Documentation / Tutorials

Creating a movie with FileSinkImages

We often have to take screenshot of a graph to show it in a presentation or at a moment where it is hard to run the program. Problem is that when we are rendering a dynamic graph, the dynamicity is not rendered in a single screenshot. Movies could be the dynamic screenshot of such graphs.

This tutorial explains how to produce a sequence of images rendering a graph, and how to compil these images to produce a movie.

Choosing when images are produced

The sink needs to know when images have to be outputted. For example, images can be outputted in the following cases:

  • reception of any event ;
  • reception of a node/edge/graph event ;
  • a node/edge is added/removed ;
  • reception of a step event ;
  • …

The enum FileSinkImages.OutputPolicy defines all theses cases.

  • ByEventOutput
  • ByElementEventOutput
  • ByAttributeEventOutput
  • ByNodeEventOutput
  • ByEdgeEventOutput
  • ByGraphEventOutput
  • ByStepOutput
  • ByNodeAddedRemovedOutput
  • ByEdgeAddedRemovedOutput
  • ByNodeAttributeOutput
  • ByEdgeAttributeOutput
  • ByGraphAttributeOutput

The corresponding code is:

  OutputPolicy outputPolicy = OutputPolicy.ByStepOutput;

Choosing the format

Three things have to be defined:

  • prefix of image filenames ;
  • type of images ;
  • resolution of images.

Type of images can be png or jpeg. Types are contained if the enum FileSinkImages.OutputType.

The enum FileSinkImages.Resolutions contains classic resolution:

  • QVGA, 320x240
  • CGA, 320x200
  • VGA, 640x480
  • NTSC, 720x480
  • PAL, 768x576
  • WVGA 5/3, 800x480
  • SVGA, 800x600
  • WVGA 16/9, 854x480
  • WSVGA, 1024x600
  • XGA, 1024x768
  • HD720, 1280x720
  • WXGA 5/3, 1280x768
  • WXGA 8/5, 1280x800
  • SXGA; 1280x1024
  • SXGAp, 1400x1050
  • WSXGAp, 1680x1050
  • UXGA, 1600x1200
  • HD1080, 1920x1080
  • WUXGA, 1920x1200
  • TwoK, 2048x1080
  • QXGA, 2048x1536
  • WQXGA, 2560x1600
  • QSXGA, 2560x2048

but it is possible to define a custom resolution with FileSinkImages.CustomResolution.

The corresponding code is:

 String prefix = "prefix\_";
 OutputType type = OutputType.PNG;
 Resolution resolution = Resolutions.HD720;

Create the FileSinkImages object

This is easily done with the following code :

 FileSinkImages fsi = new FileSinkImages( 
	prefix, type, resolution, outputPolicy );

Choosing a source

The FileSinkImages is a sink and need a source of events. This source could be a graph for example, but it could be a generator, a dgs source, etc…

Using a dgs file allows to avoid the creation of a graph object. This can be usefull when the graph to render is really big and has a high memory cost.

For example :

 FileSourceDGS dgs = new FileSourceDGS();
 
 // Initialization of the sink
 
 dgs.addSink( fsi );
 
 dgs.begin( "path/to/dgs" );
 while( dgs.nextStep() );
 dgs.end();

Set style of graph/nodes/edges

The definition of a style for graph, nodes or edges is allowed by providing a css stylesheet. Syntax is the same that in the GraphStream viewer.

 fsi.setStyleSheet(
 	"graph { padding: 50px; fill-color: black; }" + 
 	"node { fill-color: #3d5689; }" +
 	"edge { fill-color: white; }");

Optionally, enable layout

It is possible to run a layout algorithm. If enabled, the layout can computed in a LayoutRunner or before each image outputted. Layout modes are defined in the enum FileSinkImages.LayoutPolicy:

  • NoLayout, layout is disable ;
  • ComputedInLayoutRunner, layout is computed in a LayoutRunner ;
  • ComputedAtNewImage, layout is computed when a new image is outputted.

Layout policy can changed with the following code :

 fsi.setLayoutPolicy( LayoutPolicy.ComputedAtNewImage );

Optionally, enable high quality rendering

Like in the GraphStream viewer, it is possible to enable an high quality rendering.

This is done by calling setHighQuality() method :

 fsi.setHighQuality();

Sometimes, it could be usefull to add a logo on your movie. The sink provides an easy way to add a logo-image on outputted images. Only pathname of the logo and coordinate on outputted images are needed :

 fsi.addLogo( "path/to/logo", x, y );

Complete example

 // FileSinkImages arguments
 
 OutputPolicy outputPolicy = OutputPolicy.ByStepOutput;
 String prefix = "prefix\_";
 OutputType type = OutputType.PNG;
 Resolution resolution = Resolutions.HD720;
 
 FileSinkImages fsi = new FileSinkImages( type, resolution );
 
 // Create the source
 
 FileSourceDGS dgs = new FileSourceDGS();
  
 // Optional configuration
 
 fsi.setStyleSheet(
 	"graph { padding: 50px; fill-color: black; }" + 
 	"node { fill-color: #3d5689; }" +
 	"edge { fill-color: white; }");
 
 fsi.setOutputPolicy( outputPolicy );
 fsi.setLayoutPolicy( LayoutPolicy.ComputedAtNewImage );
 fsi.setHighQuality();
 fsi.addLogo( "path/to/logo", x, y );
  
 // Images production
 
 dgs.addSink( fsi );
  
 fsi.begin(prefix);
 dgs.begin( "path/to/dgs" );
 while( dgs.nextStep() );
 dgs.end();
 fsi.end();

Create a movie with outputted images

A way to create the movie is using mencoder from the MPlayer Movie Player <http://www.mplayerhq.hu>_

The following bash script compils all images prefix by $PREFIX and ended by $EXT to create an high quality movie $OUPUT :

 #!/bin/bash

 EXT=png
 OPT="vcodec=mpeg4:vqscale=2:vhq:v4mv:trell:autoaspect"
 FPS=15
 PREFIX="prefix\_"
 OUTPUT="graphstream-movie.avi"
 
 mencoder "mf://$PREFIX*.$EXT" -mf fps=$FPS:type=$EXT -ovc lavc -lavcopts $OPT -o $OUTPUT -nosound -vf scale

Make a single screenshot

The writeAll(String) method of the sink can be used to make single screenshot of the graph:

 DefaultGraph g = new DefaultGraph("my beautiful graph");
 FileSinkImages pic = new FileSinkImages(OutputType.PNG, Resolutions.VGA);
 
 pic.setLayoutPolicy(LayoutPolicy.COMPUTED_AT_NEW_IMAGE);
 	
 g.addNode("A");
 g.addNode("B");
 g.addNode("C");
 		
 g.addEdge("AB", "A", "B");
 g.addEdge("AC", "A", "C");
 g.addEdge("BC", "B", "C");
 		
 pic.writeAll(g, "sample.png");