Fix ik issue. Fixes rive-app/rive#3313

include/rive/constraints/ik_constraint.hpp

diff --git a/include/rive/constraints/ik_constraint.hpp b/include/rive/constraints/ik_constraint.hpp
index 300d0cf..c6abd1c 100644
--- a/include/rive/constraints/ik_constraint.hpp
+++ b/include/rive/constraints/ik_constraint.hpp
@@ -27,6 +27,7 @@
         void markConstraintDirty() override;
         StatusCode onAddedClean(CoreContext* context) override;
         void constrain(TransformComponent* component) override;
+        void buildDependencies() override;
     };
 } // namespace rive
 

src/constraints/ik_constraint.cpp

diff --git a/src/constraints/ik_constraint.cpp b/src/constraints/ik_constraint.cpp
index 9348d12..3400a5e 100644
--- a/src/constraints/ik_constraint.cpp
+++ b/src/constraints/ik_constraint.cpp
@@ -6,6 +6,17 @@
 
 using namespace rive;
 
+void IKConstraint::buildDependencies() {
+    Super::buildDependencies();
+
+    // IK Constraint needs to depend on the target so that world transform
+    // changes can propagate to the bones (and they can be reset before IK
+    // runs).
+    if (m_Target != nullptr) {
+        m_Target->addDependent(this);
+    }
+}
+
 StatusCode IKConstraint::onAddedClean(CoreContext* context) {
     if (!parent()->is<Bone>()) {
         return StatusCode::InvalidObject;
@@ -104,18 +115,14 @@
     b2->tipWorldTranslation(pB);
     Vec2D pBT(worldTargetTranslation);
 
-    pA  = iworld * pA;
-    pC  = iworld * pC;
-    pB  = iworld * pB;
+    pA = iworld * pA;
+    pC = iworld * pC;
+    pB = iworld * pB;
     pBT = iworld * pBT;
 
     // http://mathworld.wolfram.com/LawofCosines.html
-    Vec2D av = pB  - pC,
-          bv = pC  - pA,
-          cv = pBT - pA;
-    float a = av.length(),
-          b = bv.length(),
-          c = cv.length();
+    Vec2D av = pB - pC, bv = pC - pA, cv = pBT - pA;
+    float a = av.length(), b = bv.length(), c = cv.length();
 
     float A = std::acos(std::max(
         -1.0f, std::min(1.0f, (-a * a + b * b + c * c) / (2.0f * b * c))));
@@ -153,7 +160,8 @@
     constrainRotation(*firstChild, r2);
     if (firstChild != fk2) {
         Bone* bone = fk2->bone;
-        bone->mutableWorldTransform() = getParentWorld(*bone) * bone->transform();
+        bone->mutableWorldTransform() =
+            getParentWorld(*bone) * bone->transform();
     }
 
     // Simple storage, need this for interpolation.

test/ik_test.cpp

diff --git a/test/ik_test.cpp b/test/ik_test.cpp
index ab5eb14..fc4f08a 100644
--- a/test/ik_test.cpp
+++ b/test/ik_test.cpp
@@ -79,3 +79,79 @@
                                    240.1275634765625f,
                                    225.07647705078125f)));
 }
+
+TEST_CASE("ik keeps working after a lot of iterations", "[file]") {
+    RiveFileReader reader("../../test/assets/two_bone_ik.riv");
+    auto artboard = reader.file()->artboard();
+
+    REQUIRE(artboard->find<rive::Shape>("circle a") != nullptr);
+    auto circleA = artboard->find<rive::Shape>("circle a");
+
+    REQUIRE(artboard->find<rive::Shape>("circle b") != nullptr);
+    auto circleB = artboard->find<rive::Shape>("circle b");
+
+    REQUIRE(artboard->find<rive::Bone>("a") != nullptr);
+    auto boneA = artboard->find<rive::Bone>("a");
+
+    REQUIRE(artboard->find<rive::Bone>("b") != nullptr);
+    auto boneB = artboard->find<rive::Bone>("b");
+
+    REQUIRE(artboard->find<rive::Node>("target") != nullptr);
+    auto target = artboard->find<rive::Node>("target");
+
+    REQUIRE(artboard->animation("Animation 1") != nullptr);
+    auto animation = artboard->animation("Animation 1");
+
+    // Make sure dependency structure is correct. Important thing here is to
+    // ensure that circle a is dependent upon the tip of the ik chain (bone b).
+    // circle b is a child of bone b so it'll be there anyway, but may as well
+    // validate.
+    REQUIRE(std::find(boneB->dependents().begin(),
+                      boneB->dependents().end(),
+                      circleA) != boneB->dependents().end());
+    REQUIRE(std::find(boneB->dependents().begin(),
+                      boneB->dependents().end(),
+                      circleB) != boneB->dependents().end());
+
+    for (int i = 0; i < 1000; i++) {
+        animation->apply(artboard, 0.0f, 1.0f);
+        artboard->advance(0.0f);
+        REQUIRE(target->x() == 296.0f);
+        REQUIRE(target->y() == 202.0f);
+        REQUIRE(aboutEqual(boneA->worldTransform(),
+                           rive::Mat2D(0.11632211506366729736328125f,
+                                       -0.993211567401885986328125f,
+                                       0.993211567401885986328125f,
+                                       0.11632211506366729736328125f,
+                                       26.015254974365234375f,
+                                       475.2149658203125f)));
+
+        REQUIRE(aboutEqual(boneB->worldTransform(),
+                           rive::Mat2D(0.974071562290191650390625f,
+                                       0.2262403070926666259765625f,
+                                       -0.2262403070926666259765625f,
+                                       0.974071562290191650390625f,
+                                       64.31568145751953125f,
+                                       148.1883544921875f)));
+
+        animation->apply(artboard, 1.0f, 1.0f);
+        artboard->advance(0.0f);
+        REQUIRE(target->x() == 450.0f);
+        REQUIRE(target->y() == 337.0f);
+        REQUIRE(aboutEqual(boneA->worldTransform(),
+                           rive::Mat2D(0.650279819965362548828125f,
+                                       -0.7596948146820068359375f,
+                                       0.7596948146820068359375f,
+                                       0.650279819965362548828125f,
+                                       26.015254974365234375f,
+                                       475.2149658203125f)));
+
+        REQUIRE(aboutEqual(boneB->worldTransform(),
+                           rive::Mat2D(0.8823678493499755859375f,
+                                       0.470560371875762939453125f,
+                                       -0.47056043148040771484375f,
+                                       0.882367908954620361328125f,
+                                       240.1275634765625f,
+                                       225.07647705078125f)));
+    }
+}
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