private XmlElement MakeAnimationNode(XmlDocument scml, int id, ProcessingAnimation animation)
        {
            XmlElement animationElement = scml.CreateElement("animation");

            animationElement.SetAttribute("id", id.ToString());
            animationElement.SetAttribute("name", animation.Name);
            animationElement.SetAttribute("length", animation.Length.ToString());
            animationElement.SetAttribute("interval", animation.Step.ToString());
            XmlElement mainlineElement = scml.CreateElement("mainline");

            for (int j = 0; j < animation.FrameArray[0].Count; j++)
            {
                XmlElement keyElement = scml.CreateElement("key");
                keyElement.SetAttribute("id", j.ToString());
                keyElement.SetAttribute("time", (j * animation.Step).ToString());
                for (int i = 0; i < animation.FrameArray.Count; i++)
                {
                    if (animation.FrameArray[i][j] != null)
                    {
                        ProcessingFrame frame = animation.FrameArray[i][j];
                        ChildType       type  = animation.InfoProvider.GetType(i);
                        if (type == ChildType.Bone)
                        {
                            XmlElement boneElement = scml.CreateElement("bone_ref");
                            boneElement.SetAttribute("id", i.ToString());
                            boneElement.SetAttribute("timeline", i.ToString());
                            boneElement.SetAttribute("key", j.ToString());
                            if (frame.ParentId != -1)
                            {
                                boneElement.SetAttribute("parent", frame.ParentId.ToString());
                            }
                            keyElement.AppendChild(boneElement);
                        }
                        else if (type == ChildType.Sprite)
                        {
                            XmlElement objectElement = scml.CreateElement("object_ref");
                            objectElement.SetAttribute("id", i.ToString());
                            objectElement.SetAttribute("timeline", i.ToString());
                            objectElement.SetAttribute("key", j.ToString());
                            if (frame.ParentId != -1)
                            {
                                objectElement.SetAttribute("parent", frame.ParentId.ToString());
                            }
                            objectElement.SetAttribute("z_index", frame.ZIndex.ToString());
                            keyElement.AppendChild(objectElement);
                        }
                    }
                }
                mainlineElement.AppendChild(keyElement);
            }
            animationElement.AppendChild(mainlineElement);
            for (int i = 0; i < animation.FrameArray.Count; i++)
            {
                XmlElement timelineElement = scml.CreateElement("timeline");
                timelineElement.SetAttribute("id", i.ToString());
                timelineElement.SetAttribute("name", animation.InfoProvider.GetName(i));
                for (int j = 0; j < animation.FrameArray[0].Count; j++)
                {
                    if (animation.FrameArray[i][j] != null)
                    {
                        XmlElement keyElement = scml.CreateElement("key");
                        keyElement.SetAttribute("id", j.ToString());
                        keyElement.SetAttribute("time", (j * animation.Step).ToString());
                        ProcessingFrame frame = animation.FrameArray[i][j];
                        ChildType       type  = animation.InfoProvider.GetType(i);
                        if (type == ChildType.Bone)
                        {
                            XmlElement boneElement = scml.CreateElement("bone");
                            boneElement.SetAttribute("x", frame.X.ToString());
                            boneElement.SetAttribute("y", frame.Y.ToString());
                            boneElement.SetAttribute("angle", frame.Angle.ToString());
                            boneElement.SetAttribute("scale_x", frame.ScaleX.ToString());
                            boneElement.SetAttribute("scale_y", frame.ScaleY.ToString());
                            keyElement.AppendChild(boneElement);
                        }
                        else if (type == ChildType.Sprite)
                        {
                            XmlElement objectElement = scml.CreateElement("object");
                            objectElement.SetAttribute("folder", frame.Folder.ToString());
                            objectElement.SetAttribute("file", frame.File.ToString());
                            objectElement.SetAttribute("x", frame.X.ToString());
                            objectElement.SetAttribute("y", frame.Y.ToString());
                            objectElement.SetAttribute("angle", frame.Angle.ToString());
                            objectElement.SetAttribute("scale_x", frame.ScaleX.ToString());
                            objectElement.SetAttribute("scale_y", frame.ScaleY.ToString());
                            keyElement.AppendChild(objectElement);
                        }
                        timelineElement.AppendChild(keyElement);
                    }
                }
                animationElement.AppendChild(timelineElement);
            }
            return(animationElement);
        }
        private ProcessingAnimation ParseAnimation(XmlDocument scml, XmlElement animation)
        {
            string          name         = animation.GetAttribute("name");
            int             length       = int.Parse(animation.GetAttribute("length"));
            int             interval     = int.Parse(animation.GetAttribute("interval"));
            TimelineInfoMap infoProvider = new TimelineInfoMap(scml, name);

            /* rename the ids to match timelines in "id" and "parent" */
            IdRename(animation, infoProvider);

            /* build the frame array - description is in Alternate.Animation */
            List <List <ProcessingFrame> > frameArray = new List <List <ProcessingFrame> >();
            /* count of frames to know how large the frame array should be */
            int numberOfFrames = length / interval + 1;

            /* for each sprite and bone id a list of frames is created */
            for (int i = 0; i < infoProvider.Size(); i++)
            {
                List <ProcessingFrame> frames = new List <ProcessingFrame>();
                for (int j = 0; j < numberOfFrames; j++)
                {
                    /* start out with a completely empty frame array so it can later be populated
                     * with the existing data and then finally with the interpolated data */
                    frames.Add(null);
                }
                frameArray.Add(frames);
            }

            /* error checking to see if the animation doesn't have every frame snapped to an interval
             * because ONI expects every frame to have a consistent interval so if the frames aren't
             * snapped they will be placed wrong */
            var hasBrokenSnapping = false;
            var brokenAnims       = new HashSet <string>();

            /* error checking if user has accidentally used pivots in timeline rather than setting pivot on original sprite */
            var hasPivotsSpecifiedInTimeline = false;
            var pivotAnims = new HashSet <string>();

            /* read all the data from mainline
             * oddly it is not needed to read which timeline key frame is associated
             * with each mainline key frame since the timline key frames contain timing
             * information which can be used to exactly place them in the array since
             * we force snapping to intervals for ONI animations */
            XmlElement mainline = GetFirstChildByName(animation, "mainline");

            foreach (XmlNode keyNode in mainline.ChildNodes)
            {
                if (keyNode is XmlElement && keyNode.Name.Equals("key"))
                {
                    int        time       = 0;
                    XmlElement keyElement = (XmlElement)keyNode;
                    if (keyElement.HasAttribute("time"))
                    {
                        time = int.Parse(keyElement.GetAttribute("time"));
                    }
                    if (time % interval != 0)
                    {
                        Logger.Warn(
                            $"While parsing animation \"{name}\", found broken snapping in the mainline: it is time {time} ms that is not a multiple of snapping interval {interval} ms.");
                        hasBrokenSnapping = true;
                        brokenAnims.Add(name);
                    }

                    /* scale the time by the interval between frames to figure out which
                     * frame index in the array this goes to */
                    int frameIndex = time / interval;
                    foreach (XmlNode refNode in keyNode.ChildNodes)
                    {
                        if (refNode is XmlElement &&
                            (refNode.Name.Equals("object_ref") || refNode.Name.Equals("bone_ref")))
                        {
                            XmlElement refElement = (XmlElement)refNode;
                            /* the call to IdRename ensures that the ids on each ref now match the actual index in the array */
                            int id     = int.Parse(refElement.GetAttribute("id"));
                            int zIndex = 0;
                            if (refElement.HasAttribute("z_index")) /* will always be true for sprites never true for bones */
                            {
                                zIndex = int.Parse(refElement.GetAttribute("z_index"));
                            }
                            int parent = -1;
                            if (refElement.HasAttribute("parent")) /* optional for both sprites and bones */
                            {
                                parent = int.Parse(refElement.GetAttribute("parent"));
                            }
                            /* set this frame to contain the data stored in the mainline */
                            frameArray[id][frameIndex] = new ProcessingFrame(parent, zIndex);
                        }
                    }
                }
            }

            /* read all the data from each timeline and use it to further populate the data of each frame */
            foreach (XmlNode timelineNode in animation.ChildNodes)
            {
                if (timelineNode is XmlElement && timelineNode.Name.Equals("timeline"))
                {
                    XmlElement timelineElement = (XmlElement)timelineNode;
                    int        timeline        = int.Parse(timelineElement.GetAttribute("id"));
                    int        timelineIndex   = infoProvider.GetId(timeline);
                    float      x     = 0;
                    float      y     = 0;
                    float      angle = 0;
                    foreach (XmlNode keyNode in timelineNode.ChildNodes)
                    {
                        if (keyNode is XmlElement && keyNode.Name.Equals("key"))
                        {
                            XmlElement keyElement = (XmlElement)keyNode;
                            int        time       = 0;
                            if (keyElement.HasAttribute("time"))
                            {
                                time = int.Parse(keyElement.GetAttribute("time"));
                            }
                            if (time % interval != 0)
                            {
                                Logger.Warn(
                                    $"While parsing animation \"{name}\", found broken snapping at timeline {timeline}: it is time {time} ms that is not a multiple of snapping interval {interval} ms.");
                                hasBrokenSnapping = true;
                                brokenAnims.Add(name);
                            }
                            int        frameIndex = time / interval;
                            XmlElement child      = GetFirstChildByName(keyElement, "object");
                            if (child == null)
                            {
                                child = GetFirstChildByName(keyElement, "bone");
                            }
                            if (child == null)
                            {
                                throw new ArgumentException("Found timeline key without child object or bone");
                            }
                            int folder = -1;
                            if (child.HasAttribute("folder"))
                            {
                                folder = int.Parse(child.GetAttribute("folder"));
                            }
                            int file = -1;
                            if (child.HasAttribute("file"))
                            {
                                file = int.Parse(child.GetAttribute("file"));
                            }
                            if (child.HasAttribute("x"))
                            {
                                x = float.Parse(child.GetAttribute("x"));
                            }
                            if (child.HasAttribute("y"))
                            {
                                y = float.Parse(child.GetAttribute("y"));
                            }
                            if (child.HasAttribute("angle"))
                            {
                                angle = float.Parse(child.GetAttribute("angle"));
                            }
                            float scaleX = 1.0f;
                            if (child.HasAttribute("scale_x"))
                            {
                                scaleX = float.Parse(child.GetAttribute("scale_x"));
                            }
                            float scaleY = 1.0f;
                            if (child.HasAttribute("scale_y"))
                            {
                                scaleY = float.Parse(child.GetAttribute("scale_y"));
                            }
                            frameArray[timelineIndex][frameIndex].Populate(folder, file, x, y, angle, scaleX, scaleY);

                            if (child.HasAttribute("pivot_x") || child.HasAttribute("pivot_y"))
                            {
                                hasPivotsSpecifiedInTimeline = true;
                                pivotAnims.Add(name);
                            }
                        }
                    }
                }
            }

            if (hasBrokenSnapping)
            {
                var anims = brokenAnims.ToList().Join();
                throw new ProjectParseException(
                          $"SCML format exception: The timelines in anims {anims} had frames at times not snapped to the running interval {interval} ms. Aborting read.");
            }

            if (hasPivotsSpecifiedInTimeline)
            {
                var anims = pivotAnims.ToList().Join();
                throw new ProjectParseException(
                          $"SCML format exception: There were pivot points specified in timelines rather than only on the sprites in anims {anims}. Aborting read.");
            }

            /* determine which frames need to be interpolated by checking which frames are key frames in the mainline */
            List <bool> keyFrames = new List <bool>();

            for (int i = 0; i < numberOfFrames; i++)
            {
                keyFrames.Add(false);
            }
            foreach (XmlNode keyNode in mainline.ChildNodes)
            {
                if (keyNode is XmlElement && keyNode.Name.Equals("key"))
                {
                    int        time       = 0;
                    XmlElement keyElement = (XmlElement)keyNode;
                    if (keyElement.HasAttribute("time"))
                    {
                        time = int.Parse(keyElement.GetAttribute("time"));
                    }

                    /* scale the time by the interval between frames to figure out which
                     * frame index in the array this goes to */
                    int frameIndex = time / interval;
                    /* now we know this particular time step is a key frame in the mainline */
                    keyFrames[frameIndex] = true;
                }
            }

            /* create an additional array that indicates presence of each timeline on a per-frame basis */
            List <List <bool> > presenceArray = new List <List <bool> >();

            for (int i = 0; i < infoProvider.Size(); i++)
            {
                List <bool> presences = new List <bool>();
                for (int j = 0; j < numberOfFrames; j++)
                {
                    /* start out with a completely empty presence array so it can later be populated
                     * with the existing data and then finally with the interpolated data */
                    presences.Add(false);
                }
                presenceArray.Add(presences);
            }
            for (int i = 0; i < infoProvider.Size(); i++)
            {
                bool currentPresence = false;
                for (int j = 0; j < numberOfFrames; j++)
                {
                    /* if this frame is a key frame then update the current presence based on if there
                     * is a frame populated at this location */
                    if (keyFrames[j])
                    {
                        currentPresence = (frameArray[i][j] != null);
                    }
                    presenceArray[i][j] = currentPresence;
                }
                for (int j = 0; j < numberOfFrames; j++)
                {
                    /* if this frame is a key frame then update the current presence based on if there
                     * is a frame populated at this location */
                    if (keyFrames[j])
                    {
                        currentPresence = (frameArray[i][j] != null);
                    }
                    presenceArray[i][j] = currentPresence;
                }

                /* executing the loop twice is the most straightforward way to ensure that a keyframe at the end
                 * of the timeline wraps around to the front of the timeline
                 * this does mess with animations that aren't looped that don't have keyframes at time = 0 but that just doesn't make
                 * much sense (who wouldn't keyframe at time = 0 for a non-looping animation!)
                 * so I'll just document that and ignore that problem for now */
            }

            /* for every frame with presence in the array set to true that still has a null frame
             * interpolate the missing frame */
            for (int i = 0; i < infoProvider.Size(); i++)
            {
                ProcessingFrame beforeFrame      = null;
                ProcessingFrame afterFrame       = null;
                int             beforeFrameIndex = -1;
                int             afterFrameIndex  = -1;
                for (int j = 0; j < numberOfFrames; j++)
                {
                    /* skip this frame if it isn't supposed to be present */
                    if (!presenceArray[i][j])
                    {
                        continue;
                    }

                    /* if this frame exists and is populated then it will be used
                     * as the before frame */
                    if (frameArray[i][j] != null && frameArray[i][j].IsPopulated())
                    {
                        beforeFrame      = frameArray[i][j];
                        beforeFrameIndex = j;

                        /* probe forward to find the after array when a before array is found
                         * will use a endless loop because eventually at least we know we will
                         * terminate when it hits the exact same before array */
                        int jPrime = j + 1;
                        if (jPrime >= numberOfFrames)
                        {
                            jPrime = 0;
                        }
                        while (presenceArray[i][jPrime])
                        {
                            if (frameArray[i][jPrime] != null && frameArray[i][jPrime].IsPopulated())
                            {
                                afterFrame      = frameArray[i][jPrime];
                                afterFrameIndex = jPrime;
                                break;
                            }
                            jPrime++;
                            if (jPrime >= numberOfFrames)
                            {
                                jPrime = 0;
                            }
                        }

                        /* if we found a before frame but couldn't find an after frame this means that there was a frame that is completely defined
                         * but there are more frames that need to be interpolated from this frame only
                         * since this is the only frame, spriter interprets this frame as being the frame used for all of the interpolated positions
                         * in which this sprite exists */
                        if (afterFrame == null)
                        {
                            Logger.Debug("Could not find after frame to interpolate between. Interpreting this to mean that this frame is expected to take the entire duration of the timeline.");
                            afterFrame      = beforeFrame;
                            afterFrameIndex = beforeFrameIndex;
                        }
                    }
                    else if (beforeFrame != null && afterFrame != null)
                    {
                        float x = LinearInterpolate(beforeFrame.X, afterFrame.X, beforeFrameIndex,
                                                    afterFrameIndex + ((afterFrameIndex < beforeFrameIndex) ? numberOfFrames : 0), j);
                        float y = LinearInterpolate(beforeFrame.Y, afterFrame.Y, beforeFrameIndex,
                                                    afterFrameIndex + ((afterFrameIndex < beforeFrameIndex) ? numberOfFrames : 0), j);
                        float angle = LinearInterpolateAngle(beforeFrame.Angle, afterFrame.Angle, beforeFrameIndex,
                                                             afterFrameIndex + ((afterFrameIndex < beforeFrameIndex) ? numberOfFrames : 0), j);
                        float xScale = LinearInterpolate(beforeFrame.ScaleX, afterFrame.ScaleX, beforeFrameIndex,
                                                         afterFrameIndex + ((afterFrameIndex < beforeFrameIndex) ? numberOfFrames : 0), j);
                        float yScale = LinearInterpolate(beforeFrame.ScaleY, afterFrame.ScaleY, beforeFrameIndex,
                                                         afterFrameIndex + ((afterFrameIndex < beforeFrameIndex) ? numberOfFrames : 0), j);
                        if (frameArray[i][j] == null)
                        {
                            frameArray[i][j] = new ProcessingFrame(beforeFrame.ParentId, beforeFrame.ZIndex);
                        }
                        frameArray[i][j].Populate(beforeFrame.Folder, beforeFrame.File, x, y, angle, xScale, yScale);
                    }
                }
            }
            for (int i = 0; i < infoProvider.Size(); i++)
            {
                ProcessingFrame beforeFrame      = null;
                ProcessingFrame afterFrame       = null;
                int             beforeFrameIndex = -1;
                int             afterFrameIndex  = -1;
                for (int j = 0; j < numberOfFrames; j++)
                {
                    /* skip this frame if it isn't supposed to be present */
                    if (!presenceArray[i][j])
                    {
                        continue;
                    }

                    /* if this frame exists and is populated then it will be used
                     * as the before frame */
                    if (frameArray[i][j] != null && frameArray[i][j].IsPopulated())
                    {
                        beforeFrame      = frameArray[i][j];
                        beforeFrameIndex = j;

                        /* probe forward to find the after array when a before array is found
                         * will use a endless loop because eventually at least we know we will
                         * terminate when it hits the exact same before array */
                        int jPrime = j + 1;
                        if (jPrime >= numberOfFrames)
                        {
                            jPrime = 0;
                        }
                        while (presenceArray[i][jPrime])
                        {
                            if (frameArray[i][jPrime] != null && frameArray[i][jPrime].IsPopulated())
                            {
                                afterFrame      = frameArray[i][jPrime];
                                afterFrameIndex = jPrime;
                                break;
                            }
                            jPrime++;
                            if (jPrime >= numberOfFrames)
                            {
                                jPrime = 0;
                            }
                        }

                        /* if we found a before frame but couldn't find an after frame this means that there was a frame that is completely defined
                         * but there are more frames that need to be interpolated from this frame only
                         * since this is the only frame, spriter interprets this frame as being the frame used for all of the interpolated positions
                         * in which this sprite exists */
                        if (afterFrame == null)
                        {
                            Logger.Debug("Could not find after frame to interpolate between. Interpreting this to mean that this frame is expected to take the entire duration of the timeline.");
                            afterFrame      = beforeFrame;
                            afterFrameIndex = beforeFrameIndex;
                        }
                    }
                    else if (beforeFrame != null && afterFrame != null)
                    {
                        float x = LinearInterpolate(beforeFrame.X, afterFrame.X, beforeFrameIndex,
                                                    afterFrameIndex + ((afterFrameIndex < beforeFrameIndex) ? numberOfFrames : 0), j);
                        float y = LinearInterpolate(beforeFrame.Y, afterFrame.Y, beforeFrameIndex,
                                                    afterFrameIndex + ((afterFrameIndex < beforeFrameIndex) ? numberOfFrames : 0), j);
                        float angle = LinearInterpolateAngle(beforeFrame.Angle, afterFrame.Angle, beforeFrameIndex,
                                                             afterFrameIndex + ((afterFrameIndex < beforeFrameIndex) ? numberOfFrames : 0), j);
                        float xScale = LinearInterpolate(beforeFrame.ScaleX, afterFrame.ScaleX, beforeFrameIndex,
                                                         afterFrameIndex + ((afterFrameIndex < beforeFrameIndex) ? numberOfFrames : 0), j);
                        float yScale = LinearInterpolate(beforeFrame.ScaleY, afterFrame.ScaleY, beforeFrameIndex,
                                                         afterFrameIndex + ((afterFrameIndex < beforeFrameIndex) ? numberOfFrames : 0), j);
                        if (frameArray[i][j] == null)
                        {
                            frameArray[i][j] = new ProcessingFrame(beforeFrame.ParentId, beforeFrame.ZIndex);
                        }
                        frameArray[i][j].Populate(beforeFrame.Folder, beforeFrame.File, x, y, angle, xScale, yScale);
                    }
                }
            }
            /* interpolation is run twice to fix issue where time = 0 is not key frame */

            return(new ProcessingAnimation(name, interval, length, frameArray, infoProvider));
        }