there for an explanation of the algorithm. */
-
- float sqr(float x)
- {
- return x * x;
- }
-
- vector R = 2 * dot(N, I) * N - I;
-
- float threshold = min(0.9 * dot(Ng, I), 0.01);
- if (dot(Ng, R) >= threshold) {
- return N;
- }
-
- float NdotNg = dot(N, Ng);
- vector X = normalize(N - NdotNg * Ng);
-
- float Ix = dot(I, X), Iz = dot(I, Ng);
- float Ix2 = sqr(Ix), Iz2 = sqr(Iz);
- float a = Ix2 + Iz2;
-
- float b = sqrt(Ix2 * (a - sqr(threshold)));
- float c = Iz * threshold + a;
-
- float fac = 0.5 / a;
- float N1_z2 = fac * (b + c), N2_z2 = fac * (-b + c);
- int valid1 = (N1_z2 > 1e-5) && (N1_z2 <= (1.0 + 1e-5));
- int valid2 = (N2_z2 > 1e-5) && (N2_z2 <= (1.0 + 1e-5));
-
- float N_new_x, N_new_z;
- if (valid1 && valid2) {
- float N1_x = sqrt(1.0 - N1_z2), N1_z = sqrt(N1_z2);
- float N2_x = sqrt(1.0 - N2_z2), N2_z = sqrt(N2_z2);
-
- float R1 = 2 * (N1_x * Ix + N1_z * Iz) * N1_z - Iz;
- float R2 = 2 * (N2_x * Ix + N2_z * Iz) * N2_z - Iz;
-
- valid1 = (R1 >= 1e-5);
- valid2 = (R2 >= 1e-5);
- if (valid1 && valid2) {
- N_new_x = (R1 < R2) ? N1_x : N2_x;
- N_new_z = (R1 < R2) ? N1_z : N2_z;
- }
- else {
- N_new_x = (R1 > R2) ? N1_x : N2_x;
- N_new_z = (R1 > R2) ? N1_z : N2_z;
+ vector R;
+ float NI = dot(N, I);
+ float NgR, threshold;
+
+ if (NI > 0) {
+ R = (2 * NI) * N - I;
+ NgR = dot(Ng, R);
+ threshold = min(0.9 * dot(Ng, I), 0.01);
+ if (NgR >= threshold) {
+ return N;
}
}
- else if (valid1 || valid2) {
- float Nz2 = valid1 ? N1_z2 : N2_z2;
- N_new_x = sqrt(1.0 - Nz2);
- N_new_z = sqrt(Nz2);
- }
else {
- return Ng;
+ R = -I;
+ NgR = dot(Ng, R);
+ threshold = 0.01;
}
- return N_new_x * X + N_new_z * Ng;
+ R = R + Ng * (threshold - NgR);
+ return normalize(I * length(R) + R * length(I));
}
#endif /* CCL_STDOSL_H */
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