history graph API

Functions

Core functions:

graph_init() creates a new struct git_graph
graph_update() moves the graph to a new commit.
graph_next_line() outputs the next line of the graph into a strbuf. It does not add a terminating newline.
graph_padding_line() outputs a line of vertical padding in the graph. It is similar to graph_next_line(), but is guaranteed to never print the line containing the current commit. Where graph_next_line() would print the commit line next, graph_padding_line() prints a line that simply extends all branch lines downwards one row, leaving their positions unchanged.
graph_is_commit_finished() determines if the graph has output all lines necessary for the current commit. If graph_update() is called before all lines for the current commit have been printed, the next call to graph_next_line() will output an ellipsis, to indicate that a portion of the graph was omitted.

The following utility functions are wrappers around graph_next_line() and graph_is_commit_finished(). They always print the output to stdout. They can all be called with a NULL graph argument, in which case no graph output will be printed.

graph_show_commit() calls graph_next_line() and graph_is_commit_finished() until one of them return non-zero. This prints all graph lines up to, and including, the line containing this commit. Output is printed to stdout. The last line printed does not contain a terminating newline.
graph_show_oneline() calls graph_next_line() and prints the result to stdout. The line printed does not contain a terminating newline.
graph_show_padding() calls graph_padding_line() and prints the result to stdout. The line printed does not contain a terminating newline.
graph_show_remainder() calls graph_next_line() until graph_is_commit_finished() returns non-zero. Output is printed to stdout. The last line printed does not contain a terminating newline. Returns 1 if output was printed, and 0 if no output was necessary.
graph_show_strbuf() prints the specified strbuf to stdout, prefixing all lines but the first with a graph line. The caller is responsible for ensuring graph output for the first line has already been printed to stdout. (This can be done with graph_show_commit() or graph_show_oneline().) If a NULL graph is supplied, the strbuf is printed as-is.
graph_show_commit_msg() is similar to graph_show_strbuf(), but it also prints the remainder of the graph, if more lines are needed after the strbuf ends. It is better than directly calling graph_show_strbuf() followed by graph_show_remainder() since it properly handles buffers that do not end in a terminating newline. The output printed by graph_show_commit_msg() will end in a newline if and only if the strbuf ends in a newline.

Calling sequence

Create a struct git_graph by calling graph_init(). When using the revision walking API, this is done automatically by setup_revisions() if the --graph option is supplied.
Use the revision walking API to walk through a group of contiguous commits. The get_revision() function automatically calls graph_update() each time it is invoked.
For each commit, call graph_next_line() repeatedly, until graph_is_commit_finished() returns non-zero. Each call go graph_next_line() will output a single line of the graph. The resulting lines will not contain any newlines. graph_next_line() returns 1 if the resulting line contains the current commit, or 0 if this is merely a line needed to adjust the graph before or after the current commit. This return value can be used to determine where to print the commit summary information alongside the graph output.

Limitations

graph_update() must be called with commits in topological order. It should not be called on a commit if it has already been invoked with an ancestor of that commit, or the graph output will be incorrect.
graph_update() must be called on a contiguous group of commits. If graph_update() is called on a particular commit, it should later be called on all parents of that commit. Parents must not be skipped, or the graph output will appear incorrect.

graph_update() may be used on a pruned set of commits only if the parent list has been rewritten so as to include only ancestors from the pruned set.
The graph API does not currently support reverse commit ordering. In order to implement reverse ordering, the graphing API needs an (efficient) mechanism to find the children of a commit.

Sample usage

struct commit *commit;
struct git_graph *graph = graph_init(opts);

while ((commit = get_revision(opts)) != NULL) {
        graph_update(graph, commit);
        while (!graph_is_commit_finished(graph))
        {
                struct strbuf sb;
                int is_commit_line;

                strbuf_init(&sb, 0);
                is_commit_line = graph_next_line(graph, &sb);
                fputs(sb.buf, stdout);

                if (is_commit_line)
                        log_tree_commit(opts, commit);
                else
                        putchar(opts->diffopt.line_termination);
        }
}

Sample output

The following is an example of the output from the graph API. This output does not include any commit summary information—callers are responsible for outputting that information, if desired.