rewrite comment explaining DocIterator's boundary_

All boundary-related code went through a major rehaul some months ago (mainly
Stefan's work), but this comment was never updated to reflect that.


git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@22730 a592a061-630c-0410-9148-cb99ea01b6c8
This commit is contained in:
Dov Feldstern 2008-01-31 22:50:16 +00:00
parent 796092635f
commit 32fe049333

View File

@ -225,19 +225,29 @@ public:
private: private:
/** /**
* When the cursor position is i, is the cursor after the i-th char * Normally, when the cursor is at position i, it is painted *before*
* or before the i+1-th char ? Normally, these two interpretations are * the character at position i. However, what if we want the cursor
* equivalent, except when the fonts of the i-th and i+1-th char * painted *after* position i? That's what boundary_ is for: if
* differ. * boundary_==true, the cursor is painted *after* position i-1, instead
* We use boundary_ to distinguish between the two options: * of before position i.
* If boundary_=true, then the cursor is after the i-th char
* and if boundary_=false, then the cursor is before the i+1-th char.
* *
* We currently use the boundary only when the language direction of * Note 1: Usually, after i-1 or before i are actually the same place!
* the i-th char is different than the one of the i+1-th char. * However, this is not the case when i-1 and i are not painted
* In this case it is important to distinguish between the two * contiguously, and in these cases we sometimes do want to have control
* cursor interpretations, in order to give a reasonable behavior to * over whether to paint before i or after i-1.
* the user. * Some concrete examples of where this happens:
* a. i-1 at the end of one row, i at the beginning of next row
* b. in bidi text, at transitions between RTL and LTR or vice versa
*
* Note 2: Why i and i-1? Why, if boundary_==false means: *before* i,
* couldn't boundary_==true mean: *after* i?
* Well, the reason is this: cursor position is not used only for
* painting the cursor, but it also affects other things, for example:
* where the next insertion will be placed (it is inserted at the current
* position, pushing anything at the current position and beyond forward).
* Now, when the current position is i and boundary_==true, insertion would
* happen *before* i. If the cursor, however, were painted *after* i, that
* would be very unnatural...
*/ */
bool boundary_; bool boundary_;
/// ///