It occurs to me that I completely forgot to write a little howto/tutorial for brush. Here goes.

• Download and unzip the program. Move “brush 0.1″ to your Applications folder. Open brush from there. After a Max/MSP Runtime splash screen, three windows will appear. The Status (or “Max”) window is just for error messages* and we can close it for now.
• Let’s look at the brush window: this is where you control the application. Start the patch metro** by clicking the checkbox next to START PATCH in the bottom left corner. For now, let’s load in a Quicktime movie to make sure that the patch’s basic functions work. Click ‘read’ and select a Quicktime movie, which should start playing in the preview window and the light window.
• You should see trails in the video from the feedback effect. Click and drag the decay slider and notice what happens to the image: if you slide it all the way to the right pixels that are written to the screen will not change (fade) unless they are overwritten by the video. Move the decay slider to the left and image will leave shorter trails and fade more quickly. Now move the tolerance fader back and forth. When it’s all the way to the right, very little feedback happens.
• Clicking the invert checkbox inverts the color information (useful in brightly lit situations).
• If you hit the spacebar, the metro will shut off, halting all processing. I use this like a kill switch so I can, say, grab some light from the exit sign in the corner, kill the patch while I move the camera, then start it again to grab some light off my powercord, skipping all the intervening light in the room. It’s a cheap hack but it works.
• Hit the ESC key or click the checkbox next to “FULLSCREEN” to (surprise, surprise) make the light window fullscreen. You might want to drag the light window to your second monitor first.
• Extra Happy Bonus Fun: Click the “see the guts” button to see where the magic happens.

* You may get an error about jit.gl.shader — I think it’s cause my graphics card can’t do GL_ARB_fragment_program — but there’s no OpenGL in this version of the patch so it doesn’t matter.
** an object that says “do something” thirty times a second. If it isn’t saying that, nothing does anything.