So with the recent influx of physics related games, as well as a recent increase in the interest of ball physics, I have become a bit more interested in it myself, and so I spent all of Bio the other day and a considerable amount of time out of class writing this pinball physics engine for pixel based collision.  It uses the onscreen pixels only for collision, although it could easily be changed to a backbuffer or alternative buffer.  This is developed for pinball games in mind, and has several changeable variables which can change the way the ball behaves:

Collision Elasticity: from 0% to 100% How much energy the ball retains after a collision with a wall or object
Rolling Angle Threshold: from 0 to 90 degrees, this value changes how small of an angle the ball has to hit the wall to switch to rolling physics.  If this number is very small, the ball will bound around a lot, if this number is very large, the ball will tend to 'stick' to walls.

These values are currently hardcoded into the code, but in the future I hope to release a flexible engine with a large number of changeable parameters.  As for the engine itself, this is how it works:

The balls position is first backed up, and then incremented by the velocity.  If the ball collides with anything, we enter the collision test segment.  The ball checks the pixels around it to determine the surface normal vector of the wall it collided with.  It then normalizes that vector and uses it to move the ball backwards out of the wall.  If the vector is not accurate enough to get the ball out of the wall, the balls backed up position value is used instead.  We then find the dot product of the balls velocity and the surface normal vector, resulting in a value from -M to M, where M is the magnitude of the velocity of the ball.  If this value is greater than the Rolling angle threshold, perform the vector transformations to subtract the perpendicular vector component from the velocity of the ball.  If the value is less than the Rolling angle threshold, the perpendicular vector is negated, and then multiplied by the Collision Elasticity value.  

Thats a lot of technical mumbo jumbo, lets just get to the screenshots, enjoy!  The screenshot it running with a collision elasticity of 0.5 and a rolling angle threshold of 22.5 degrees

Wow, this looks awesome
Is this the start of a pinball clone by any chance, or is it just a proof of concept?

EDIT 600 posts

And at this rate, it looks like something's going to crop up soon...
If Tio weren't keeping me busy, I would try it in a blink

Builderboy, this is so amazing that I wish you would make your own pinball game

No pressure

What do you mean?

Well, I was hoping for something like a 3D physics engine...

j/k

Looks great!  It's really fun to play with.

As always the physics look awesome.

Don't think there is a download yet graphmastur