/* Returns true if the two specified entities are colliding. This
* method has pixel-level accuracy.
*/
private static bool CheckCollision(SolidEntity entity1, SolidEntity entity2)
{
/* Immediately grab a reference to each particle sprite image
* (Surface), so that any sprite animation will not trip us up by
* changing surfaces under us.
*/
Surface surface1 = entity1.Sprite.Surface;
Surface surface2 = entity2.Sprite.Surface;
// Find the position of each particle image.
Point surface1Position = new Point(Convert.ToInt32(Math.Truncate(entity1.X)), Convert.ToInt32(Math.Truncate(entity1.Y)));
Point surface2Position = new Point(Convert.ToInt32(Math.Truncate(entity2.X)), Convert.ToInt32(Math.Truncate(entity2.Y)));
// Find the size of each particle image.
Size surface1Size = new Size(Convert.ToInt32(Math.Truncate(entity1.Width)), Convert.ToInt32(Math.Truncate(entity1.Height)));
Size surface2Size = new Size(Convert.ToInt32(Math.Truncate(entity2.Width)), Convert.ToInt32(Math.Truncate(entity2.Height)));
// Put 'em together to make rectangles.
Rectangle surface1Rec = new Rectangle(surface1Position, surface1Size);
Rectangle surface2Rec = new Rectangle(surface2Position, surface2Size);
if (!surface1Rec.IntersectsWith(surface2Rec))
/* The two entity's bounding rectangles don't even intersect.
* They obviously aren't colliding.
*/
// False: entity1 and entity2 are not colliding.
return false;
/* Their rectangles do intersect, so now we need to check each
* pixel in the overlapping area.
*/
// Find the intersecting rectangle of the two entities.
Rectangle intersectingRectangle = new Rectangle(surface1Rec.Location, surface1Rec.Size);
intersectingRectangle.Intersect(surface2Rec);
Point surface1PixelPosition = new Point();
Point surface2PixelPosition = new Point();
/* Lock the two entity's surfaces into memory to allow direct
* pixel manipulation with high performance.
*/
surface1.Lock();
surface2.Lock();
// Check each overlapping pixel.
for (int x = 0; x < intersectingRectangle.Width; x++)
for (int y = 0; y < intersectingRectangle.Height; y++)
{
/* Get the position within each surface of the overlapping
* pixel.
*/
surface1PixelPosition.X = intersectingRectangle.X - surface1Rec.X + x;
surface1PixelPosition.Y = intersectingRectangle.Y - surface1Rec.Y + y;
surface2PixelPosition.X = intersectingRectangle.X - surface2Rec.X + x;
surface2PixelPosition.Y = intersectingRectangle.Y - surface2Rec.Y + y;
/* Get the color from each surface at the overlapping
* pixel. Unlike the GetPixel and SetPixel operations of
* the .NET Image class, the GetPixel and SetPixel
* operations of the C# SDL Surface class allow direct
* pixel manipulation, and do not create their own locks
* (hence the locks happen outside the loop).
*/
Color surface1PixelColor = surface1.GetPixel(surface1PixelPosition);
Color surface2PixelColor = surface2.GetPixel(surface2PixelPosition);
/* True if the pixel at the overlapping point in the
* associated surface is transparent.
*/
bool surface1PixelIsTransparent = surface1.Transparent && surface1PixelColor == surface1.TransparentColor;
bool surface2PixelIsTransparent = surface2.Transparent && surface2PixelColor == surface2.TransparentColor;
/* If both pixels are non-transparent, then we have a
* Collision!
*/
if (!surface1PixelIsTransparent && !surface2PixelIsTransparent)
{
// Unlock the two surfaces before returning.
surface1.Unlock();
surface2.Unlock();
// True: entity1 and entity2 are colliding.
return true;
}
}
// Unlock the two surfaces before returning.
surface1.Unlock();
surface2.Unlock();
// False: entity1 and entity2 are not colliding.
return false;
}
/// <summary>
/// Find the distance between two SolidEntity objects.
/// </summary>
/// <param name="entity1">The first entity.</param>
/// <param name="entity2">The second entity.</param>
/// <returns>
/// The distance (in pixels) between the centers of the two objects.
/// </returns>
public static double GetDistance(SolidEntity entity1, SolidEntity entity2)
{
// Create a vector between the two entities to find the distance.
Vector v = new Vector(entity1.Center, entity2.Center);
return v.Length;
}
/// <summary>
/// Detect a collision between this entity and another.
/// </summary>
/// <param name="otherSolidEntity">
/// The other entity to check for collision with this one.
/// </param>
/// <returns>
/// True if the entities are colliding; false otherwise.
/// </returns>
public bool Collision(SolidEntity otherSolidEntity)
{
if (!this.Alive)
// Dead entities don't collide, because they don't exist.
return false;
bool collisionStatus = SolidEntity.CheckCollision(this, otherSolidEntity);
bool alreadyCollided = this.currentCollisions.Contains(otherSolidEntity);
if (!collisionStatus)
{
// No Collision detected with the other object.
if (alreadyCollided)
/* Last we checked, we were in a Collision with this other
* object, so lets update our Collision list to reflect the
* fact that we are no-longer colliding with it.
*/
this.currentCollisions.Remove(otherSolidEntity);
return false;
}
// Collision detected
if (!alreadyCollided)
{
// A brand new Collision!
this.currentCollisions.Add(otherSolidEntity);
return true;
}
/* A previous Collision with this other object hasn't ended
* yet.
*/
if (this.currentCollisions[this.currentCollisions.Count - 1] == otherSolidEntity)
{
/* This was the exact last object we collided with (in our
* list of currently occurring collisions), so we treat
* this like it never happened. You saw nothing!
*/
return false;
}
else
{
/* Update the list to reflect that we last collided with this
* object. In other words, move it to the back of the list.
*/
this.currentCollisions.Remove(otherSolidEntity);
this.currentCollisions.Add(otherSolidEntity);
return true;
}
}
/// <summary>
/// Find the angle between two SolidEntity objects.
/// </summary>
/// <param name="entity1">The first (origin) entity.</param>
/// <param name="entity2">The second (destination) entity.</param>
/// <returns>
/// The degree of the angle between the centers of the two entities
/// (with entity1's center as the origin).
/// </returns>
public static int GetDirectionDeg(SolidEntity entity1, SolidEntity entity2)
{
// Create a vector between the two entities to find the angle.
Vector v = new Vector(entity1.Center, entity2.Center);
return Convert.ToInt32(Math.Truncate(v.DirectionDeg));
}
