Thursday, January 6, 2011

QScintilla and getSelection()

The recent Ubuntu upgrade and subsequent Ruby woes were caused, of course, by the desire to install libqscintilla-ruby, a package only available on 10.10 (and even then, only for 1.8).

For the most part, QScintilla works fine in Ruby... until one encounters methods like this:

void getCursorPosition(int *line, int *index) 

void getSelection(int *lineFrom, int *indexFrom, int *lineTo, int *indexTo)

The docs provide some hint as to the problem:

If there is a selection, *lineFrom is set to the line number in which the selection begins and *lineTo is set to the line number in which the selection ends. (They could be the same.) *indexFrom is set to the index at which the selection begins within *lineFrom, and *indexTo is set to the index at which the selection ends within *lineTo. If there is no selection, *lineFrom, *indexFrom, *lineTo and *indexTo are all set to -1.

How does one pass an integer by reference in Ruby?

The answer: one doesn't. These functions take integer arguments and return nil, making them entirely useless in Ruby.

The Python guys did it right:

line_fro, idx_fro, line_to, idx_to = getSelection

The Ruby guys, of course, were lazy, and routed all calls directly to regardless of the sanity of their argument lists.

There is a way to make things work, however, thanks to ScintillaBase.

This, the base class of the Scintilla widget, provides the following method:

long SendScintilla(unsigned int msg, unsigned long wParam=0, long lParam=0)

At the top of  the base class documentation are a bunch of enums that look promising:


Sure enough, these turn out to be the values for the msg parameter.

It makes for short work to add the following methods to the Scintilla object:

def get_sel_start
    self.SendScintilla(2143), 0, 0)

def get_sel_end
    self.SendScintilla(2145), 0, 0)

def get_current_pos
    self.SendScintilla(2008), 0, 0)

Yes, the messages have to be passed by number, as the symbols for the bulk of the messages have not been defined as constants in Ruby (lazy! bad! lazy!), as can be determined by examining Qsci::ScintilaBase.constants.

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