One of the issues I had to resolve during the development of our next game was slow loading times on WP8. After some investigation I figure that about half of the time was spent on loading models with skinning information.
I use the code from the CPU Skinning sample. The sample demonstrate how to efficiently do animations on mobile devices which means all other aspects are left as simple as possible so you can adapt it to your needs easily. So, it comes as no surprise that the code depends on automatic serialization (reflection) which is not very efficient. Since we are going to talk about content loading on XNA / MonoGame this post apply to traditional GPU-skinning as well.
Most of the CPU circles were wasted on serializing the list of Keyframes in AnimationClip. To resolve this we can write our own serializer. If you think this doesn't worth doing then take a look at the numbers below...
| Platform |
Reader |
Loading Time |
| XNA |
automatic serialization |
03,826 sec |
| custom AnimationClipReader |
01,970 sec |
| MonoGame |
automatic serialization |
14,263 sec |
| custom AnimationClipReader |
07,284 sec |
(Lumia 620). You can clearly see a drop by ~50% (Twice as Fast!).
The produced .xnb are also a bit smaller.
he first step is to write a new ContentTypeWriter. Open the CpuSkinningPipelineExtensions project and add a new file named AnimationClipWriter.cs. Copy-paste the following code.
using CpuSkinningDataTypes;
using Microsoft.Xna.Framework.Content.Pipeline;
using Microsoft.Xna.Framework.Content.Pipeline.Serialization.Compiler;
using System;
using System.Collections.Generic;
namespace CpuSkinningPipelineExtensions
{
/// <summary>
/// Writes out a KeyframeContent object to an XNB file to be read in as
/// a Keyframe.
/// </summary>
[ContentTypeWriter]
class AnimationClipWriter : ContentTypeWriter<AnimationClip>
{
protected override void Write(ContentWriter output, AnimationClip value)
{
WriteDuration(output, value.Duration);
WriteKeyframes(output, value.Keyframes);
}
private void WriteDuration(ContentWriter output, TimeSpan duration)
{
output.Write(duration.Ticks);
}
private void WriteKeyframes(ContentWriter output, IList<Keyframe> keyframes)
{
Int32 count = keyframes.Count;
output.Write((Int32)count);
for (int i = 0; i < count; i++)
{
Keyframe keyframe = keyframes[i];
output.Write(keyframe.Bone);
output.Write(keyframe.Time.Ticks);
output.Write(keyframe.Transform);
}
return;
}
public override string GetRuntimeType(TargetPlatform targetPlatform)
{
return "CpuSkinningDataTypes.AnimationClip, CpuSkinningDataTypes";
}
public override string GetRuntimeReader(TargetPlatform targetPlatform)
{
return "CpuSkinningDataTypes.AnimationClipReader, CpuSkinningDataTypes";
}
}
}
At this point you should rebuild the Content to get the new .XNB.
Next, Open the CpuSkinningDataTypes project and add a new file named AnimationClipReader.cs. Copy-paste the following code.
using System.Collections.Generic;
using System.Collections.ObjectModel;
using Microsoft.Xna.Framework.Content;
using Microsoft.Xna.Framework.Graphics;
using Microsoft.Xna.Framework;
using System;
namespace CpuSkinningDataTypes
{
/// <summary>
/// A custom reader to read Keyframe.
/// </summary>
public class AnimationClipReader : ContentTypeReader<AnimationClip>
{
protected override AnimationClip Read(ContentReader input, AnimationClip existingInstance)
{
AnimationClip animationClip = existingInstance;
if (existingInstance == null)
{
TimeSpan duration = ReadDuration(input);
List<Keyframe> keyframes = ReadKeyframes(input, null);
animationClip = new AnimationClip(duration, keyframes);
}
else
{
animationClip.Duration = ReadDuration(input);
ReadKeyframes(input, animationClip.Keyframes);
}
return animationClip;
}
private TimeSpan ReadDuration(ContentReader input)
{
return new TimeSpan(input.ReadInt64());
}
private List<Keyframe> ReadKeyframes(ContentReader input, List<Keyframe> existingInstance)
{
List<Keyframe> keyframes = existingInstance;
int count = input.ReadInt32();
if (keyframes == null)
keyframes = new List<Keyframe>(count);
for (int i = 0; i < count; i++)
{
Keyframe keyframe = new Keyframe();
keyframe.Bone = input.ReadInt32();
keyframe.Time = new TimeSpan(input.ReadInt64());
keyframe.Transform = input.ReadMatrix();
if (existingInstance == null)
keyframes.Add(keyframe);
else
keyframes[i] = keyframe;
}
return keyframes;
}
}
}
At this point you must make a few minor changes to AnimationClip & Keyframe classes.
Open AnimationClip.cs and change the access modifier of Duration to internal protected.
public TimeSpan Duration { get; internal protected set; }
Now, open Keyframe.cs and replace all private modifiers to internal.
public class Keyframe
{
public int Bone { get; internal set; }
public TimeSpan Time { get; internal set; }
public Matrix Transform { get; internal set; }
internal Keyframe() {}
}
That's it!
If you want to know more about how content serialization works,
see: XNA custom content writer/reader part 1: Introduction.
The .zip file below has some extra changes to correctly reload the model after Resuming under WP8/MonoGame. If you need these changes, make sure to copy both the CpuSkinnedModelWriter.cs / CpuSkinnedModelReader.cs to your project and then rebuild your content.
Code
CPUSkinning - 01 - Loader.zip (7.18 mb)