Attributes such as bump, transparency, and incandescence paint as grayscale values—you must do a software render to see their effect. While this is to be expected, there may be times when you want to see the effects of your brush strokes as you paint them. You can do this using IPR.
You can use the 3D Paint Tool while High Quality Rendering is turned on; this enables you to preview attributes such as bump and transparency while painting them, however you cannot see the stroke itself while it is being painted, since the texture is updated only at the end of each stroke.