Cycles microdisplacement: Improved automatic bump mapping

Object coordinates can now be used in the displacement shader and will give
correct results, where as before bump mapping was calculated from the displace
positions and resulted in incorrect shading.

This works by evaluating the shader in two parts, first bump then surface, and
setting the shader state to match what it would be if the surface was
undisplaced for the bump shader evaluation. Currently only `P` is set as if
undisplaced, but other shader variables could be set as well, such as `I` or
`time`. Since these aren't set to anything meaningful for displacement I left
them out of this patch, we can decide what to do with them separately.

Reviewed By: brecht

Differential Revision: https://developer.blender.org/D2156

3 files changed, 67 insertions, 1 deletions

diff --git a/intern/cycles/kernel/svm/svm.h b/intern/cycles/kernel/svm/svm.h
index 502994e71f1..998a32e3181 100644
--- a/intern/cycles/kernel/svm/svm.h
+++ b/intern/cycles/kernel/svm/svm.h
@@ -181,6 +181,7 @@ CCL_NAMESPACE_END
 #include "svm_brick.h"
 #include "svm_vector_transform.h"
 #include "svm_voxel.h"
+#include "svm_bump.h"
 
 CCL_NAMESPACE_BEGIN
 
@@ -294,6 +295,12 @@ ccl_device_noinline void svm_eval_nodes(KernelGlobals *kg, ShaderData *sd, ccl_a
 			case NODE_CLOSURE_SET_NORMAL:
 				svm_node_set_normal(kg, sd, stack, node.y, node.z);
 				break;
+			case NODE_ENTER_BUMP_EVAL:
+				svm_node_enter_bump_eval(kg, sd, stack, node.y);
+				break;
+			case NODE_LEAVE_BUMP_EVAL:
+				svm_node_leave_bump_eval(kg, sd, stack, node.y);
+				break;
 #    endif  /* NODES_FEATURE(NODE_FEATURE_BUMP) */
 			case NODE_HSV:
 				svm_node_hsv(kg, sd, stack, node, &offset);
diff --git a/intern/cycles/kernel/svm/svm_bump.h b/intern/cycles/kernel/svm/svm_bump.h
new file mode 100644
index 00000000000..04a8c7b64e5
--- /dev/null
+++ b/intern/cycles/kernel/svm/svm_bump.h
@@ -0,0 +1,54 @@
+/*
+ * Copyright 2011-2016 Blender Foundation
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+CCL_NAMESPACE_BEGIN
+
+/* Bump Eval Nodes */
+
+ccl_device void svm_node_enter_bump_eval(KernelGlobals *kg, ShaderData *sd, float *stack, uint offset)
+{
+	/* save state */
+	stack_store_float3(stack, offset+0, ccl_fetch(sd, P));
+	stack_store_float3(stack, offset+3, ccl_fetch(sd, dP).dx);
+	stack_store_float3(stack, offset+6, ccl_fetch(sd, dP).dy);
+
+	/* set state as if undisplaced */
+	const AttributeDescriptor desc = find_attribute(kg, sd, ATTR_STD_POSITION_UNDISPLACED);
+
+	if(desc.offset != ATTR_STD_NOT_FOUND) {
+		float3 P, dPdx, dPdy;
+		P = primitive_attribute_float3(kg, sd, desc, &dPdx, &dPdy);
+
+		object_position_transform(kg, sd, &P);
+		object_dir_transform(kg, sd, &dPdx);
+		object_dir_transform(kg, sd, &dPdy);
+
+		ccl_fetch(sd, P) = P;
+		ccl_fetch(sd, dP).dx = dPdx;
+		ccl_fetch(sd, dP).dy = dPdy;
+	}
+}
+
+ccl_device void svm_node_leave_bump_eval(KernelGlobals *kg, ShaderData *sd, float *stack, uint offset)
+{
+	/* restore state */
+	ccl_fetch(sd, P) = stack_load_float3(stack, offset+0);
+	ccl_fetch(sd, dP).dx = stack_load_float3(stack, offset+3);
+	ccl_fetch(sd, dP).dy = stack_load_float3(stack, offset+6);
+}
+
+CCL_NAMESPACE_END
+
diff --git a/intern/cycles/kernel/svm/svm_types.h b/intern/cycles/kernel/svm/svm_types.h
index 51083c31708..9cfa8395b85 100644
--- a/intern/cycles/kernel/svm/svm_types.h
+++ b/intern/cycles/kernel/svm/svm_types.h
@@ -26,6 +26,8 @@ CCL_NAMESPACE_BEGIN
 /* SVM stack offsets with this value indicate that it's not on the stack */
 #define SVM_STACK_INVALID 255 
 
+#define SVM_BUMP_EVAL_STATE_SIZE 9
+
 /* Nodes */
 
 /* Known frequencies of used nodes, used for selective nodes compilation
@@ -127,6 +129,8 @@ typedef enum ShaderNodeType {
 	NODE_HAIR_INFO,
 	NODE_UVMAP,
 	NODE_TEX_VOXEL,
+	NODE_ENTER_BUMP_EVAL,
+	NODE_LEAVE_BUMP_EVAL,
 } ShaderNodeType;
 
 typedef enum NodeAttributeType {
@@ -374,7 +378,8 @@ typedef enum NodeTexVoxelSpace {
 typedef enum ShaderType {
 	SHADER_TYPE_SURFACE,
 	SHADER_TYPE_VOLUME,
-	SHADER_TYPE_DISPLACEMENT
+	SHADER_TYPE_DISPLACEMENT,
+	SHADER_TYPE_BUMP,
 } ShaderType;
 
 /* Closure */