+namespace {
+
+/// the "usual" type of gravity
+/// direction is towards the block's center, strength is inverse
+/// proportional to distance squared
+/// note that the effect can get clipped at distances > 16 units
+struct RadialGravity
+: public BlockGravity {
+
+ explicit RadialGravity(float strength)
+ : strength(strength) { }
+
+ glm::vec3 GetGravity(const glm::vec3 &diff, const glm::mat4 &) const noexcept override {
+ float dist2 = length2(diff);
+ glm::vec3 dir = -normalize(diff);
+ return dir * (strength / dist2);
+ }
+
+ float strength;
+
+};
+
+/// a "force field" variant of artificial gravity
+/// strength and direction is constant throughout the cuboid
+/// extent shouldn't exceed 16 units as gravity is only calculated for
+/// chunks surrounding and entity (and sometimes not even those if they're
+/// unavailable, but they will be for players)
+struct CuboidFieldGravity
+: public BlockGravity {
+
+ explicit CuboidFieldGravity(const glm::vec3 &strength, const AABB &extent)
+ : strength(strength), extent(extent) { }
+
+ glm::vec3 GetGravity(const glm::vec3 &diff, const glm::mat4 &M) const noexcept override {
+ /// rotate AABB endpoints accordingly, ignore translation
+ glm::vec3 min(M * glm::vec4(extent.min, 0.0f));
+ glm::vec3 max(M * glm::vec4(extent.max, 0.0f));
+ if (diff.x < min.x || diff.y < min.y || diff.z < min.z ||
+ diff.x > max.x || diff.y > max.y || diff.z > max.z) {
+ /// if point is outside, force is zero
+ return glm::vec3(0.0f);
+ } else {
+ /// otherwise it's out constant strength in block orientation
+ return glm::vec3(M * glm::vec4(strength, 0.0f));
+ }
+ }
+
+ glm::vec3 strength;
+ AABB extent;
+
+};
+
+
+}
+
+BlockGravity::~BlockGravity() {
+
+}
+
+std::unique_ptr<BlockGravity> BlockGravity::Read(TokenStreamReader &in) {
+ std::string type;
+ in.ReadIdentifier(type);
+ if (type == "Radial") {
+ float strength;
+ in.Skip(Token::PARENTHESIS_OPEN);
+ in.ReadNumber(strength);
+ in.Skip(Token::PARENTHESIS_CLOSE);
+ return std::unique_ptr<BlockGravity>(new RadialGravity(strength));
+ } else if (type == "CuboidField") {
+ glm::vec3 strength;
+ AABB extent;
+ in.Skip(Token::PARENTHESIS_OPEN);
+ in.ReadVec(strength);
+ in.Skip(Token::COMMA);
+ in.ReadVec(extent.min);
+ in.Skip(Token::COMMA);
+ in.ReadVec(extent.max);
+ in.Skip(Token::PARENTHESIS_CLOSE);
+ extent.Adjust();
+ return std::unique_ptr<BlockGravity>(new CuboidFieldGravity(strength, extent));
+ } else {
+ throw std::runtime_error("unknown gravity type: " + type);
+ }
+}
+
+