FlexGanttFX Developer Manual : 3.4.6 Activity Rendering

Introduction

The graphics view uses the canvas API of JavaFX. This is due to the complex nature of a Gantt chart and due to the large data volumes often observed inside of them. Directly rendering large quantities of activities into a bitmap is much faster than constantly updating the scene graph and reapplying CSS styling. FlexGanttFX implements a pluggable renderer architecture where renderer instances can be mapped to activity types, very similar to the way Swing was doing it.

The following code is an example of how to register a custom renderer for a given "Flight" activity type. Please note that the graphics view is capable of displaying activities in different layouts, hence the layout type must also be passed to the method.

GraphicsBase<?> graphics = ganttChart.getGraphics();
graphics.setActivityRenderer(
				Flight.class, 
				GanttLayout.class, 
				new FlightRenderer(graphics));

The following methods on GraphicsBase are used for working with renderers:

void setActivityRenderer(...);

ActivityRenderer getActivityRenderer(...);

Drawing

Activity renderers have a single entry point for drawing, a method called draw(). This method is final and can not be overriden. Once invoked it will call various protected methods to perform the actual drawing. The call hierarchy looks like this:

• public final draw()  .... calls ...
  • protected ActivityBounds drawActivity()
    • protected void drawBackground()
    • protected void drawBorder()

Subclasses are free to override any of the three protected methods to customize the activity appearance.

All drawXXX() methods have the same arguments:

ActivityRef<A> activityRef,  // the activity to draw
Position position,			 // agenda layout only (first, middle, last, only)
GraphicsContext gc,		 	 // the graphics context into which to draw
double x,					 // the location of the start time of the activity
double y,					 // the y coordinate (0 when drawn on row or line location)
double w,					 // end time location minus start time location
double h,					 // row or line height
boolean selected,			 // is activity currently selected?
boolean hover,				 // is mouse cursor currently hovering over it?
boolean highlighted,		 // is activity currently blinking?
boolean pressed)			 // is user currently pressing on it?

Default Renderers

The following table lists the various activity renderers that are provided by default.

ActivityRenderer

ActivityBarRenderer

ChartActivityRenderer

CompletableActivityRenderer

 These default renderers are attached to this page and can be downloaded here:

Activity Bounds

Every activity renderer is responsible for returning an instance of ActivityBounds after drawing the activity. These bounds are an essential piece for the framework and many operations will only work properly if these bounds are valid. They are being used for editing activities, for hitpoint detection, for laying out links, for context menus, and so on. The following table lists the attributes of the ActivityBounds class.

Properties

All renderers define several properties that can be used to customize their apperance. Many of these properties are depenent on the "pseudo state" of the activity: hover, pressed, selected, highlighted. To make it easier to lookup the right color at the right time several convenience methods are available:

Renderer

protected Paint getFill(boolean selected,
                        boolean hover,
                        boolean highlighted,
                        boolean pressed);

ActivityRenderer

protected Paint getStroke(boolean selected,
                          boolean hover,
                          boolean highlighted,
                          boolean pressed);

ActivityBarRenderer

protected Paint getTextFill(boolean selected,
                            boolean hover,
                            boolean highlighted,
                            boolean pressed);