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Cycles: initial subsurface multiple scattering support. It's not working as

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well as I would like, but it works, just add a subsurface scattering node and
you can use it like any other BSDF.

It is using fully raytraced sampling compatible with progressive rendering
and other more advanced rendering algorithms we might used in the future, and
it uses no extra memory so it's suitable for complex scenes.

Disadvantage is that it can be quite noisy and slow. Two limitations that will
be solved are that it does not work with bump mapping yet, and that the falloff
function used is a simple cubic function, it's not using the real BSSRDF
falloff function yet.

The node has a color input, along with a scattering radius for each RGB color
channel along with an overall scale factor for the radii.

There is also no GPU support yet, will test if I can get that working later.

Node Documentation:
http://wiki.blender.org/index.php/Doc:2.6/Manual/Render/Cycles/Nodes/Shaders#BSSRDF

Implementation notes:
http://wiki.blender.org/index.php/Dev:2.6/Source/Render/Cycles/Subsurface_Scattering
This commit is contained in:
Brecht Van Lommel
2013-04-01 20:26:52 +00:00
parent 40b05d364e
commit de9dffc61e
55 changed files with 1806 additions and 254 deletions
Download Patch File Download Diff File Expand all files Collapse all files

320
intern/cycles/kernel/kernel_bvh.h
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@@ -923,6 +923,322 @@ __device_inline bool scene_intersect(KernelGlobals *kg, const Ray *ray, const ui
#endif
}
/* Special ray intersection routines for subsurface scattering. In that case we
* only want to intersect with primitives in the same object, and if case of
* multiple hits we pick a single random primitive as the intersection point. */
__device_inline void bvh_triangle_intersect_subsurface(KernelGlobals *kg, Intersection *isect,
float3 P, float3 idir, int object, int triAddr, float tmax, int *num_hits, float subsurface_random)
{
/* compute and check intersection t-value */
float4 v00 = kernel_tex_fetch(__tri_woop, triAddr*TRI_NODE_SIZE+0);
float4 v11 = kernel_tex_fetch(__tri_woop, triAddr*TRI_NODE_SIZE+1);
float3 dir = 1.0f/idir;
float Oz = v00.w - P.x*v00.x - P.y*v00.y - P.z*v00.z;
float invDz = 1.0f/(dir.x*v00.x + dir.y*v00.y + dir.z*v00.z);
float t = Oz * invDz;
if(t > 0.0f && t < tmax) {
/* compute and check barycentric u */
float Ox = v11.w + P.x*v11.x + P.y*v11.y + P.z*v11.z;
float Dx = dir.x*v11.x + dir.y*v11.y + dir.z*v11.z;
float u = Ox + t*Dx;
if(u >= 0.0f) {
/* compute and check barycentric v */
float4 v22 = kernel_tex_fetch(__tri_woop, triAddr*TRI_NODE_SIZE+2);
float Oy = v22.w + P.x*v22.x + P.y*v22.y + P.z*v22.z;
float Dy = dir.x*v22.x + dir.y*v22.y + dir.z*v22.z;
float v = Oy + t*Dy;
if(v >= 0.0f && u + v <= 1.0f) {
(*num_hits)++;
if(subsurface_random * (*num_hits) <= 1.0f) {
/* record intersection */
isect->prim = triAddr;
isect->object = object;
isect->u = u;
isect->v = v;
isect->t = t;
}
}
}
}
}
__device_inline int bvh_intersect_subsurface(KernelGlobals *kg, const Ray *ray, Intersection *isect, int subsurface_object, float subsurface_random)
{
/* traversal stack in CUDA thread-local memory */
int traversalStack[BVH_STACK_SIZE];
traversalStack[0] = ENTRYPOINT_SENTINEL;
/* traversal variables in registers */
int stackPtr = 0;
int nodeAddr = kernel_data.bvh.root;
/* ray parameters in registers */
const float tmax = ray->t;
float3 P = ray->P;
float3 idir = bvh_inverse_direction(ray->D);
int object = ~0;
int num_hits = 0;
isect->t = tmax;
isect->object = ~0;
isect->prim = ~0;
isect->u = 0.0f;
isect->v = 0.0f;
/* traversal loop */
do {
do
{
/* traverse internal nodes */
while(nodeAddr >= 0 && nodeAddr != ENTRYPOINT_SENTINEL)
{
bool traverseChild0, traverseChild1, closestChild1;
int nodeAddrChild1;
bvh_node_intersect(kg, &traverseChild0, &traverseChild1,
&closestChild1, &nodeAddr, &nodeAddrChild1,
P, idir, isect->t, ~0, nodeAddr);
if(traverseChild0 != traverseChild1) {
/* one child was intersected */
if(traverseChild1) {
nodeAddr = nodeAddrChild1;
}
}
else {
if(!traverseChild0) {
/* neither child was intersected */
nodeAddr = traversalStack[stackPtr];
--stackPtr;
}
else {
/* both children were intersected, push the farther one */
if(closestChild1) {
int tmp = nodeAddr;
nodeAddr = nodeAddrChild1;
nodeAddrChild1 = tmp;
}
++stackPtr;
traversalStack[stackPtr] = nodeAddrChild1;
}
}
}
/* if node is leaf, fetch triangle list */
if(nodeAddr < 0) {
float4 leaf = kernel_tex_fetch(__bvh_nodes, (-nodeAddr-1)*BVH_NODE_SIZE+(BVH_NODE_SIZE-1));
int primAddr = __float_as_int(leaf.x);
#ifdef __INSTANCING__
if(primAddr >= 0) {
#endif
int primAddr2 = __float_as_int(leaf.y);
/* pop */
nodeAddr = traversalStack[stackPtr];
--stackPtr;
/* primitive intersection */
while(primAddr < primAddr2) {
/* only primitives from the same object */
uint tri_object = (object == ~0)? kernel_tex_fetch(__prim_object, primAddr): object;
if(tri_object == subsurface_object) {
/* intersect ray against primitive */
#ifdef __HAIR__
uint segment = kernel_tex_fetch(__prim_segment, primAddr);
if(segment == ~0) /* ignore hair for sss */
#endif
bvh_triangle_intersect_subsurface(kg, isect, P, idir, object, primAddr, tmax, &num_hits, subsurface_random);
}
primAddr++;
}
#ifdef __INSTANCING__
}
else {
/* instance push */
if(subsurface_object == kernel_tex_fetch(__prim_object, -primAddr-1)) {
object = subsurface_object;
bvh_instance_push(kg, object, ray, &P, &idir, &isect->t, tmax);
++stackPtr;
traversalStack[stackPtr] = ENTRYPOINT_SENTINEL;
nodeAddr = kernel_tex_fetch(__object_node, object);
}
}
#endif
}
} while(nodeAddr != ENTRYPOINT_SENTINEL);
#ifdef __INSTANCING__
if(stackPtr >= 0) {
kernel_assert(object != ~0);
/* instance pop */
bvh_instance_pop(kg, object, ray, &P, &idir, &isect->t, tmax);
object = ~0;
nodeAddr = traversalStack[stackPtr];
--stackPtr;
}
#endif
} while(nodeAddr != ENTRYPOINT_SENTINEL);
return num_hits;
}
#ifdef __OBJECT_MOTION__
__device bool bvh_intersect_motion_subsurface(KernelGlobals *kg, const Ray *ray, Intersection *isect, int subsurface_object, float subsurface_random)
{
/* traversal stack in CUDA thread-local memory */
int traversalStack[BVH_STACK_SIZE];
traversalStack[0] = ENTRYPOINT_SENTINEL;
/* traversal variables in registers */
int stackPtr = 0;
int nodeAddr = kernel_data.bvh.root;
/* ray parameters in registers */
const float tmax = ray->t;
float3 P = ray->P;
float3 idir = bvh_inverse_direction(ray->D);
int object = ~0;
int num_hits = 0;
Transform ob_tfm;
isect->t = tmax;
isect->object = ~0;
isect->prim = ~0;
isect->u = 0.0f;
isect->v = 0.0f;
/* traversal loop */
do {
do
{
/* traverse internal nodes */
while(nodeAddr >= 0 && nodeAddr != ENTRYPOINT_SENTINEL)
{
bool traverseChild0, traverseChild1, closestChild1;
int nodeAddrChild1;
bvh_node_intersect(kg, &traverseChild0, &traverseChild1,
&closestChild1, &nodeAddr, &nodeAddrChild1,
P, idir, isect->t, ~0, nodeAddr);
if(traverseChild0 != traverseChild1) {
/* one child was intersected */
if(traverseChild1) {
nodeAddr = nodeAddrChild1;
}
}
else {
if(!traverseChild0) {
/* neither child was intersected */
nodeAddr = traversalStack[stackPtr];
--stackPtr;
}
else {
/* both children were intersected, push the farther one */
if(closestChild1) {
int tmp = nodeAddr;
nodeAddr = nodeAddrChild1;
nodeAddrChild1 = tmp;
}
++stackPtr;
traversalStack[stackPtr] = nodeAddrChild1;
}
}
}
/* if node is leaf, fetch triangle list */
if(nodeAddr < 0) {
float4 leaf = kernel_tex_fetch(__bvh_nodes, (-nodeAddr-1)*BVH_NODE_SIZE+(BVH_NODE_SIZE-1));
int primAddr = __float_as_int(leaf.x);
if(primAddr >= 0) {
int primAddr2 = __float_as_int(leaf.y);
/* pop */
nodeAddr = traversalStack[stackPtr];
--stackPtr;
/* primitive intersection */
while(primAddr < primAddr2) {
/* only primitives from the same object */
uint tri_object = (object == ~0)? kernel_tex_fetch(__prim_object, primAddr): object;
if(tri_object == subsurface_object) {
/* intersect ray against primitive */
#ifdef __HAIR__
uint segment = kernel_tex_fetch(__prim_segment, primAddr);
if(segment == ~0) /* ignore hair for sss */
#endif
bvh_triangle_intersect_subsurface(kg, isect, P, idir, object, primAddr, tmax, &num_hits, subsurface_random);
}
primAddr++;
}
}
else {
/* instance push */
if(subsurface_object == kernel_tex_fetch(__prim_object, -primAddr-1)) {
object = subsurface_object;
object = kernel_tex_fetch(__prim_object, -primAddr-1);
bvh_instance_motion_push(kg, object, ray, &P, &idir, &isect->t, &ob_tfm, tmax);
++stackPtr;
traversalStack[stackPtr] = ENTRYPOINT_SENTINEL;
nodeAddr = kernel_tex_fetch(__object_node, object);
}
}
}
} while(nodeAddr != ENTRYPOINT_SENTINEL);
if(stackPtr >= 0) {
kernel_assert(object != ~0);
/* instance pop */
bvh_instance_motion_pop(kg, object, ray, &P, &idir, &isect->t, &ob_tfm, tmax);
object = ~0;
nodeAddr = traversalStack[stackPtr];
--stackPtr;
}
} while(nodeAddr != ENTRYPOINT_SENTINEL);
return num_hits;
}
#endif
__device_inline int scene_intersect_subsurface(KernelGlobals *kg, const Ray *ray, Intersection *isect, int subsurface_object, float subsurface_random)
{
#ifdef __OBJECT_MOTION__
if(kernel_data.bvh.have_motion)
return bvh_intersect_motion_subsurface(kg, ray, isect, subsurface_object, subsurface_random);
else
return bvh_intersect_subsurface(kg, ray, isect, subsurface_object, subsurface_random);
#else
return bvh_intersect_subsurface(kg, ray, isect, subsurface_object, subsurface_random);
#endif
}
/* Ray offset to avoid self intersection */
__device_inline float3 ray_offset(float3 P, float3 Ng)
{
#ifdef __INTERSECTION_REFINE__
@@ -971,6 +1287,10 @@ __device_inline float3 ray_offset(float3 P, float3 Ng)
#endif
}
/* Refine triangle intersection to more precise hit point. For rays that travel
* far the precision is often not so good, this reintersects the primitive from
* a closer distance. */
__device_inline float3 bvh_triangle_refine(KernelGlobals *kg, ShaderData *sd, const Intersection *isect, const Ray *ray)
{
float3 P = ray->P;