Read Me: BoingX

This is just a simple little demo that shows off 

using Quartz Extreme to provide borderless OpenGL 

content on the desktop. It was inspired by the 

Boing demo for the Amiga personal computer.  While 

the original demo used color cycling and the 

Amiga's dual playfield hardware for moving the 

ball around, this demo uses an actual 3D object 

with real lighting. Unlike the original, this 

one doesn't include sound.

When the app starts up the ball is just bouncing 

around inside the window.  Hitting the 's' key 

resizes the window to 2X normal size.   Hitting 'm' 

will enable multisampling if a multisample pixel 

format was available.  Hitting 'l' enables lighting 

for that added "ooh aah" effect.   The final magic 

demo key is to hit 't' which makes the background 

fade away and the ball then starts to bounce 

around on your desktop.

The code is fairly straightforward, and uses the 

NSOpenGLCPSurfaceOpacity parameter to mark the 

view as being transparent. Note that the background 

is always marked as being non-opaque, it's just that 

the background is drawn with opaque colors until the 

background fades out.   The other interesting tidbit 

is the use of 

glBlendFunc(GL_SRC_ALPHA_SATURATE, GL_ONE_MINUS_SRC_ALPHA) 

for doing the ball shadow.   Using GL_SRC_ALPHA would 

unfortunately trash the background alpha and the ball 

shadow would show through to the desktop, which isn't 

what is desired in this case.