Added validator for camera animations to have a keyframe at frame 0

Unreal shifts the first keyframe to frame 0. Forcing the camera to have a keyframe at frame 0 will ensure that the animation will be the same in Unreal and Blender.

openpype/hosts/blender/plugins/publish/validate_camera_zero_keyframe.py

@@ -0,0 +1,48 @@
+from typing import List
+
+import mathutils
+
+import pyblish.api
+import openpype.hosts.blender.api.action
+
+
+class ValidateCameraZeroKeyframe(pyblish.api.InstancePlugin):
+    """Camera must have a keyframe at frame 0.
+
+    Unreal shifts the first keyframe to frame 0. Forcing the camera to have
+    a keyframe at frame 0 will ensure that the animation will be the same
+    in Unreal and Blender.
+    """
+
+    order = openpype.api.ValidateContentsOrder
+    hosts = ["blender"]
+    families = ["camera"]
+    category = "geometry"
+    version = (0, 1, 0)
+    label = "Zero Keyframe"
+    actions = [openpype.hosts.blender.api.action.SelectInvalidAction]
+
+    _identity = mathutils.Matrix()
+
+    @classmethod
+    def get_invalid(cls, instance) -> List:
+        invalid = []
+        for obj in [obj for obj in instance]:
+            if obj.type == "CAMERA":
+                if obj.animation_data and obj.animation_data.action:
+                    action = obj.animation_data.action
+                    frames_set = set()
+                    for fcu in action.fcurves:
+                        for kp in fcu.keyframe_points:
+                            frames_set.add(kp.co[0])
+                    frames = list(frames_set)
+                    frames.sort()
+                    if frames[0] != 0.0:
+                        invalid.append(obj)
+        return invalid
+
+    def process(self, instance):
+        invalid = self.get_invalid(instance)
+        if invalid:
+            raise RuntimeError(
+                f"Object found in instance is not in Object Mode: {invalid}")