Animation issue caused by C# parameters passed by reference rather than value, but where?
- by Jordan Roher
I'm having trouble with sprite animation in XNA that appears to be caused by a struct passed as a reference value. But I'm not using the ref keyword anywhere. I am, admittedly, a C# noob, so there may be some shallow bonehead error in here, but I can't see it.
I'm creating 10 ants or bees and animating them as they move across the screen. I have an array of animation structs, and each time I create an ant or bee, I send it the animation array value it requires (just [0] or [1] at this time). Deep inside the animation struct is a timer that is used to change frames. The ant/bee class stores the animation struct as a private variable.
What I'm seeing is that each ant or bee uses the same animation struct, the one I thought I was passing in and copying by value. So during Update(), when I advance the animation timer for each ant/bee, the next ant/bee has its animation timer advanced by that small amount. If there's 1 ant on screen, it animates properly. 2 ants, it runs twice as fast, and so on. Obviously, not what I want.
Here's an abridged version of the code. How is BerryPicking's ActorAnimationGroupData[] getting shared between the BerryCreatures?
class BerryPicking
{
private ActorAnimationGroupData[] animations;
private BerryCreature[] creatures;
private Dictionary<string, Texture2D> creatureTextures;
private const int maxCreatures = 5;
public BerryPickingExample()
{
this.creatures = new BerryCreature[maxCreatures];
this.creatureTextures = new Dictionary<string, Texture2D>();
}
public void LoadContent()
{
// Returns data from an XML file
Reader reader = new Reader();
animations = reader.LoadAnimations();
CreateCreatures();
}
// This is called from another function I'm not including because it's not relevant to the problem.
// In it, I remove any creature that passes outside the viewport by setting its creatures[] spot to null.
// Hence the if(creatures[i] == null) test is used to recreate "dead" creatures. Inelegant, I know.
private void CreateCreatures()
{
for (int i = 0; i < creatures.Length; i++)
{
if (creatures[i] == null)
{
// In reality, the name selection is randomized
creatures[i] = new BerryCreature("ant");
// Load content and texture (which I create elsewhere)
creatures[i].LoadContent(
FindAnimation(creatures[i].Name),
creatureTextures[creatures[i].Name]);
}
}
}
private ActorAnimationGroupData FindAnimation(string animationName)
{
int yourAnimation = -1;
for (int i = 0; i < animations.Length; i++)
{
if (animations[i].name == animationName)
{
yourAnimation = i;
break;
}
}
return animations[yourAnimation];
}
public void Update(GameTime gameTime)
{
for (int i = 0; i < creatures.Length; i++)
{
creatures[i].Update(gameTime);
}
}
}
class Reader
{
public ActorAnimationGroupData[] LoadAnimations()
{
ActorAnimationGroupData[] animationGroup;
XmlReader file = new XmlTextReader(filename);
// Do loading...
// Then later
file.Close();
return animationGroup;
}
}
class BerryCreature
{
private ActorAnimation animation;
private string name;
public BerryCreature(string name)
{
this.name = name;
}
public void LoadContent(ActorAnimationGroupData animationData, Texture2D sprite)
{
animation = new ActorAnimation(animationData);
animation.LoadContent(sprite);
}
public void Update(GameTime gameTime)
{
animation.Update(gameTime);
}
}
class ActorAnimation
{
private ActorAnimationGroupData animation;
public ActorAnimation(ActorAnimationGroupData animation)
{
this.animation = animation;
}
public void LoadContent(Texture2D sprite)
{
this.sprite = sprite;
}
public void Update(GameTime gameTime)
{
animation.Update(gameTime);
}
}
struct ActorAnimationGroupData
{
// There are lots of other members of this struct, but the timer is the only one I'm worried about.
// TimerData is another struct
private TimerData timer;
public ActorAnimationGroupData()
{
timer = new TimerData(2);
}
public void Update(GameTime gameTime)
{
timer.Update(gameTime);
}
}
struct TimerData
{
public float currentTime;
public float maxTime;
public TimerData(float maxTime)
{
this.currentTime = 0;
this.maxTime = maxTime;
}
public void Update(GameTime gameTime)
{
currentTime += (float)gameTime.ElapsedGameTime.TotalSeconds;
if (currentTime >= maxTime)
{
currentTime = maxTime;
}
}
}
