Part B of this example adds some 3D models and animates them to make the example a little more dramatic.
If you are adding audio to a 2D game, you can just skip this section and go to Part C.
If you are adding audio to a 3D game, you can start the code portion of this exam- ple with either the MGHWinBaseCode project or the MGH360BaseCode project, found in the BaseCode folder on this book’s website.
Loading, Drawing, and Animating the Spacecraft
For this first portion of code, you will load and draw two spaceship models. Ship0 travels with the camera and ship1 moves continuously from side to side off in the dis- tance. All together, the model files consist of the alien0.fbx, alien1.fbx, and spaceA.bmp files. The two .fbx files must be referenced from a Models folder under the Content node in your game project. You can find these files in the Models folder on this book’s website.
Two model objects and matrices for storing their meshes are needed in the game class to store, transform, and draw the model:
Model ship0Model, ship1Model;
Matrix[] ship1Matrix, ship0Matrix;
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You must initialize the spacecraft models and their bone transformation matrices when the game begins. You can add this code to the game class to load and initialize them:
void InitializeModels(){
ship0Model = Content.Load<Model>("Models\\alien0");
ship0Matrix = new Matrix[ship0Model.Bones.Count];
ship0Model.CopyAbsoluteBoneTransformsTo(ship0Matrix);
ship1Model = Content.Load<Model>("Models\\alien1");
ship1Matrix = new Matrix[ship1Model.Bones.Count];
ship1Model.CopyAbsoluteBoneTransformsTo(ship1Matrix);
}
To ensure that the spacecraft models are set up properly when the program begins, add the call statement forInitializeModels()to theInitialize()method in your game class:
InitializeModels();
Ship1 is going to be animated, so it translates back and forth on the X axis. To per- form this animation, you use variables to store ship1’s current position and velocity, and ship1’s direction. These corresponding class-level declarations are needed at the top of your game class:
bool rightDirection = false; // track ship 1
Vector3 ship1Position = new Vector3(0.0f, 0.2f, -BOUNDARY);
Vector3 ship1Velocity = new Vector3(-1.3f, 0.0f, 0.0f);
This next method,UpdateShip1Position(), allows you to update ship1 each frame so it translates side to side in your world along the X axis.
A check is made to determine if ship1 has reached the left or right edge of the world on the X axis. If it reaches the edge of the world, ship1’s direction is reversed and its position is then incremented.
Adding theUpdateShip1Position()method ensures that the position and di- rection of ship1 are updated each frame for a smooth animation:
void UpdateShip1Position(GameTime gameTime){
// reverse direction if pass right boundary
if (ship1Position.X > BOUNDARY && rightDirection == true){
ship1Velocity.X *= -1.0f;
rightDirection = false;
}
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// reverse direction if pass left boundary
else if (ship1Position.X < -BOUNDARY && rightDirection == false){
ship1Velocity.X *= -1.0f;
rightDirection = true;
}
// increment position by time scale so speed is same rate all systems float time = (float)
gameTime.ElapsedGameTime.Milliseconds/200.0f;
ship1Position.X += ship1Velocity.X * time;
}
The code for updating ship1’s angle and position is triggered from theUpdate() method with a call to theUpdateShip1Position()method:
UpdateShip1Position(gameTime);
Next, a method calledWorldMatrix()is needed in the game class to generate transformations for both spaceships:
Matrix WorldMatrix(string modelName){
Matrix rotationY, rotationYOrbit, translation, translationOrbit;
Matrix world = new Matrix();
switch (modelName){
case "ship0":
translation = Matrix.CreateTranslation(
cam.position.X, 0.0f, cam.position.Z);
translationOrbit
= Matrix.CreateTranslation(0.0f, 0.0f, 1.9f);
Vector3 look = cam.view - cam.position;
rotationYOrbit= Matrix.CreateRotationY((float) (Math.Atan2(look.X, look.Z)));
world = translationOrbit * rotationYOrbit * translation;
break;
case "ship1":
translation = Matrix.CreateTranslation(ship1Position);
if (rightDirection)
rotationY = Matrix.CreateRotationY( MathHelper.Pi/2.0f);
else
rotationY = Matrix.CreateRotationY(-MathHelper.Pi/2.0f);
world = rotationY * translation;
break;
}
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return world;
}
The code you add to the game class to draw the spaceships is similar to code you have already seen in this book for drawing models. This time, though, the routine calls theWorldMatrix()method to generate the cumulative transformation:
void DrawModel(Model model, string modelName){
// declare matrices
Matrix world = WorldMatrix(modelName);
foreach (ModelMesh mesh in model.Meshes){
foreach (BasicEffect effect in mesh.Effects) { // pass wvp to shader
switch(modelName) { case "ship0":
effect.World = ship0Matrix[mesh.ParentBone.Index]*world;
break;
case "ship1":
effect.World = ship1Matrix[mesh.ParentBone.Index]*world;
break;
}
effect.View = cam.viewMatrix;
effect.Projection = cam.projectionMatrix;
// set lighting
effect.EnableDefaultLighting();
}
// draw object mesh.Draw();
} }
To draw each spacecraft, you call DrawModel() separately with the correct model and identifier as parameters from theDraw()method:
DrawModel(ship0Model, "ship0");
DrawModel(ship1Model, "ship1");
Since ship0 travels with your camera, you will want to set your view direction so the camera does not bounce up and down. To do this, replace the return statement in- sideChangeView()with this revision:
return new Vector2(change.X, 0.0f);
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When you compile and run the program, you will see ship1 flying from side to side in your 3D world and ship0 will travel with your camera.