Tangram

Goal of the game

The tangram is made of seven pieces cut from a single square: two large triangles, one medium triangle, two small triangles, a square and a parallelogram. Assemble them to cover the dark silhouette exactly: every piece must be used, with no overlap and nothing sticking out.

Controls

• Drag a piece to move it; it lifts under your finger and gently snaps to the right places and to neighbouring corners.
• Tap a piece without moving it to rotate it by an eighth of a turn (45°) clockwise.
• The buttons at the bottom rotate the selected piece one way or the other, flip the parallelogram (the only piece that is not symmetrical) and tidy the loose pieces into the case.
• With a mouse: right-click or scroll wheel to rotate. On the keyboard: Tab selects a piece, arrow keys move it, Q and E rotate it, F flips the parallelogram.

Levels

At Easy level, the outline of the pieces appears faintly and every piece arrives already in the right orientation. After that, the silhouettes become more compact and the snapping more subtle; at Diabolical level, pure geometric shapes give no clue about any piece. Each level offers about ten silhouettes: the collection in the side panel (or the silhouettes button on a phone) lets you pick one and keeps track of your successes.

About the silhouettes

Each silhouette is defined by an exact solution (position and rotation of the seven pieces) whose outline is computed geometrically: it can therefore always be built. Success is detected by the actual coverage of the silhouette, with a small tolerance: any other valid solution is accepted. The hint places one piece in its reference position.