Modify Simulate::InjectNoise to set target of exponential decay to value from key_ctrl if a valid key is provided as input.

PiperOrigin-RevId: 813819040
Change-Id: I79508039b17fb3484b71ae0d19614c32adacfa10

simulate/simulate.cc

@@ -2917,7 +2917,7 @@ void Simulate::AddToHistory() {
 }
 
 // inject Brownian noise
-void Simulate::InjectNoise() {
+void Simulate::InjectNoise(int key) {
   // no noise, return
   if (ctrl_noise_std <= 0) {
     return;
@@ -2936,6 +2936,11 @@ void Simulate::InjectNoise() {
       halfrange = 0.5 * (top - bottom);  // scales noise
     }
 
+    // overwrite midpoint with keyframe, if given
+    if (key >= 0) {
+      midpoint = m_->key_ctrl[key*m_->nu+i];
+    }
+
     // exponential convergence to midpoint at ctrl_noise_rate
     d_->ctrl[i] = rate * d_->ctrl[i] + (1-rate) * midpoint;