Curling

Goal

Two teams take turns sliding eight granite stones toward the house, the painted target at the end of the ice. When the end is over, only the team whose stone is closest to the button (the centre) scores: one point for each stone closer than the best opposing stone. After the last end, the higher total wins; if it is tied, an extra end is played.

How it works

• Only stones touching the house can count. An end where nobody scores is a blank end.
• The team that throws the last stone has the hammer, a big advantage. After an end, it goes to the team that did not score; it is kept after a blank end.
• A stone must completely cross the far hog line, unless it hits a stone already in play; it is removed if it touches a side line or completely crosses the back line.
• Free guard zone: during the first five stones of the end, an opposing stone sitting between the hog line and the tee line, outside the house, cannot be knocked out of play. In case of a violation, the stones are put back and the thrown stone is removed.

Throwing

• Place your skip’s broom by touching the ice (or sliding sideways): this is the aiming line.
• Choose the rotation: a stone thrown with a clockwise rotation curls to the right, with a counterclockwise rotation to the left. The curl increases as the stone slows down.
• Pull back (down, or to the left on a wide screen) to set the power, then release. The gauge shows guard, house or takeout.
• While the stone slides, tap the screen repeatedly (or press the space bar) to sweep: the stone travels farther and curls a little less.
• Keyboard: arrows to move the broom across the sheet and to set the power (pull back: harder), R for the rotation, Enter to throw.

About the AI

The slide is simulated step by step (250 steps per second): friction, rotation-driven curl, near-elastic collisions computed at the exact moment of contact. The AI has an identical engine in a separate worker thread. It generates dozens of shots (draws, freezes, guards, takeouts with a roll, raises), finds the exact speed and angle for each by inverting the trajectory, simulates the full result and evaluates it: counting stones, protection from guards, value of the hammer, score and ends remaining. The best shots are replayed under the execution noise of its level to pick the safest; at the higher levels, it also simulates your best reply at the end of the end. Its final throw carries a weight and angle error that shrinks with the level (almost zero at Master level).