Blur Brush

All four work with paint that is already there, moving it around rather than adding color. They share the brush Size, they lock the camera while a stroke is held, and each stroke is one undo step. A smudge that obeys gravity is, as far as I know, unique to MechaPaint. Of course, that only matters if it gets you a convincing drip faster than painting one by hand, and it does.

The four modes

• Blur - Softens the paint under the brush.
• Sharpen - The opposite. Accentuates the detail under the brush.
• Smudge - Drags the color along with the stroke, like a finger through wet paint. Move the brush to pull the color along.
• Streak - A gravity smudge. Hold it and the paint runs downhill in world space, shedding drips that travel well past the brush, wander and die out. Orbit the model and it still runs the same way.

Option bar

• Amount - 0 to 1. How strong the effect is under the brush.
• Falloff - 0 to 1. How softly the effect fades from the brush center to its edge.
• Momentum - 0 to 1, Streak only. How long the paint keeps running after you release the button. The chip is hidden in the other three modes.

Notes on Streak

• Downhill is world down projected to the screen at the surface point, computed once, which is why orbiting leaves it alone.
• Tilt the camera a little off the gravity axis, so downhill has a direction on screen to run in.
• The drips are independent particles spawned under the brush while you hold it, each with its own radius, speed, wander and lifetime. They keep traveling after you release, so a run reaches far past the brush footprint.