3.3. Connector and Connection Types

In MeVisLab, three types of connectors are defined.


In principle, every module type can have any kind of connector.

Table 3.3. Connectors

Look Definition
triangleML images
half-circleInventor scene
squareBase objects: pointers to data structures

ML image connectors can be set to display their state, see Section 4.3.7, “Preferences — Network Appearance”.

Connectors can exist in a semi-transparent design. This is the case if a connector is hidden but connected. An example for a module with Inventor inputs that can be hidden is the View2D modules (see Section 3.9.2, “Additional Inputs”).

Figure 3.3. View2D with Connected "Invisible" Open Inventor Connector

View2D with Connected "Invisible" Open Inventor Connector


Modules with hidden input / output fields can be made to show those fields in different ways.

Some modules provide the option to toggle the visibility of hidden fields in the module's context menu (e.g., View2D, View3D).

Other modules might offer a field on their panel to adjust the number of shown connectors (e.g., Switch).

All modules reveal their hidden input and output connectors when starting to draw a connection in the network. If a module has hidden connectors, an icon appears at the top tight hand corner of such a module. When hovering with the mouse cursor over that icon while still drawing the connection, the module shows all its connectors that are interactively connectable now if the connection is compatible. On establishing the connection, all other hidden connector disappear again.

On pressing the SPACE, the network is rendered in a special information mode where also all invisible connectors are revealed. Pressing CTRL+SPACE shows invisible connectors only. To toggle back to normal view press SPACE again.

To connect to an otherwise invisible connector, start to drag at a source connector. When the drag has been started, modules with invisible connectors show a plus sign at their upper right corner. Move over this plus sign with the connection still dragged; this reveals the hidden connectors of that module. Now, the connection can be established by dropping the connection on the desired destination connector.

Table 3.4. Connecting to an Invisible Connector


In a MeVisLab network, we distinguish between a data connection and a parameter connection.

A data connection connects modules by their input/output connectors. Those connections carry MLi mages, Inventor scene objects, or general Base objects.

A parameter connection connects fields of modules. Such a connection can also connect fields of the same module with each other.

Table 3.5. Connections

Data connections (connector connections)The direct connection between connectors. Depending on which connectors are involved, the connection is rendered in a different color: blue for ML, green for Open Inventor, brown for Base.
Parameter connections (field connections)Connections created by connecting parameter fields within or between modules. For more information, see Section 3.10.2, “Connections Context Menus”.

Data connections are established for example by clicking on a connector and drawing the connection to the other connector. Only connectors of the same kind can be connected.


Refer to Section 3.4, “Connecting, Disconnecting, Moving, and Replacing Connections” for more detailed information on different methods to connect and to disconnect modules.

When interactively connecting Base fields, an internal type system checks whether the particular Base connection is possible.

MeVisLab checks the data types of all available connectors while drawing a connection. Incompatible connectors are rendered in a faded-out style while compatible connectors remain clearly visible.

Figure 3.4. Compatible Connectors for CSOVisualizationSettings Type

Compatible Connectors for CSOVisualizationSettings Type

Figure 3.5. Compatible Connectors for CSOList Type

Compatible Connectors for CSOList Type

Figure 3.6. Compatible Connectors for ML Image Type

Compatible Connectors for ML Image Type


Base connectors can have different data types; connecting these incompatible connectors is possible only via scripting and results in the connection being drawn in red. For more information on Base connectors, see the Getting Started, chapter A Note on Base Types Checks.

Parameter connections are established similarly, by clicking on a field on a panel and drawing the connection to another field (on the same panel or another one). For details on parameter connections, see the Getting Started, chapter Parameter Connection for Synchronization.

Parameter connections can be moved between fields by clicking on the connected connector/field and pressing SHIFT while dragging it to another field. The other connected fields will be updated accordingly.


To abort the interactive establishing and removing of connections between modules (and the horizontal moving of connections), press ESC. Alternatively, abort the establishing by drawing the connection a) to a connector of the wrong type (will be displayed in red) or b) back to the output connector and release the mouse. The new connection will not be drawn, and no existing connections will be removed.