private void generateStar(IEntityManager entityStore, Game game, Texture2D bigStarTex, Texture2D littleStarTex, Frustum generationVolume, double speedAtUnitDepth, double screenDepth, double screenWidth, double screenHeight)
{
//sample a 3d location for the star
Vector3 starLoc = generationVolume.samplePoint(rand);
//determine the speed as a function of the depth
double speed = speedAtUnitDepth / starLoc.Z * screenDepth * screenDepth;
//determine the depth/speed of the star
Entity star = new Entity();
//Component: Has a position, determined by starLoc
PositionComponent pos = new PositionComponent();
Vector3 starLoc2 = generationVolume.TransformFromEuclideanSpaceToPseudoSphericalSpace(starLoc);
pos.Position = new Vector2(starLoc2.X * game.GraphicsDevice.Viewport.Width, starLoc2.Y * game.GraphicsDevice.Viewport.Height);
star.AddComponent(pos);
//Component: Moves at a constant speed
LinearMovementComponent movementStrat = new LinearMovementComponent();
star.AddComponent(movementStrat);
//Component: Has a move speed
MoveSpeedComponent speedComponent = new MoveSpeedComponent();
speedComponent.MoveSpeed = (float)speed;
star.AddComponent(speedComponent);
//Component: Wraps around the screen
ScreenWrappingComponent wrapper = new ScreenWrappingComponent();
star.AddComponent(wrapper);
//Component: Has a texture. This should be little star for far away/slow stars, big otherwise
TextureComponent tex = new TextureComponent();
tex.Texture = (speed > -2.5) ? littleStarTex : bigStarTex;
tex.SourceRect = tex.Texture.Bounds;
star.AddComponent(tex);
//Component: Has a bounding box
AABBComponent aabb = new AABBComponent();
aabb.Width = tex.Texture.Width;
aabb.Height = tex.Texture.Height;
star.AddComponent(aabb);
//Component: Is rendered at a specific layer (just above the background)
RenderLayerComponent layer = new RenderLayerComponent();
layer.LayerID = 1;
star.AddComponent(layer);
entityStore.Add(star);
}
private void initializeBackgroundStars(IEntityManager entityStore, Game game)
{
Texture2D bigStarTex = game.Content.Load<Texture2D>("spaceArt/png/Background/starBig");
Texture2D littleStarTex = game.Content.Load<Texture2D>("spaceArt/png/Background/starSmall");
//shoot for 1 star per 100000 square pixels
double targetDensity = 0.00007;
int numStars = 0;
double area = game.GraphicsDevice.Viewport.Width * game.GraphicsDevice.Viewport.Height;
double screenWidth = 14; //inches width of my laptop screen
double screenHeight = screenWidth * 9 / 16; //screen height, in same units as above, for a widescreen display
double screenDepth = 20; //approx distance in inches to laptop screen
double maxDepth = 12 * 8; //eight feet away in inches
double speedAtUnitDepth = -4 / screenDepth; //in pixels per frame
Frustum generationVolume = new Frustum(screenWidth, screenHeight, screenDepth, maxDepth);
while (numStars / area < targetDensity)
{
generateStar(entityStore, game, bigStarTex, littleStarTex, generationVolume, speedAtUnitDepth, screenDepth, screenWidth, screenHeight);
numStars++;
}
}
