XNA - 3D模型的碰撞檢測 - Part 2

XNA - 3D模型的碰撞檢測 - Part 2
…
例如：

if (bulletBoundingSphere.Intersects(planeBoundingSphere))
{
    //plane's been hit. cue smoke, flames, snakes in a panic, singing nuns, whatever...
}

…
這裡範例展示要如何取得Model的BoundingSphere…

//Load the model using my game's instance of a ContentManager.

Model myModel = MyGame.ContentManager.Load("ContentMeshesMyModel");

foreach (ModelMesh mesh in myModel.Meshes)
{
    //Do stuff with mesh.BoundingSphere
}

…
接著來看看這些程式碼，它們可以在MyGame.cs裡面找到…

private void AnalyseModel()
{
    // Take a copy of the Model's BoneTransforms (transforms to be applied to each part of the model)
    GetBoneTransforms();

    // Build BoundingParts for Collision Detection
    BuildBoundingParts();
}

private void GetBoneTransforms()
{
    _modelBoneTransforms = new Matrix[_model.Bones.Count];
    _model.CopyAbsoluteBoneTransformsTo(_modelBoneTransforms);
}

…
是的，這一切聽起來令人興奮，所以來看看著個好東西。這些程式碼在MyGame.cs約頂部的地方，你可以看到以下有趣的程式碼…

//Blob mesh
private string[] _modelBoundingPartNames = new string[]
{
    "Fuselage",
    "Wing",
    "Tail"
};

private Color[] _modelBoundingPartColours = new Color[]
{  
    Color.Blue,
    Color.Red,
    Color.GreenYellow
};

private Vector4[][] _modelBoundingPartSubdivisions = new Vector4[][]
{
    //Fuselage
    new Vector4[] { new Vector4(0.50f, 0.10f, 0.46f, 0.20f),
                           new Vector4(0.50f, 0.30f, 0.46f, 0.27f),
                           new Vector4(0.50f, 0.60f, 0.48f, 0.26f)
    },
    //Wing
    new Vector4[] { new Vector4(0.07f, 0.51f, 0.50f, 0.20f),
                           new Vector4(0.30f, 0.515f, 0.50f, 0.25f),
                           new Vector4(0.50f, 0.515f, 0.50f, 0.27f),
                           new Vector4(0.70f, 0.515f, 0.50f, 0.25f),
                           new Vector4(0.93f, 0.51f, 0.50f, 0.20f)
    },
    //Tail
    new Vector4[] { new Vector4(0.25f, 0.52f, 0.45f, 0.40f),
                           new Vector4(0.50f, 0.56f, 0.53f, 0.55f),
                           new Vector4(0.75f, 0.52f, 0.45f, 0.40f)
    }
};

…
接下來看BuildBoundingParts()方法會做些甚麼事情！

/// 

/// Builds a collection of BoundingParts for each ModelMesh in the Model.
/// Each BoundingPart will contain one or many BoundingSphere as defined in the _modelBoundingPartSubdivisions array.
/// 
private void BuildBoundingParts()
{
   _modelBoundingParts = new BoundingPartList();

   BoundingPart boundingPart;

   int meshIndex = 0;
   foreach (ModelMesh mesh in _model.Meshes)
   {
       BoundingSphere[] pieces = new BoundingSphere[_modelBoundingPartSubdivisions[meshIndex].Length];
       int pieceIndex = 0;

       //Create, Scale and Position new BoundingSphere's according to the defined subdivisions for this part of the model.
       foreach (Vector4 subdivision in _modelBoundingPartSubdivisions[meshIndex])
       {
           //Determine the new BoundingSphere's Radius
           float radius = subdivision.W * mesh.BoundingSphere.Radius;

           //Determine the new BoundingSphere's Center by interpolating.
           //The subdivision's X, Y, Z represent percentages in each axis.  They will used across the full diameter of XNA's "default" BoundingSphere.
           float x = MathHelper.Lerp(mesh.BoundingSphere.Center.X - mesh.BoundingSphere.Radius, mesh.BoundingSphere.Center.X + mesh.BoundingSphere.Radius, subdivision.X);
           float y = MathHelper.Lerp(mesh.BoundingSphere.Center.Y - mesh.BoundingSphere.Radius, mesh.BoundingSphere.Center.Y + mesh.BoundingSphere.Radius, subdivision.Y);
           float z = MathHelper.Lerp(mesh.BoundingSphere.Center.Z - mesh.BoundingSphere.Radius, mesh.BoundingSphere.Center.Z + mesh.BoundingSphere.Radius, subdivision.Z);
           Vector3 centre = new Vector3(x, y, z);

           pieces[pieceIndex] = new BoundingSphere(centre, radius);

           pieceIndex++;
       }
       boundingPart = new BoundingPart(mesh.BoundingSphere, pieces, _modelBoneTransforms[mesh.ParentBone.Index], _modelBoundingPartNames[meshIndex], _modelBoundingPartColours[meshIndex]);

       _modelBoundingParts.Add(boundingPart);
       meshIndex++;
   }
}