GSoC2009 Node Tool Rewrite

This page tracks the progress of the node tool rewrite project which is a part of the Google Summer of Code 2009. This project is being implemented by Krzysztof Kosiński, and the mentor is Bulia Byak. This page will be kept updated with the current status of the student's code (it may not reflect the code in the trunk).

Implementation details

(Work in progress)

Control points (Knots) will be represented by a new class called ControlPoint, based on SPKnot, but with a slightly different set of signals. A set of control points will be managed in a Manipulator. Manipulators can be added and removed from a ManipulatorGroup, which takes care of routing events to them.

A subclass of ControlPoint, SelectableControlPoint, can belong to a ControlPointSelection.

ControlPoint signals

• signal_dragged - emitted when the point is dragged to a new position
• signal_grabbed - start of drag. Emitted when there was a click and a move larger than drag tolerance.
• signal_ungrabbed - end of drag
• signal_moved - knot was moved to new position using the move() method.

Order of emission of drag signals:

• signal_grabbed
• signal_dragged
• signal_dragged
• signal_dragged
• ...
• signal_dragged
• signal_ungrabbed

Examples of implementation

• Dragging out handles: the manipulator connects to signal_clicked, and intercepts it if Shift is held. It then creates a new ControlPoint for the dragged out handle and connects to signal_moved, which is only emitted when the drag is finished. in response to signal_moved, the distance between the node and the handle is checked against the drag tolerance; if it's smaller, the handle is deleted and the path is not updated. If it's larger, repr is updated.

• Constrained dragging: the manipulator connects to signal_dragged. In response to it, it calculates the constrained position, calls setPosition (which doesn't emit any signals) and returns true, which prevents the position from being updated. The events still flow only to the control point due to a pointer grab.

• Handle dragging: A control point representing a node will be subclassed, and will know about its handles. Handles will also be subclassed and know about their nodes. There will be an additional handler for signal_dragged, which will update the position of the other handle appropriately.

Feature Checklist

Feature	Description	Old tool	New tool
Selection
Object selection	Selecting objects to node-edit (incl. Shift-click, Alt-click); ignores groups	Yes	Yes
Selecting single nodes	Whether selecting single nodes with left-click works correctly.	Yes	Yes
Select segment	Click on a path segment to select adjacent nodes. Also works with Shift	Yes	Yes
Selecting multiple nodes	Shift-click to toggle selection of a node	Yes	Yes
Select all	Ctrl+A selects all nodes in subpaths that have something selected, Ctrl+Alt+A selects all nodes	Yes	Yes
Deselect	Esc or click outside of selected paths to deselect	Yes	Yes
Multi-path selection	Selecting nodes in two or more different paths	No	Yes
Rubberband selector	Selecting nodes by dragging anywhere to draw a selection rectangle	Yes	Yes
Prev/Next node	Tab to select next node, Shift+Tab to select previous	Yes	No
Invert Selection	! key inverts node selection in selected subpaths, Alt+! in the whole path	Yes	No
Nodeset selection cue	Whether a selection cue with transform handles can be toggled for sets of nodes (needs sensible behavior when one node is selected)	No	No
Transforms
Move	Moving selections of nodes	Yes	Yes
Move with keyboard	arrows, Shift+arrows, Alt+arrows, Shift+Alt+arrows	Yes	No
Scale with mouse	Scaling node sets with the mouse (needs selection cue)	No	No
Scale with keyboard	Both Ctrl and Alt keys + >, <	Yes	No
Rotate with mouse	Rotating node sets with the mouse	No	No
Rotate with keyboard	Both Ctrl and Alt keys and [, ]	Yes	No
Skew with mouse	Skewing node sets with the mouse	No	No
Skew with keyboard		No	No
Flip nodes	v for vertical flip, h for horizontal	Yes	No
Constrained dragging	Ctrl to restrict movement to axes	Yes	No
Sculpting	Alt to move selected nodes depending on their distance from the cursor	Yes	No
Affect handles	Ability to specify whether handles should be transformed (toggle button)	No	No
Node types
Read node types	Read and store node type information	Yes	Yes
Basic (cusp, smooth, symmetric)	The second handle is modified according to the node type	Yes	Yes
Auto nodes		Yes	Yes
Smooth nodes at ends of linear segments	When a smooth node appears on the end of a linear segment, its handle should remain colinear with the segment when the node or the handle are dragged	Yes	Yes
Set node type	Node type can be set from the toolbar and the handles are updated	Yes	toolbar only
Node actions
Add nodes	Double-click on path segment to add node	Yes	Yes
Delete nodes	Del to remove nodes while trying to preserve shape	Yes	No
Join nodes	Fuse two nodes into one	Yes	No
Multi-path node join	Joining nodes in different paths works sensibly	No	No
Align nodes	Alignment actions in Align and Distribute dialog	Yes	No
Snap nodes	Nodes snap according to snap settings when transformed	Yes	No
Segment actions
Curve drag	Dragging a segment changes its appearance	Yes	Yes
Join segment	Joining two nodes with a segment works correctly	Yes	No
Multi-path segment join	Join between subpaths in different paths works	No	No
Delete segment	Removing a path segment between two nodes	Yes	No
Display
Unselected path outline	Outline promptly flashes when hovering over a unselected path	Yes	No
Selected path outline	Outline of the selected path is drawn	Yes	Yes
Handles
Handle display	Handles are displayed on the selected nodes and their neighbors	Yes	Yes
Flip handles	v for vertical flip, h for horizontal	Yes	No
Lock handle length	Alt to move handles while preserving length	Yes	No
Move along handles	Ctrl+Alt to restrict node movement to the handle lines	Yes	No
Drag out handles	Shift + mouse drag to drag out a handle that coincides with a node	Yes	Yes
Retract handles	Drag a handle near its node to hide it; Retracting both handles of a Bezier segment makes it a line	No	Yes
Restrict movement	Ctrl to restrict handle movements to ~15 degree angle increments from axis-aligned and the original angle	Yes	No
Snap handles	Handles can be snapped to other snap targets	No	No
Copy / paste handles	Ability to copy and paste handles between nodes	No	No
Copy / paste subpaths	Ability to add a subpath by pasting it into the selected path	No	No
Extras
Drag tolerance	Drags shorter than a configurable distance are regarded as clicks	Yes	Yes
Clip / mask editing	Buttons to edit the clipping and masking paths in place	Yes	No
Path effect param editing	Button to to edit the next path parameter of the selected live path effect	Yes	No
Prefs page	Node tool preferences page with various settings	Yes	No

Inkscape key guide for the node tool - more detailed description of the old node tool's features