HaxeJolt

lib/haxejolt/JoltPhysics/Jolt/Shaders/HairSkinRoots.hlsl

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+// Jolt Physics Library (https://github.com/jrouwe/JoltPhysics)
+// SPDX-FileCopyrightText: 2026 Jorrit Rouwe
+// SPDX-License-Identifier: MIT
+
+#include "HairSkinRootsBindings.h"
+#include "HairCommon.h"
+
+JPH_SHADER_FUNCTION_BEGIN(void, main, cHairPerStrandBatch, 1, 1)
+	JPH_SHADER_PARAM_THREAD_ID(tid)
+JPH_SHADER_FUNCTION_END
+{
+	// Check if this is a valid strand
+	uint strand_idx = tid.x;
+	if (strand_idx >= cNumStrands)
+		return;
+
+	JPH_HairSkinPoint sp = gSkinPoints[strand_idx];
+
+	// Get the vertices of the attached triangle
+	uint tri_idx = sp.mTriangleIndex * 3;
+	float3 v0 = JPH_Mat44Mul3x3Vec3(cScalpToHead, gScalpVertices[gScalpTriangles[tri_idx + 0]]);
+	float3 v1 = JPH_Mat44Mul3x3Vec3(cScalpToHead, gScalpVertices[gScalpTriangles[tri_idx + 1]]);
+	float3 v2 = JPH_Mat44Mul3x3Vec3(cScalpToHead, gScalpVertices[gScalpTriangles[tri_idx + 2]]);
+
+	JPH_HairPosition root;
+
+	// Set the position of the root
+	root.mPosition = sp.mU * v0 + sp.mV * v1 + (1.0f - sp.mU - sp.mV) * v2 + cScalpToHead[3].xyz;
+
+	// Get tangent vector
+	float3 tangent = normalize(v1 - v0);
+
+	// Get normal of the triangle
+	float3 normal = normalize(cross(tangent, v2 - v0));
+
+	// Calculate basis for the triangle
+	float3 binormal = cross(tangent, normal);
+	JPH_Quat triangle_basis = JPH_QuatFromMat33(normal, binormal, tangent);
+
+	// Calculate the new Bishop frame of the root
+	root.mRotation = JPH_QuatMulQuat(triangle_basis, JPH_QuatDecompress(sp.mToBishop));
+
+	gPositions[strand_idx] = root;
+
+	// Calculate the transform that transforms the stored global pose to the space of the skinned root of the strand
+	JPH_HairGlobalPoseTransform transform;
+	transform.mRotation = JPH_QuatMulQuat(root.mRotation, JPH_QuatConjugate(JPH_QuatDecompress(gInitialBishops[strand_idx])));
+	transform.mPosition = root.mPosition - JPH_QuatMulVec3(transform.mRotation, gInitialPositions[strand_idx]);
+	gGlobalPoseTransforms[strand_idx] = transform;
+}