threshold=0, transparent pixel (alpha=0):
false
threshold=0, opaque pixel (alpha=0xFF):
true
threshold=0, out-of-bounds point:
false
threshold=0xA0, pixel alpha=0xA0 (boundary):
true
threshold=0xA1, pixel alpha=0xA0 (just below):
false
threshold=0x9F, pixel alpha=0xA0 (just above):
true
bmd-vs-bmd threshold=0, both transparent:
true
bmd-vs-bmd threshold=0, both opaque:
true
bmd-vs-bmd threshold=0, src opaque / test transparent:
true
