fix(runtime): prevent IK constraint pose pop from stale FK base (#13301) e17fbf4aa8

Co-authored-by: hernan <hernan@rive.app>

.rive_head

diff --git a/.rive_head b/.rive_head
index 348efd1..6143029 100644
--- a/.rive_head
+++ b/.rive_head
@@ -1 +1 @@
-289d353ac57d5bd7b7264b258745abc3d9c8a8b6
+e17fbf4aa8f011ec64e94b982b4e7aa7e9874010

src/constraints/ik_constraint.cpp

diff --git a/src/constraints/ik_constraint.cpp b/src/constraints/ik_constraint.cpp
index 666f1c1..d56a5e2 100644
--- a/src/constraints/ik_constraint.cpp
+++ b/src/constraints/ik_constraint.cpp
@@ -232,9 +232,9 @@
         const Mat2D& parentWorld = getParentWorld(*bone);
         item.parentWorldInverse = parentWorld.invertOrIdentity();
 
-        Mat2D& boneTransform = bone->mutableTransform();
-        boneTransform = item.parentWorldInverse * bone->worldTransform();
-        item.transformComponents = boneTransform.decompose();
+        bone->updateTransform();
+        bone->mutableWorldTransform() = parentWorld * bone->transform();
+        item.transformComponents = bone->transform().decompose();
     }
 
     int count = (int)m_FkChain.size();

tests/unit_tests/assets/ik_anim_test.riv

diff --git a/tests/unit_tests/assets/ik_anim_test.riv b/tests/unit_tests/assets/ik_anim_test.riv
new file mode 100644
index 0000000..4ddc70a
--- /dev/null
+++ b/tests/unit_tests/assets/ik_anim_test.riv
Binary files differ

tests/unit_tests/runtime/ik_constraint_test.cpp

diff --git a/tests/unit_tests/runtime/ik_constraint_test.cpp b/tests/unit_tests/runtime/ik_constraint_test.cpp
index 26f1f4c..868ab91 100644
--- a/tests/unit_tests/runtime/ik_constraint_test.cpp
+++ b/tests/unit_tests/runtime/ik_constraint_test.cpp
@@ -7,6 +7,8 @@
 #include <rive/bones/bone.hpp>
 #include "rive_file_reader.hpp"
 #include "rive_testing.hpp"
+#include "utils/serializing_factory.hpp"
+#include "rive/animation/state_machine_instance.hpp"
 #include <cstdio>
 
 TEST_CASE("ik with skinned bones orders correctly", "[file]")
@@ -36,3 +38,37 @@
     REQUIRE(skin->graphOrder() > one->graphOrder());
     REQUIRE(skin->graphOrder() > two->graphOrder());
 }
+
+TEST_CASE("IK constraint with non full strength", "[silver]")
+{
+    rive::SerializingFactory silver;
+    auto file = ReadRiveFile("assets/ik_anim_test.riv", &silver);
+
+    auto artboard = file->artboardDefault();
+
+    silver.frameSize(artboard->width(), artboard->height());
+
+    auto renderer = silver.makeRenderer();
+
+    auto stateMachine = artboard->stateMachineAt(0);
+
+    auto vmi = file->createViewModelInstance(artboard.get()->viewModelId(), 0);
+
+    stateMachine->bindViewModelInstance(vmi);
+    stateMachine->advanceAndApply(0);
+    artboard->draw(renderer.get());
+
+    silver.addFrame();
+    stateMachine->advanceAndApply(0.1f);
+    artboard->draw(renderer.get());
+
+    int frames = (int)(2.0f / 0.5f);
+    for (int i = 0; i < frames; i++)
+    {
+        silver.addFrame();
+        stateMachine->advanceAndApply(0.5f);
+        artboard->draw(renderer.get());
+    }
+
+    CHECK(silver.matches("ik_anim_test"));
+}

tests/unit_tests/silvers/ik_anim_test.sriv

diff --git a/tests/unit_tests/silvers/ik_anim_test.sriv b/tests/unit_tests/silvers/ik_anim_test.sriv
new file mode 100644
index 0000000..9a6f397
--- /dev/null
+++ b/tests/unit_tests/silvers/ik_anim_test.sriv
Binary files differ