In this assignment you will build a JavaFX system that demonstrates your skills with Model-View-Controller and multiple
views, 2D graphics, and interaction with graphical objects. The application, called CriticalPath, allows users to create a
dependency graph for a project and see the critical path from project start to project completion. A dependency graph is
a directed acyclic graph (DAG) where the nodes are activities in the project, and edges connect activities in terms of their
time dependencies. For example, a dependency graph for the task of making a cheese sandwich might be as follows
(note that we assume unlimited workers to carry out the tasks, meaning that all branches can be carried out in parallel):
The critical path is the path through the graph that requires the most total time, and so indicates the total time that will
be needed to complete the project. Since the “toast” path in the graph requires 6 minutes (and the “cheese” path
requires only 4 minutes), the toast path is the critical path. (Note that critical path is calculated only based on time, and
does not care about the number of nodes in the path).
The assignment has 3 parts: Part 1 involves the main UI for creating and working with the graph, Part 2 involves
additional views and navigation, and Part 3 involves graph operations.
Part 1. Main graph UI
The main panel for the system shows the graph and allows the
user to interact with it (i.e., creating and deleting nodes and
edges, dragging nodes on the workspace). The system uses an
MVC architecture as specified below.
The graph view shows a graphical representation of the
graph, with nodes as coloured circles (with titles and
time costs), and edges as arrows between the nodes
The user can create a new node by right-clicking the
mouse (pressing + releasing) on the background. When
a new node is created, it has the default title “Activity”
and the default time cost 1.0
The user can select a node by pressing the left mouse
button on the node; selection is indicated in the view by
drawing the node with a dashed outline and a different
(1 min) Toast bread
(2 min) Slice bread
Retrieve cheese (1 min) Start Slice cheese
(2 min) Butter toast
(1 min) Assemble
The user can move a node by pressing the left mouse button on a node and then dragging the mouse. (This also
selects the node)
Selection is persistent (i.e., the node stays selected even after a move is completed)
The user can delete a node by selecting it and then pressing the Delete key on the keyboard
The user can create an edge by right-clicking on the start node, dragging to the end node, and releasing the
mouse button. As the user drags the mouse, a temporary line is shown from the start node to the mouse cursor;
when the mouse is released on the end node, the edge is created and shown. If the user releases when the
cursor is not on a node, the temporary line is discarded and no edge is created.
Edges show arrowheads to indicate the direction of the edge
The user can select an edge by left-clicking on it (within a small “close enough” region as described in lectures); a
selected edge is shown using a dashed line
The user can delete an edge by selecting it and then pressing the Delete key on the keyboard
Selecting any node or edge removes any previous selection. There is no multiple selection.
When the application starts, the graph contains a single node titled “Start”, with a time cost of 0.0. This is the
root node for calculation of the critical path, and cannot be deleted or edited (however, it can be dragged).
Create class MainGraphView to show the graph
o The view must use immediate-mode graphics in JavaFX (i.e., a Canvas)
o The view should use 2D transforms to position the graphics reference frame before drawing nodes,
edges, and arrowheads
Create class GraphModel to store the graph
o Create classes Node and Edge that will be used by the model
o GraphModel must use publish-subscribe communication to the view
o GraphModel must have a public API that can be called by the controller
o The model must store locations as normalized coordinates
Create class GraphViewController to handle user events from the MainGraphView
o The controller must implement a state machine to handle mouse events from the MainGraphView
o Note: when you set up event handling in MainGraphView, normalize the mouse coordinates before they
are sent to the controller (as shown in the lab example).
Create class InteractionModel to store view state including node and edge selection
Resources for Part 1
The BoxDemo code and the graphics demos available in the Code Examples folder on the course website
JavaFX APIs for Canvas and GraphicsContext: openjfx.io/javadoc/15/
Result for Part 1: a zipped IDEA project that meets the interaction and code requirements above. To export your project,
choose File Export Project to Zip file. NOTE: if you have fully completed Part 2, do not hand in a project for Part 1.
Part 2. Additional views and viewport navigation
In Part 2 you will create additional views for the CriticalPath app, and will implement panning and zooming capability.
There will be two new views of the graph (a view of a single node’s details, and an overview of the entire workspace),
and you will combine these and your existing graph view into a new composite view that holds the entire UI.
MainGraphView: new interaction requirements
The graph is now shown on a square workspace that may be larger than the MainGraphView’s canvas, and
therefore the MainGraphView now shows a viewport onto the workspace. For example, the workspace might be
2000×2000, and a 500×500 MainGraphView will show one quarter of the workspace.
The viewport can now be panned: when the user presses on the background (either mouse button) and drags,
the view will pan by the amount of the drag.
Panning is restricted to the size of the workspace (i.e., the left/top of the MainGraphView can never go past 0,0
in the workspace, and the right/bottom of the MainGraphView can never go past the workspace extents)
If the window is resized, the size of the
MainGraphView canvas changes, but not the
size of the workspace.
MainGraphView: new code requirements
Add variables to MainGraphView to store the
size of a logical workspace that can be different
from the size of the MainGraphView. (You may
wish to also store the workspace size in the
Use the width and height of the workspace as
the extents for normalizing coordinates (i.e.,
divide the mouse X and Y by the workspace
width and height, rather than the
MainGraphView width and height)
Add viewportLeft and viewportTop variables to
the InteractionModel to store the left and top
coordinates of the viewport within the workspace
When you draw the graph in the MainGraphView, subtract viewportLeft and viewportTop from your translations
in order to draw the correct content in the MainGraphView. For example, assume the workspace is 2000×2000
and the MainGraphView is 500×500. Assume a Node has location 0.5, 0.5 in the workspace, and that the
viewport is at viewportLeft 0.4 and viewportTop 0.4. The Node should be therefore be drawn in the
MainGraphView at x = (0.5 – 0.4) * 500 and y = (0.5 – 0.4) * 500.
Create class NodeDetailView to show the name and time cost for a selected node
Lay out the components of NodeDetailView as shown in the picture
If no node is selected, this view should show blanks for both name and time
The text fields in the NodeDetailView are editable: if the user enters a new name and presses Return, or enters a
new cost and presses Return, the selected node will be updated with the new values. (Note that using Return to
generate an event in a TextField can be done with the setOnAction() method.)
If the user attempts to edit the Start node, the values return to their defaults (“Start” and 0.0)
Create class MiniGraphView to show an overview of the entire workspace
The mini view should be very similar to the MainGraphView, with the following changes:
o The mini view is 200×200 pixels, and does not change size
o The mini view always shows the entire workspace
o The mini view shows the MainGraphView’s viewport as a transparent grey rectangle
o There are no user interactions with the mini view.
You may wish to create an inheritance hierarchy to avoid duplicating code for the two graph views (e.g.,
MainGraphView and MiniGraphView both extend abstract GraphView)
Composite app view:
Create class MainAppView that will hold your other views and additional controls
Lay out the views inside MainAppView as shown in the picture
Add a panel “View Controls” between the mini view and the node view
o The view controls should show a slider with extents [0.25..2.0]
o Dragging the slider changes the zoom level in the MainGraphView (and also changes the size of the
viewport rectangle in the mini view). Add a variable zoomLevel to InteractionModel to store this value.
Resources for Part 2
The lab demonstration of composite views, and the view-control demo code available in the Code Examples
folder on the course website
Result for Part 2: a zipped IDEA project that meets the interaction and code requirements above. To export your project,
choose File Export Project to Zip file. NOTE: if you have fully completed Part 3, do not hand in a project for Part 2.
Part 3. Graph operations: detecting cycles and finding the critical path
Add methods to your CriticalPath app to check for cycles and to calculate the critical path, and add to your view classes
to highlight the critical path through the graph.
Detect cycles on edge creation:
Dependency graphs that calculate critical paths must be acyclic (an example of
a cycle is shown in the picture at right)
Add code to check for cycles whenever an edge is added to the graph. If
adding the new edge results in a cycle, undo the addition of the edge
Use recursive depth-first traversal to check for cycles:
o In class Node, add boolean instance variables visited and exploring
o In class GraphModel, add method boolean checkForCycles() that first
sets the visited and exploring flags of all Nodes to false, and then calls
findCycles() on the start node.
o In class Node, add method findCycles() that implements the following algorithm:
if this node’s visited flag is true, return false
if this node’s exploring flag is true, return true
set this node’s exploring flag to true
for each outgoing edge:
if findCycles() on the end Node of this edge is true, return true
set this node’s visited flag to true
Calculate the critical path:
Whenever an edge is added or a time cost is edited, recalculate the graph’s critical path
Create class GraphPath to store a path through the graph
o This class should have instance variables to store a list of Nodes, a list of Edges, and a total cost
In class GraphModel, create method findCriticalPath() that does the following:
o Create a new Path current and add the Start node to the path
o Create a list of Path objects allPaths
o Call findPaths(current, allPaths) on the Start node
o Iterate through the paths in allPaths and calculate the total cost for each path
o The path with the highest cost is the critical path; store this path in the GraphModel
In class Node, create method findPaths(Path currentPath, List allPaths) that implements the following:
o if this node has no outgoing edges, add the current path to allPaths and return
o for each outgoing edge:
create a new Path continuePath and copy the nodes and edges from currentPath
add the current edge’s end node to continuePath’s nodes
add the current edge to continuePath’s edges
call findPaths on the edge’s end node, passing in continuePath and allPaths
In your view classes, when you draw nodes and edges, check whether they are in the critical path; if they are,
draw them with a different stroke colour
Resources for Part 3
Start Activity 1.0
Result for Part 3: a zipped IDEA project that meets
the interaction and code requirements above. To
export your project, choose File Export
Project to Zip file.
What to hand in
Note that this assignment is to be done
individually; each student will hand in an
A zip file of your IDEA project folder and a
readme.txt file that indicates exactly what
the marker needs to do to run your code.
(Systems for 381 should never require the
marker to install external libraries, other
You only need to hand in one project if
that project represents everything you have completed on the assignment. However, if you have completed
different elements from different parts of the assignment, or if there are bugs in one part of your solution, you
can hand in multiple zipfiles to demonstrate the parts that you have completed. (If this is the case, state in your
readme.txt file which features are available in which projects)
Where to hand in
Hand in your files to the link on the course website.
Marks will be given for: producing a system that runs without errors; demonstrating that you can develop MVC-based
systems with 2D interactive graphics; demonstrating that you can develop multiple views and composite views;
demonstrating that you can work with view geometry and navigation at multiple scales.
Weighting of the parts in the overall grade: Part 1=35%, Part 2=50%, Part 3=15%.
Note that no late assignments will be allowed, and no extensions will be given, without medical reasons.