Game variations

A game of Go on a phyiscal board is a linear sequence of moves. Go computer programs such as this app allow to add variations to the main line of moves, in order to explore alternate sequences of moves that in some way differ from the main line.

This manual page introduces the concept of a “game tree” to organize game variations, presents a glossary with term definitions that are important to understand the game tree concept, and then shows with numerous illustrations how the app’s tree view feature works in detail.

The app organizes a game and its variations into a game tree. A game that consists of only the main line is rendered like this:

A game that consists of the main line and several variations is rendered like this:

The following table defines terms that are important to understand because they are used throughout the remainder of this page without any further explanation.

The table is sorted alphabetically to facilitate the lookup of terms. The table is not intended to be read top-down - if you are new the recommended starting point is the term → Node. From there you can follow the cross-references indicated by an arrow (→).

The “Example(s)” column in the table refers to the annotations from the following illustration of a hypothetical game tree.

The app renders the game tree in a tree view which is always located below the game board. In previous illustrations on this page you may have already noticed some of the basic characteristics of the view:

• The game tree is rendered lying on the side.
• The root node is in the top-left corner.
• The main variation is at the top.

In addition, the basic interactons are:

• If the game tree takes up more space than is available you can use the usual swipe gesture to scroll the tree view content in all directions.
• Also if the game tree elements are rendered too small you can use the usual pinch/zoom gestures to zoom in and out. A double-tap gesture zooms in on the board by 50%.

The tree view shares the available vertical space with the game board and possibly some other views. Just above the tree view there is a small translucent bar (outlined in the illustraton with a red rectangle) that you can tap and drag up or down to resize the tree view.

If you do not need the tree view at all you can turn it off in the Settings user interface area under “Tree view > Display tree view”.

Resize animation - tap to expand ↕

The tree view draws lines between nodes to indicate how the nodes are connected. The first child node is always drawn on the same row as its parent node and the two are connected by a horizontal line.

If a node has several child nodes it becomes a branching node where two or more game variations originate. The second, third, etc. child node are connected to their parent node with a non-horizontal branching line. In the Settings user interface area under “Tree view > Branching style” you can select between two styles how the tree view should render branching lines.

This is how the diagonal branching style looks like. It is the default style because it results in a compact rendering of the game tree with as few rows as possible.

This is how the right-angle branching style looks like.

The illustraton shows exactly the same game tree as the previous illustraton for the diagonal branching style.

The advantage of this style is that if there are many branches close to each other it can result in a game tree that is more easily readable. The drawback is that the game tree can take up a lot more vertical space than the diagonal branching style.

The tree view by default renders the game tree in a tabular fashion:

• Rows are filled with game variations.
• Columns are filled with the nodes of the game tree.

This tabular display is possible because all nodes take up the same horizontal and vertical space. The Condense moves section further down on this page illustrates a setting which, when enabled, causes a non-tabular display.

As can be seen in the next illustration, the tree view displays a header with numbers at the top. This is used to number the nodes in the game tree, indicating their distance from the root node. The root node therefore has node number 0 (zero).

As long as the game tree is shown in its default tabular fashion, the node number can also be understood as the table column number.

In a game tree where all nodes contain a move, the node number and the move number are the same.

The header with node numbers remains visible at all times, even when you scroll the tree view downwards.

At any given time one of the variations in the game tree is selected, and one of the nodes within that game variation is selected. The tree view uses the color red to indicate the current selection:

• It marks the currently selected game variation with a red path going through all the lines that connect the variation’s nodes.
• It marks the currently selected node with a red outline.
• It renders the node number of the current node in red color.

In the Settings user interface area under “Tree view > Node selecton style” you can select between three styles how the tree view should render the selected node. The default style is “Light & circular”.

You can tap on a node to make it the currently selected node. If the currently selected game variation does not contain the newly selected node, then the first game variation that contains the node becomes the currently selected game variation.

Nodes are rendered with a symbol that indicates what the node contains. The basic content rules are:

• Setup and moves are the main node content. When present their symbol takes precedence over the symbol of other content.
• Setup and moves are mutually exclusive. A node may contain one or the other, but not both.
• Setup can be present in nodes beyond the root node, but not after the first move.
• The root node may contain setup, but no move.
• Annotations and markup can be present in all nodes, either on their own or in addition to other content.

The following table documents all the possible symbols and their meanings.

Symbol	Description
	A root node that contains a komi value greater than zero. The node does not contain setup, annotations or markup.
	A root node that contains a handicap value greater than zero. The node does not contain setup, annotations or markup.
	A root node that contains both a handicap and a komi value greater than zero. The node does not contain setup, annotations or markup.
	A plain root node without handicap, komi or any other content.
	A node that contains a black move. In addition the node may contain annotations and/or markup, but no setup.
	A node that contains a white move. In addition the node may contain annotations and/or markup, but no setup.
	A node that contains annotations. The node does not contain a move, setup or markup.
	A node that contains markup. The node does not contain a move, setup or annotations.
	A node that contains both annotations and markup. The node does not contain a move or setup.
	A node that contains black setup stones. In addition the node may contain annotations and/or markup, but no move.
	A node that contains white setup stones. In addition the node may contain annotations and/or markup, but no move.
	A node that clears setup stones from a previous node. In addition the node may contain annotations and/or markup, but no move.
	A node that contains black and white setup stones. In addition the node may contain annotations and/or markup, but no move.
	A node that contains black setup stones and also clears setup stones from a previous node. In addition the node may contain annotations and/or markup, but no move.
	A node that contains white setup stones and also clears setup stones from a previous node. In addition the node may contain annotations and/or markup, but no move.
	A node that contains black and white setup stones and also clears setup stones from a previous node. In addition the node may contain annotations and/or markup, but no move.

The app currently does not support creating the following nodes:

• A node that contains only annotations and/or markup but no move.
• A node beyond the root node that contains setup. Board setup is restricted to the root node.

Such nodes can exist, though, when you load SGF files from the archive that were created by other programs.

When a new game begins and you start playing moves, then those moves are simply added one after the other, forming the linear sequence of moves known as the main line, or main game variation.

If you do not want to play with game variations you can turn the feature off in the Settings user interface area under “Game variations > Move creates new game variation when future nodes exist”.

When the setting is disabled the app instead discards future nodes in the current game variation and replaces them with the new move.

By default the tree view draws nodes one after the other as they appear in their game variations. If the game tree contains nodes without moves, then the tree view may draw nodes with moves that have the same move number in different horizontal positons.

This can be changed in the Settings user interface area under “Tree view > Align moves”. When you turn this option on then nodes with moves that have the same move number are drawn in the same horizontal positon.

This illustration shows that the node with move number 1 in different game variations is drawn in different positions:

• Main variation: The node with move number 1 has node number 10.
• Variation 2: The node with move number 1 has node number 3.
• Variation 3: The node with move number 1 has node number 7.

When the “Align moves” setting is enabled, all 3 nodes with move number 1 are aligned on the same horizontal position.

The drawback of aligning moves is that the game tree can take up a lot more horizontal space.

When move nodes are aligned their node number within the game variation does not change. The consequence is that when the “Align moves” setting is enabled node numbering takes place only for the current game variation.

The following illustration shows that in game variation 2 the node with move number 1 still has node number 3 (compare to original illustration without move alignment).

By default the tree view displays all nodes with the same size. This can be changed in the Settings user interface area under “Tree view > Condense moves”. When this setting is turned on, move nodes within a sequence of move nodes are condensed, i.e. they are drawn smaller than move nodes at the beginning or end of the sequence.

The purpose of condensing move nodes is to de-emphasize repetitive content and to enable focusing on interesting nodes in the game tree. This is done at the cost of making the tree look less uniform.

The second illustration shows that certain move nodes are drawn with full size even though they are not at the beginning or end of a sequence of move nodes. These are the exceptions:

• A move node that is a branching node (node number 4 in the illustration). Such a node is considered interesting because it marks a turning point in the game where different decisions lead to different game play.
• A move node that is the beginning of a new branch (node number 5 in three variations). Similarly to branching nodes, such nodes are interesting because they contain the actual move that differs from other branches.
• A move node that is the leaf node of a game variation. These nodes are interesting because they contain the result of playing out the game variation.

When move nodes are condensed the horizontal positioning of nodes can greatly vary and it is no longer possible to uniformly number nodes across all game variations in a tabular fashion. The consequence is that when the “Condense moves” setting is enabled node numbering takes place only for the current game variation.

In addition, the node number of a condensed move node takes up more space than the node it is numbering. This becomes more evident when node numbers have 2, 3 or even 4 digits. Because of this there are gaps in numbering consecutive condensed move nodes, as can be seen above in the second illustration.

One way to change the selected node is to tap on that node in the tree view. However, there are also other triggers outside the tree view that can change the selected node. Examples are when you or the computer play a new move, or when you go to the start or end of the current game variation via one of the navigation buttons (see page The current game variation).

By default when the selected node changes the tree view scrolls to make the newly selected node visible. This behaviour can be changed in the Settings user interface area under “Tree view > Focus on selected node”.

You can either disable focusing on the selected node entirely, or select between three focusing modes.