Documentation/technical/api-history-graph.txt

   1 history graph API
   2 =================
   3
   4 The graph API is used to draw a text-based representation of the commit
   5 history.  The API generates the graph in a line-by-line fashion.
   6
   7 Functions
   8 ---------
   9
  10 Core functions:
  11
  12 * `graph_init()` creates a new `struct git_graph`
  13
  14 * `graph_release()` destroys a `struct git_graph`, and frees the memory
  15   associated with it.
  16
  17 * `graph_update()` moves the graph to a new commit.
  18
  19 * `graph_next_line()` outputs the next line of the graph into a strbuf.  It
  20   does not add a terminating newline.
  21
  22 * `graph_padding_line()` outputs a line of vertical padding in the graph.  It
  23   is similar to `graph_next_line()`, but is guaranteed to never print the line
  24   containing the current commit.  Where `graph_next_line()` would print the
  25   commit line next, `graph_padding_line()` prints a line that simply extends
  26   all branch lines downwards one row, leaving their positions unchanged.
  27
  28 * `graph_is_commit_finished()` determines if the graph has output all lines
  29   necessary for the current commit.  If `graph_update()` is called before all
  30   lines for the current commit have been printed, the next call to
  31   `graph_next_line()` will output an ellipsis, to indicate that a portion of
  32   the graph was omitted.
  33
  34 The following utility functions are wrappers around `graph_next_line()` and
  35 `graph_is_commit_finished()`.  They always print the output to stdout.
  36 They can all be called with a NULL graph argument, in which case no graph
  37 output will be printed.
  38
  39 * `graph_show_commit()` calls `graph_next_line()` until it returns non-zero.
  40   This prints all graph lines up to, and including, the line containing this
  41   commit.  Output is printed to stdout.  The last line printed does not contain
  42   a terminating newline.  This should not be called if the commit line has
  43   already been printed, or it will loop forever.
  44
  45 * `graph_show_oneline()` calls `graph_next_line()` and prints the result to
  46   stdout.  The line printed does not contain a terminating newline.
  47
  48 * `graph_show_padding()` calls `graph_padding_line()` and prints the result to
  49   stdout.  The line printed does not contain a terminating newline.
  50
  51 * `graph_show_remainder()` calls `graph_next_line()` until
  52   `graph_is_commit_finished()` returns non-zero.  Output is printed to stdout.
  53   The last line printed does not contain a terminating newline.  Returns 1 if
  54   output was printed, and 0 if no output was necessary.
  55
  56 * `graph_show_strbuf()` prints the specified strbuf to stdout, prefixing all
  57   lines but the first with a graph line.  The caller is responsible for
  58   ensuring graph output for the first line has already been printed to stdout.
  59   (This can be done with `graph_show_commit()` or `graph_show_oneline()`.)  If
  60   a NULL graph is supplied, the strbuf is printed as-is.
  61
  62 * `graph_show_commit_msg()` is similar to `graph_show_strbuf()`, but it also
  63   prints the remainder of the graph, if more lines are needed after the strbuf
  64   ends.  It is better than directly calling `graph_show_strbuf()` followed by
  65   `graph_show_remainder()` since it properly handles buffers that do not end in
  66   a terminating newline.  The output printed by `graph_show_commit_msg()` will
  67   end in a newline if and only if the strbuf ends in a newline.
  68
  69 Data structure
  70 --------------
  71 `struct git_graph` is an opaque data type used to store the current graph
  72 state.
  73
  74 Calling sequence
  75 ----------------
  76
  77 * Create a `struct git_graph` by calling `graph_init()`.  When using the
  78   revision walking API, this is done automatically by `setup_revisions()` if
  79   the '--graph' option is supplied.
  80
  81 * Use the revision walking API to walk through a group of contiguous commits.
  82   The `get_revision()` function automatically calls `graph_update()` each time
  83   it is invoked.
  84
  85 * For each commit, call `graph_next_line()` repeatedly, until
  86   `graph_is_commit_finished()` returns non-zero.  Each call go
  87   `graph_next_line()` will output a single line of the graph.  The resulting
  88   lines will not contain any newlines.  `graph_next_line()` returns 1 if the
  89   resulting line contains the current commit, or 0 if this is merely a line
  90   needed to adjust the graph before or after the current commit.  This return
  91   value can be used to determine where to print the commit summary information
  92   alongside the graph output.
  93
  94 Limitations
  95 -----------
  96
  97 * `graph_update()` must be called with commits in topological order.  It should
  98   not be called on a commit if it has already been invoked with an ancestor of
  99   that commit, or the graph output will be incorrect.
 100
 101 * `graph_update()` must be called on a contiguous group of commits.  If
 102   `graph_update()` is called on a particular commit, it should later be called
 103   on all parents of that commit.  Parents must not be skipped, or the graph
 104   output will appear incorrect.
 105 +
 106 `graph_update()` may be used on a pruned set of commits only if the parent list
 107 has been rewritten so as to include only ancestors from the pruned set.
 108
 109 * The graph API does not currently support reverse commit ordering.  In
 110   order to implement reverse ordering, the graphing API needs an
 111   (efficient) mechanism to find the children of a commit.
 112
 113 Sample usage
 114 ------------
 115
 116 ------------
 117 struct commit *commit;
 118 struct git_graph *graph = graph_init(opts);
 119
 120 while ((commit = get_revision(opts)) != NULL) {
 121         graph_update(graph, commit);
 122         while (!graph_is_commit_finished(graph))
 123         {
 124                 struct strbuf sb;
 125                 int is_commit_line;
 126
 127                 strbuf_init(&sb, 0);
 128                 is_commit_line = graph_next_line(graph, &sb);
 129                 fputs(sb.buf, stdout);
 130
 131                 if (is_commit_line)
 132                         log_tree_commit(opts, commit);
 133                 else
 134                         putchar(opts->diffopt.line_termination);
 135         }
 136 }
 137
 138 graph_release(graph);
 139 ------------
 140
 141 Sample output
 142 -------------
 143
 144 The following is an example of the output from the graph API.  This output does
 145 not include any commit summary information--callers are responsible for
 146 outputting that information, if desired.
 147
 148 ------------
 149 *
 150 *
 151 M
 152 |\
 153 * |
 154 | | *
 155 | \ \
 156 |  \ \
 157 M-. \ \
 158 |\ \ \ \
 159 | | * | |
 160 | | | | | *
 161 | | | | | *
 162 | | | | | M
 163 | | | | | |\
 164 | | | | | | *
 165 | * | | | | |
 166 | | | | | M  \
 167 | | | | | |\  |
 168 | | | | * | | |
 169 | | | | * | | |
 170 * | | | | | | |
 171 | |/ / / / / /
 172 |/| / / / / /
 173 * | | | | | |
 174 |/ / / / / /
 175 * | | | | |
 176 | | | | | *
 177 | | | | |/
 178 | | | | *
 179 ------------