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diff --git a/Documentation/technical/api-history-graph.txt b/Documentation/technical/api-history-graph.txt new file mode 100644 index 0000000000..ce1c08ee86 --- /dev/null +++ b/Documentation/technical/api-history-graph.txt @@ -0,0 +1,179 @@ +history graph API +================= + +The graph API is used to draw a text-based representation of the commit +history. The API generates the graph in a line-by-line fashion. + +Functions +--------- + +Core functions: + +* `graph_init()` creates a new `struct git_graph` + +* `graph_release()` destroys a `struct git_graph`, and frees the memory + associated with it. + +* `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()` until it returns 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. This should not be called if the commit line has + already been printed, or it will loop forever. + +* `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. + +Data structure +-------------- +`struct git_graph` is an opaque data type used to store the current graph +state. + +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(); + +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); + } +} + +graph_release(graph); +------------ + +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. + +------------ +* +* +M +|\ +* | +| | * +| \ \ +| \ \ +M-. \ \ +|\ \ \ \ +| | * | | +| | | | | * +| | | | | * +| | | | | M +| | | | | |\ +| | | | | | * +| * | | | | | +| | | | | M \ +| | | | | |\ | +| | | | * | | | +| | | | * | | | +* | | | | | | | +| |/ / / / / / +|/| / / / / / +* | | | | | | +|/ / / / / / +* | | | | | +| | | | | * +| | | | |/ +| | | | * +------------ |