Pre-draw estimation requires the archer to make an estimate of target distance before the bow is drawn. For distances of about 30 meters or less the human eye will do quite well with practice. For distances greater than this, the archer can use a little assistance. You can bet a bullseye they are using a framing method to help them get a good idea of the target distance. Since target sizes are still of uniform size, this framing type of range estimation will work quite well.
Some methods follow.
The limb tips of your bow can be used as a framing reference. For instance, a target of known size will appear to be larger at closer distance and smaller at longer distance in relation to the size of your limb tip. Also, you can frame the target between the wheel of the compound bow and the limb tip to get a reference of distance. You can use your sight adjustment knob or virtually any specific sized part of your bow or sight for this framing method. Some archers also hold their arm fully extended as if pointing at the target.