I'll be totally open with my stuff, I don't think there's much point in just sharing the source as a lot of things I've done will seem opaque.
Basically the physics loop runs 500 times a second, if it only runs as often as the draw (60 times a second) then collisions aren't accurate enough.
I have a ball class, a piston class, a line class, a goal class and a fail class. I check for collisions between the ball and everything else using simple geometry, collision checking for circles is easy. The collision response is slightly more tricky, but it just boils down to newtonian physics, it depends on the frictional coefficient, restitutional coefficient, mass, moment of inertia.
Here is a snippet to show a collision between a line and a ball.
Code:
Vector2 contactPointVelocity = ball.velocity + ball.radius * parallelVector * ball.angularVelocity;
float contactPointVelocityParallel = Vector2.Dot(contactPointVelocity, parallelVector);
float contactPointVelocityNormal = Vector2.Dot(contactPointVelocity, normalVector);
float impulseNormal = ball.mass * -(1 + line.coefficientOfRestitution) * contactPointVelocityNormal;
float impulseRequiredParallel = -contactPointVelocityParallel / (1 / (ball.mass) + ball.radius * ball.radius / ball.momentOfIntertia);
float impulseParallel;
if (Math.Abs(impulseRequiredParallel) <= line.coefficientOfFriction * impulseNormal)
{
impulseParallel = impulseRequiredParallel;
}
else
{
impulseParallel = Math.Sign(impulseRequiredParallel) * line.coefficientOfFriction * impulseNormal;
}
ball.velocity += impulseNormal * normalVector / ball.mass;
ball.velocity += impulseParallel * parallelVector / ball.mass;
ball.angularVelocity += impulseParallel * ball.radius / ball.momentOfIntertia;
ball.position -= ((ball.position - ball.radius * normalVector) - intersectionPoint);
Very easy, the sprite drawing method looks like this (there are different overloaded ones).
Code:
public void Draw(Texture2D texture, Vector2 position, Rectangle? sourceRectangle, Color color, float rotation, Vector2 origin, float scale, SpriteEffects effects, float layerDepth);
The first variable is the texture you want to draw,
the second specifies the position you want to draw it,
the third asks which part of the texture you want to draw, if you want to draw the whole texture just put "null"
the fourth is the colour, if you want to draw it normally put "Color.White"
the fifth is the rotation in radians
the sixth is where you want the origin of the sprite to be, for example my ball sprite is a 40*40 texture, so I put "new Vector2(20, 20)" for the origin, this will draw the centre of the ball at the position I specified, and rotate around the centre of the ball.
the seventh is spriteeffects, this is if you want to flip the sprite, seems useless so I always put SpriteEffects.None
the eighth is the scale, if I wanted a half size ball put 0.5f, you can also put a Vector2 in here to scale differently horizontally and vertically
the last overload is the layerDepth, depends how far forward you want the sprite to be, and how your spriteBatch is set to draw the sprites
