| Author: | Asko Soukka |
|---|---|
| Date-Created: | 2003-08-14 |
| Last-Modified: | 2003-08-15 |
| Revision: | 1.2 |
| Status: | Current |
| Scope: | Trivial |
| Type: | Interface, Feature |
Mudyc asked me to think how the text cursor could be located within a TextNodeView (currently org.fenfire.view.TextNodeView). This PEG describes my solution proposal for solving the problem: two new methods for TextNodeView. One would returning the cursor position according to coordinates within the TextNodeView and another would return the coordinates of the cursor according to it's position (often referred as offset) within the text.
Who is responsible for managing text cursor position? (The term position means here the cursor's offset within the text string.)
RESOLVED: The text cursor position is usually stored within a demo application. Also a spesific Cursor class may be used (org.fengire.view.lava.Cursor).
RE-RESOLVED: Currently the text cursor position is usually stored within a demo application, but Mudyc seems to be developing more general cursor handling in Lava.
But there is also a method getCursorOffset in org.fenfire.view.lava.TextHandler (which the TextNodeView` inherits). Does it have any role?
RESOLVED: AFAIK, currently it's not used anywhere.
RE-RESOLVED: We need to ask Mudyc about the role of TextHandler methods in TextNodeView and also his cursor development in Lava.
Anyway, this peg is not dependent on the way of storing the text cursor position.
Who is responsible for breaking a text string into lines?
RESOLVED: Only the used TextNodeView knows. Currently, it uses LibVob's linebreaking code (org.nongnu.libvob.linebreaking). The linebreaking information is generated only when needed (when creating a Placeable object) and is not stored.
How can the linebreaking information be reached?
RESOLVED: The TextNodeView objects do not store the linebreaking information but can reconstruct it.
Where could the information of linebreaking be reconstructed?
RESOLVED: The reconstruction is complex and is is also most practical to do within TextNodeView, since it has already the supportive methods to help using the linebreaking library.
In TextNodeView only the text content is needed for linebreaking. When creating a placeable TextNodeView object, the text is fetched from the current node (required parameters are current ConstGraph and current node)
When is the linebreaking information needed?
RESOLVED: With mudyc we ended up to two main use cases.
- I know the cursor offset, but in which coordinates I should draw the cursor into?
- I click the text with mouse and know the coordinates I clicked, but how I set the cursor offset according to those coordinates? (this should cover also the selection of text using mouse)
How could the needs be addressed?
RESOLVED: Based on to the previous use cases, I suggest two new methods into TextNodeView. They will reconstruct the linebreaking information using the supportive methods already in TextNodeView and use the public methods of linebreaking.HBroken and linebreaking.HChain to collect the information needed.
The first method returns the cursor position for given coordinates within a TextNodeView and the other returns the coordinates of the cursor given its position (often referred as offset) within the text.
The following (pseudocode) expression should be always true when a proper (existing) text cursor offset value is used:
a == TextNodeView.getPos(TextNodeView.getXY(a))
Into org.fenfire.view.TextNodeView:
/** Get position of the first character placed * after given coordinates. */ public int getPos(ConstGraph g, Object node, float x, float y); /** Get coordinates before the given character position. * The Y coordinate is located below the line. */ public void getXY(ConstGraph g, Object node, int pos, float[] xy);
TextNodeView.getXY() returns the y coordinate located below the line, because linebreaking.Hbroken.getLineOffset() also does that.