Snap to all shapes

Preamble

Summary: Add capability to snap to all shapes when moving or resizing a node or a container.

Relevant tickets:

• Bug 463485 – Snap to all shapes

Introduction

There is currently the capability to snap to shape during moving or resizing a node. This capability is inherited from GMF framework. To enable it, select the diagram and in the Properties view, in Rulers & Grid tab, check the checkbox Snap To Shapes. As explained in GMF doc, However, edit parts can only snap to other edit parts that share the same parent.
The goal of this feature is to enable on demand the snap to all shapes and not only with the same container.

Detailed Specification

This new behavior will be available only if Snap To Shapes is already enabled. To add this new behavior, the user should press a specific shortcut.
Shift, Ctrl and Alt is already used by other GMF behaviors during resize/move. So we must use function key as shortcut. The chosen function key is F4 (not used by other functions on diagram as F5 for refresh for example).

For information the other shortcuts used during resize by GMF or other Sirius features are:

• Control key: Centered resize
• Shift key: Resize that keeps ratio
• Alt key: Resize that disables the snap
• F3: Resize container and keep children relative

For information the other shortcuts used during move by GMF are:

• Shift key: Constrained move
• Alt key (Control key on Mac): Ignore snap while dragging

The Snap To Shapes, uses all the shapes that share the same parent, even if they are not visible.
In contrast, when the user press F4 function key, all visible shapes are used.

As for Snap To Shapes, this feature is available on:

• Node,
• Container,
• List,
• Note,
• Text,
• Bendpoints of edges (but without feedback)

If a container is resized, or moved, it will not be snapped to their children.

Some screenshots of this new feature are shown below.

Known limitations

The Snap To Shapes feature is not operational when moving or resizing a border node. It will be the same for this new feature. However, all nodes can be snapped to existing border nodes.

Backward Compatibility and Migration Paths

This evolution does not change any API.

User Interface Changes

No user interface change.

Documentation Changes

This new behavior should be added in the New and Noteworthy documentation.
A note should also be added in the user doc to explain this new feature (and possibly for the existing move shortcuts):

• Complete chapter Diagram Editors/Features Overview/Resizing elements
• Add new chapter Diagram Editors/Features Overview/Moving elements

Tests and Non-regression strategy

Add new tests that resize elements and move elements. The data from test org.eclipse.sirius.tests.swtbot.PortsOnNodePositionStabilityTest can be used as it uses both nodes, border nodes and container nodes.
Points to consider during tests:

• Shapes not visible in the diagram (they should be ignored by the snap)
• Shapes not visible in a container (they should be ignored by the snap)
• Different zoom levels
• With or without scroll in diagram/in container
• With Control and F4 keys pressed (Control key should disable the snap)

Warning: These tests need to update the SWTBot framework or at least add new methods in our part to drag a node with a shortcut key pressed.

Implementation choices and tradeoffs

Excluded shortcuts:

• The shortcut is not only a character key because this can be in conflict with the direct edit mode (if enabled).
• The combination with ALT key is already used to activate menu.
• The combination with SHIFT key is already used for uppercase key of direct edit mode.
• The combination with CTRL key can conflict with action shortcuts. For example, «CTRL+r» conflicts with the reveal all action.

Excluded behaviors:

• Change the behavior of the Snap To Shapes (instead of add a shortcut)
• Change the UI of Rulers & Grid to show a new Snap To All Shapes checkbox
  • It will not really a checkbox, because it must be exclusive with existing Snap To Shapes checkbox.
  • This also needs to modify global Sirius diagram preferences.