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