Cycles: refactor rays to have start and end distance, fix precision issues

For transparency, volume and light intersection rays, adjust these distances
rather than the ray start position. This way we increment the start distance
by the smallest possible float increment to avoid self intersections, and be
sure it works as the distance compared to be will be exactly the same as
before, due to the ray start position and direction remaining the same.

Fix T98764, T96537, hair ray tracing precision issues.

Differential Revision: https://developer.blender.org/D15455

1 files changed, 20 insertions, 10 deletions

diff --git a/intern/cycles/kernel/device/metal/kernel.metal b/intern/cycles/kernel/device/metal/kernel.metal
index 74b4b079a32..764c26dbe8f 100644
--- a/intern/cycles/kernel/device/metal/kernel.metal
+++ b/intern/cycles/kernel/device/metal/kernel.metal
@@ -410,6 +410,7 @@ void metalrt_intersection_curve(constant KernelParamsMetal &launch_params_metal,
                                 const float3 ray_origin,
                                 const float3 ray_direction,
                                 float time,
+                                const float ray_tmin,
                                 const float ray_tmax,
                                 thread BoundingBoxIntersectionResult &result)
 {
@@ -434,7 +435,7 @@ void metalrt_intersection_curve(constant KernelParamsMetal &launch_params_metal,
     isect.t *= len;
 
   MetalKernelContext context(launch_params_metal);
-  if (context.curve_intersect(NULL, &isect, P, dir, isect.t, object, prim, time, type)) {
+  if (context.curve_intersect(NULL, &isect, P, dir, ray_tmin, isect.t, object, prim, time, type)) {
     result = metalrt_visibility_test<BoundingBoxIntersectionResult, METALRT_HIT_BOUNDING_BOX>(
                   launch_params_metal, payload, object, prim, isect.u);
     if (result.accept) {
@@ -456,6 +457,7 @@ void metalrt_intersection_curve_shadow(constant KernelParamsMetal &launch_params
                                        const float3 ray_origin,
                                        const float3 ray_direction,
                                        float time,
+                                       const float ray_tmin,
                                        const float ray_tmax,
                                        thread BoundingBoxIntersectionResult &result)
 {
@@ -475,7 +477,7 @@ void metalrt_intersection_curve_shadow(constant KernelParamsMetal &launch_params
     isect.t *= len;
 
   MetalKernelContext context(launch_params_metal);
-  if (context.curve_intersect(NULL, &isect, P, dir, isect.t, object, prim, time, type)) {
+  if (context.curve_intersect(NULL, &isect, P, dir, ray_tmin, isect.t, object, prim, time, type)) {
     result.continue_search = metalrt_shadow_all_hit<METALRT_HIT_BOUNDING_BOX>(
                 launch_params_metal, payload, object, prim, float2(isect.u, isect.v), ray_tmax);
     result.accept = !result.continue_search;
@@ -494,6 +496,7 @@ __intersection__curve_ribbon(constant KernelParamsMetal &launch_params_metal [[b
                              const uint primitive_id [[primitive_id]],
                              const float3 ray_origin [[origin]],
                              const float3 ray_direction [[direction]],
+                             const float ray_tmin [[min_distance]],
                              const float ray_tmax [[max_distance]])
 {
   uint prim = primitive_id + kernel_data_fetch(object_prim_offset, object);
@@ -511,7 +514,7 @@ __intersection__curve_ribbon(constant KernelParamsMetal &launch_params_metal [[b
 #  else
                                0.0f,
 #  endif
-                               ray_tmax, result);
+                               ray_tmin, ray_tmax, result);
   }
 
   return result;
@@ -525,6 +528,7 @@ __intersection__curve_ribbon_shadow(constant KernelParamsMetal &launch_params_me
                                     const uint primitive_id [[primitive_id]],
                                     const float3 ray_origin [[origin]],
                                     const float3 ray_direction [[direction]],
+                                    const float ray_tmin [[min_distance]],
                                     const float ray_tmax [[max_distance]])
 {
   uint prim = primitive_id + kernel_data_fetch(object_prim_offset, object);
@@ -542,7 +546,7 @@ __intersection__curve_ribbon_shadow(constant KernelParamsMetal &launch_params_me
 #  else
                                0.0f,
 #  endif
-                               ray_tmax, result);
+                               ray_tmin, ray_tmax, result);
   }
 
   return result;
@@ -556,6 +560,7 @@ __intersection__curve_all(constant KernelParamsMetal &launch_params_metal [[buff
                           const uint primitive_id [[primitive_id]],
                           const float3 ray_origin [[origin]],
                           const float3 ray_direction [[direction]],
+                          const float ray_tmin [[min_distance]],
                           const float ray_tmax [[max_distance]])
 {
   uint prim = primitive_id + kernel_data_fetch(object_prim_offset, object);
@@ -571,7 +576,7 @@ __intersection__curve_all(constant KernelParamsMetal &launch_params_metal [[buff
 #  else
                              0.0f,
 #  endif
-                             ray_tmax, result);
+                             ray_tmin, ray_tmax, result);
 
   return result;
 }
@@ -584,6 +589,7 @@ __intersection__curve_all_shadow(constant KernelParamsMetal &launch_params_metal
                                  const uint primitive_id [[primitive_id]],
                                  const float3 ray_origin [[origin]],
                                  const float3 ray_direction [[direction]],
+                                 const float ray_tmin [[min_distance]],
                                  const float ray_tmax [[max_distance]])
 {
   uint prim = primitive_id + kernel_data_fetch(object_prim_offset, object);
@@ -600,7 +606,7 @@ __intersection__curve_all_shadow(constant KernelParamsMetal &launch_params_metal
 #  else
                              0.0f,
 #  endif
-                             ray_tmax, result);
+                             ray_tmin, ray_tmax, result);
 
   return result;
 }
@@ -616,6 +622,7 @@ void metalrt_intersection_point(constant KernelParamsMetal &launch_params_metal,
                                 const float3 ray_origin,
                                 const float3 ray_direction,
                                 float time,
+                                const float ray_tmin,
                                 const float ray_tmax,
                                 thread BoundingBoxIntersectionResult &result)
 {
@@ -640,7 +647,7 @@ void metalrt_intersection_point(constant KernelParamsMetal &launch_params_metal,
     isect.t *= len;
 
   MetalKernelContext context(launch_params_metal);
-  if (context.point_intersect(NULL, &isect, P, dir, isect.t, object, prim, time, type)) {
+  if (context.point_intersect(NULL, &isect, P, dir, ray_tmin, isect.t, object, prim, time, type)) {
     result = metalrt_visibility_test<BoundingBoxIntersectionResult, METALRT_HIT_BOUNDING_BOX>(
                   launch_params_metal, payload, object, prim, isect.u);
     if (result.accept) {
@@ -662,6 +669,7 @@ void metalrt_intersection_point_shadow(constant KernelParamsMetal &launch_params
                                        const float3 ray_origin,
                                        const float3 ray_direction,
                                        float time,
+                                       const float ray_tmin,
                                        const float ray_tmax,
                                        thread BoundingBoxIntersectionResult &result)
 {
@@ -681,7 +689,7 @@ void metalrt_intersection_point_shadow(constant KernelParamsMetal &launch_params
     isect.t *= len;
 
   MetalKernelContext context(launch_params_metal);
-  if (context.point_intersect(NULL, &isect, P, dir, isect.t, object, prim, time, type)) {
+  if (context.point_intersect(NULL, &isect, P, dir, ray_tmin, isect.t, object, prim, time, type)) {
     result.continue_search = metalrt_shadow_all_hit<METALRT_HIT_BOUNDING_BOX>(
                 launch_params_metal, payload, object, prim, float2(isect.u, isect.v), ray_tmax);
     result.accept = !result.continue_search;
@@ -700,6 +708,7 @@ __intersection__point(constant KernelParamsMetal &launch_params_metal [[buffer(1
                              const uint primitive_id [[primitive_id]],
                              const float3 ray_origin [[origin]],
                              const float3 ray_direction [[direction]],
+                             const float ray_tmin [[min_distance]],
                              const float ray_tmax [[max_distance]])
 {
   const uint prim = primitive_id + kernel_data_fetch(object_prim_offset, object);
@@ -716,7 +725,7 @@ __intersection__point(constant KernelParamsMetal &launch_params_metal [[buffer(1
 #  else
                              0.0f,
 #  endif
-                             ray_tmax, result);
+                             ray_tmin, ray_tmax, result);
 
   return result;
 }
@@ -729,6 +738,7 @@ __intersection__point_shadow(constant KernelParamsMetal &launch_params_metal [[b
                                     const uint primitive_id [[primitive_id]],
                                     const float3 ray_origin [[origin]],
                                     const float3 ray_direction [[direction]],
+                                    const float ray_tmin [[min_distance]],
                                     const float ray_tmax [[max_distance]])
 {
   const uint prim = primitive_id + kernel_data_fetch(object_prim_offset, object);
@@ -745,7 +755,7 @@ __intersection__point_shadow(constant KernelParamsMetal &launch_params_metal [[b
 #  else
                              0.0f,
 #  endif
-                             ray_tmax, result);
+                             ray_tmin, ray_tmax, result);
 
   return result;
 }