Visualization of Compiler Graphs

Description

Features

• The VCG tool is not a graph editor. It is intended to visualize large graphs that are automatically generated by programs, e.g. debuggers of data structures.
• Speed is always the first priority. Examples:

     Type  | nodes | edges | Time     |  Mode   
     ----------------------------------------------
     tree  | 4095  | 4094  |   2 sec. | normal
     graph |   66  |   95  |   3 sec. | normal
     graph |  132  |  288  |   5 sec. | normal
     graph |   20  |  190  |  14 sec. | normal
     graph |   26  |  325  |  22 sec. | normal
     graph |   75  | 3983  |  89 sec. | -f (fast mode)
  	     

  The graph 5 with 75 specified nodes and 3983 edges consists of 21694 internal nodes and 23540 internal edge segments. The tests were done using a xvcg (X11 version, compiled by gcc version 2.6.3, gcc options -O -finline-functions). They were done on a Sparc 10/30 (arch = sun4m) with 32 MB main memory. The times include time for loading, layouting and displaying.
• Time limits can be specified for the layout. If the time limit is exceeded, the tool switches into the fastest and ugliest layout mode.
• The layout algorithm can be controlled in different ways. There are 13 basic layout methods, including a specialized version for trees, and 4 variants of crossing reduction, and various optional optimization methods. Further, the priorities of edges and the number of layout iterations may be set to influence the layout.
• Folding of subgraphs, of dynamically specified regions and the hiding of classes of edges allow to select exactly the part of the graph that is of interest.
• Arbitrary zooming of graphs. Even loadable fonts and icons are fully scalable.
• Color support up to 254 colors out of 16777216 possibilities.
• Different shapes of nodes are available: boxes, triangles, rhombs, ellipses.
• Different kinds of edges are available: Normal edges, near edges, back edges, bent near edges are useful for different applications. Edges can be anchored at the nodes in order to visualize data structures as C structs.
• Edges can be drawn as polygon segments, or as splines. Splines are basically of interest for a quality PostScript output, because the drawing of splines in a X11 window is rather slow.
• Orthogonal layout: here all edges consist of horizontal and vertical edge segments (manhattan layout). In particular, flowcharts look much better in this style.
• It is possible to specify a raster where the centers of the nodes are placed. This may yield in a more uniform layout in some applications.
• Export into PBM-P4 files (black and white) or PNM-P6 files (color). For these formats, there are a lot of converters and printer drivers in the world (for instance, the PBM+ package). Colored multiple page PostScript output up to 25 pages to print very large graphs is possible, too.
• Batch mode printer driver interface to allow to produce an output file of the visualized graph. The VCG tool acts as a kind of converter program in this case: it converts a VCG file into a PostScript or bitmap file. The interactive display is suppressed in this case. This is useful if a large number of VCG specifications must be converted into PostScript or bitmap file by a batch job.
• Fisheye views: If the graph is very large, we normally had only the possibility to see a detail but not the whole graph, or to see the whole graph, but scaled so much that nothing is recognizable. Now, we use fisheyes and see the focus point en detail and the overview over the graph at the same time.
• Interface to program animations that provide the VCG tool with a sequence of graph descriptions.

Examples

Availability

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