The Porterduff.mode class in Android lists the rules they make:
Android.graphics.PorterDuff.Mode. SRC: Drawing only source images
Android.graphics.PorterDuff.Mode. DST: Draw only the target image
Android.graphics.PorterDuff.Mode. dst_over: Draws the target image at the top of the source image
Android.graphics.PorterDuff.Mode. dst_in: Draws the target image only where the source image and the target image intersect
Android.graphics.PorterDuff.Mode. dst_out: Draws the target image only where the source image and the target image do not intersect
Android.graphics.PorterDuff.Mode. dst_atop: Draws the target image where the source and destination images intersect, drawing the source image where it does not intersect
Android.graphics.PorterDuff.Mode. src_over: Draws the source image at the top of the target image
Android.graphics.PorterDuff.Mode. src_in: Draws the source image only where the source and destination images intersect
Android.graphics.PorterDuff.Mode. src_out: Draws the source image only where the source and destination images do not intersect
Android.graphics.PorterDuff.Mode. src_atop: Draws the source image where the source and destination images intersect, and draws the target image where it does not intersect
Android.graphics.PorterDuff.Mode. XOR: Draw them anywhere outside of the source image and target image, and do not draw any content where they do not overlap
Android.graphics.PorterDuff.Mode. lighten: Obtains the brightest pixel in two images in each position and displays
Android.graphics.PorterDuff.Mode. Darken: Obtains the darkest pixel of two images in each position and displays
Android.graphics.PorterDuff.Mode. MULTIPLY: Multiplies two pixels per location by 255, and then uses that value to create a new pixel to display. Result color = top Color * Bottom Color/255
Android.graphics.PorterDuff.Mode. screen: Invert each color, perform the same action (multiply them by 255), and then invert again. Result Color =255-(((255-top color) * (255-bottom color))/255)
Android Canvas Sets the processing mode for overlapping portions of painting "with"