Castle Animation Frames (castle-anim-frames) file format

<?xml version="1.0"?>
<animations             // Root node should be "animations".
                        // It should contain any number (at least one)
                        // "animation" nodes inside.
                        // For backward compatibility,
                        // old (single-animation) files may also
                        // use "animation" as the root node.

  <animation              // A single animation.
                          // All it's attributes are optional
                          // (default values are shown below).
                          // Some of it's attributes should be treated like a
                          // "hint for the renderer". General programs like
                          // Castle Model Viewer may honor them,
                          // but more specialized programs (like "The Castle"
                          // game) may ignore them, since "they know better".

    name="animation"      // Animation name.
                          // To be used e.g. with TCastleScene.PlayAnimation.

    scenes_per_time="30"  // If the animation will be "baked":
                          //
                          // Suggested number of scenes per time to be generated.
                          // This is a hint for the renderer -- by default it's
                          // 30, but it may be ignored. Larger values make
                          // animation smoother, but also much more memory consuming.
                          // Special value 0 is allowed here, and means
                          // that animation will simply show each <frame>,
                          // suddenly changing into the next <frame>,
                          // without any smoothing of transitions with
                          // intermediate scenes.

    equality_epsilon="0.001"
                          // If the animation will be "baked":
                          //
                          // Epsilon to use when comparing animation frames
                          // and deciding which parts didn't move at all between
                          // two adjacent frames. You can set this even to literal
                          // "0.0", but this may cause a lot of memory to be wasted
                          // when loading large animation. It's better to set
                          // this to some very small value -- so small that you're
                          // sure that user will not notice such small move
                          // anyway.

    loop="false"          // Should the animation loop? This is a hint for
                          // the renderer, and may be ignored. Allowed values
                          // are "false" and "true", not case-sensitive.
                          // When this animation is used for creature/item in game,
                          // this is ignored.

    backwards="false"     // Should the animation go backwards after going
                          // forward? Allowed values
                          // are "false" and "true", not case-sensitive.
                          // When this animation is used for creature/item in game,
                          // this is not ignored.
  >

    // A number of <frame> nodes should follow. At least one is required.
    // Note that exactly one <frame> node will actually define a still scene,
    // you need at least 2 frames if you want a real animation.

    <frame

      url="file_1.x3d" // This specifies the URL from which to load this
                       // animation frame. Any 3D file format is allowed here.
                       // There is also a deprecated attribute "file_name"
                       // that means the same as "url".
                       //
                       // This attribute may be omitted, in which case
                       // we expect the <frame> element to contain the model
                       // inlined, in format indicated by mime_type.

      mime_type="model/x3d+xml"
                       // In case the frame content is inlined
                       // (url is not set), this indicates the inlined model format.
                       // For now we only allow "model/x3d+xml" (X3D XML)
                       // or "model/gltf+json" (glTF JSON).

      time="0.0"       // This is a required attribute specifying a
                       // time of this frame. For now, all frames
                       // must be specified in the strictly increasing order
                       // of their "time".
                       // This is understood to be in seconds.

      bounding_box_center="0 0 0"
      bounding_box_size="-1 -1 -1"
                       // Bounding box of this animation frame.
                       // Used for collision detection.
                       // Empty if not specified, or if any size
                       // component is negative.
                       //
                       // This is consistent with X3D bboxSize/Center
                       // fields definition e.g. at X3D Group node.
    />

    // For example, assume that the second <frame> node follows.
    // So this defines an animation that changes from
    // file_1.x3d and file_2.x3d in exactly 1 second.

    <frame url="file_2.x3d" time="1.0" />
  </animation>

  // More animations follow, if you want:
  <animation name="another_animation">
    <frame url="another_animation_frame_0.x3d" time="0.0" />
    <frame url="another_animation_frame_1.x3d" time="1.0" />
  </animation>

  <animation name="yet_another_animation">
    <frame url="yet_another_animation_frame_0.x3d" time="0.0" />
    <frame url="yet_another_animation_frame_1.x3d" time="1.0" />
  </animation>
</animations>