From 2eadedbfaf20fb727d6c3364496074f716ff5e16 Mon Sep 17 00:00:00 2001
From: Ryan Blue <ryanzblue@gmail.com>
Date: Mon, 22 Apr 2024 01:36:22 -0400
Subject: [PATCH] [apriltag] Cache layout loaded from AprilTagFields resource
 json (#6385)

---
 .../wpi/first/apriltag/AprilTagFieldLayout.java | 17 ++++++++++++-----
 .../edu/wpi/first/apriltag/AprilTagFields.java  |  2 ++
 2 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/apriltag/src/main/java/edu/wpi/first/apriltag/AprilTagFieldLayout.java b/apriltag/src/main/java/edu/wpi/first/apriltag/AprilTagFieldLayout.java
index d2a5dd1cdfe..bae5007f545 100644
--- a/apriltag/src/main/java/edu/wpi/first/apriltag/AprilTagFieldLayout.java
+++ b/apriltag/src/main/java/edu/wpi/first/apriltag/AprilTagFieldLayout.java
@@ -230,12 +230,19 @@ public void serialize(Path path) throws IOException {
    * @throws UncheckedIOException If the layout does not exist.
    */
   public static AprilTagFieldLayout loadField(AprilTagFields field) {
-    try {
-      return loadFromResource(field.m_resourceFile);
-    } catch (IOException e) {
-      throw new UncheckedIOException(
-          "Could not load AprilTagFieldLayout from " + field.m_resourceFile, e);
+    if (field.m_fieldLayout == null) {
+      try {
+        field.m_fieldLayout = loadFromResource(field.m_resourceFile);
+      } catch (IOException e) {
+        throw new UncheckedIOException(
+            "Could not load AprilTagFieldLayout from " + field.m_resourceFile, e);
+      }
     }
+    // Copy layout because the layout's origin is mutable
+    return new AprilTagFieldLayout(
+        field.m_fieldLayout.getTags(),
+        field.m_fieldLayout.getFieldLength(),
+        field.m_fieldLayout.getFieldWidth());
   }
 
   /**
diff --git a/apriltag/src/main/java/edu/wpi/first/apriltag/AprilTagFields.java b/apriltag/src/main/java/edu/wpi/first/apriltag/AprilTagFields.java
index 776050c2749..c569a9c55ff 100644
--- a/apriltag/src/main/java/edu/wpi/first/apriltag/AprilTagFields.java
+++ b/apriltag/src/main/java/edu/wpi/first/apriltag/AprilTagFields.java
@@ -24,6 +24,8 @@ public enum AprilTagFields {
   /** Resource filename. */
   public final String m_resourceFile;
 
+  AprilTagFieldLayout m_fieldLayout;
+
   AprilTagFields(String resourceFile) {
     m_resourceFile = kBaseResourceDir + resourceFile;
   }