#184 Visible tab stops (tab/space character screen representation)

[BAI Research]

I have created a patch for Nedit 5.7 that supports user change of the screen representation of the tab (\t) and space ( ) white space characters to arbitrary ANSI characters (for example char 187 » and char 183 · respectively).

See https://sourceforge.net/p/nedit/feature-requests/81 for development rationale.

Limitations:

• screen representation of white space characters is currently limited to available ANSI font/motif characters. Ideally the white space replacement characters should be both small and semi-transparent/grey (see TextPad/Textastic show invisible characters implementation for example).

Usage:

• To utilise the patch, apply it to the nedit-5.7 source (eg nedit_5.7.orig.tar.gz), then modify a .Xresources file (and place in $HOME). visibleTabStopsTab/visibleTabStopsSpace are disabled by default (without Xresources parameters). The .Xresources file should include the following parameters:

.Xresources with visibleTabStopsAndSpacesEnabled:

nedit.visibleTabStopsTab: True
nedit.visibleTabStopsTabReplaceFirstCharacterOnly: True
nedit.visibleTabStopsTabReplacementChar: 187
nedit.visibleTabStopsSpace: True
nedit.visibleTabStopsSpaceReplacementChar: 183

.Xresources with visibleTabStopsEnabled:

nedit.visibleTabStopsTab: True
nedit.visibleTabStopsTabReplaceFirstCharacterOnly: True
nedit.visibleTabStopsTabReplacementChar: 183
nedit.visibleTabStopsSpace: False
nedit.visibleTabStopsSpaceReplacementChar: 183

Here is a summary of the changes;

preferences.c;

static struct prefData {
...
~l327:
    int visibleTabStopsTab;
    int visibleTabStopsTabReplaceFirstCharacterOnly;
    int visibleTabStopsTabReplacementChar;
    int visibleTabStopsSpace;
    int visibleTabStopsSpaceReplacementChar;


static PrefDescripRec PrefDescrip[] = {
...
~l1081:
    {"visibleTabStopsTab", "visibleTabStopsTab", PREF_BOOLEAN, "False",
        &PrefData.visibleTabStopsTab, NULL, False},
    {"visibleTabStopsTabReplaceFirstCharacterOnly", "visibleTabStopsTabReplaceFirstCharacterOnly", PREF_BOOLEAN, "True",
        &PrefData.visibleTabStopsTabReplaceFirstCharacterOnly, NULL, False},
    {"visibleTabStopsTabReplacementChar", "visibleTabStopsTabReplacementChar", PREF_INT, "187",
        &PrefData.visibleTabStopsTabReplacementChar, NULL, False},
    {"visibleTabStopsSpace", "visibleTabStopsSpace", PREF_BOOLEAN, "False",
        &PrefData.visibleTabStopsSpace, NULL, False},
    {"visibleTabStopsSpaceReplacementChar", "MaxPrevOpenFiles", PREF_INT, "183",
        &PrefData.visibleTabStopsSpaceReplacementChar, NULL, False},

void RestoreNEditPrefs(XrmDatabase prefDB, XrmDatabase appDB)
    ...
~l1352:
    BufSetVisibleSpaceCharacters(PrefData.visibleTabStopsTab, PrefData.visibleTabStopsTabReplaceFirstCharacterOnly, PrefData.visibleTabStopsTabReplacementChar, PrefData.visibleTabStopsSpace, PrefData.visibleTabStopsSpaceReplacementChar);


textBuf.h;

~l171:
void BufSetVisibleSpaceCharacters(int visibleTabStopsTabNew, int visibleTabStopsTabReplaceFirstCharacterOnlyNew, int visibleTabStopsTabReplacementCharNew, int visibleTabStopsSpaceNew, int visibleTabStopsSpaceReplacementCharNew);


textBuf.c;

~l50:
int visibleTabStopsTab = 0;
int visibleTabStopsTabReplaceFirstCharacterOnly = 0;
char visibleTabStopsTabReplacementChar = '»';   /*(char)187*/
int visibleTabStopsSpace = 0;
char visibleTabStopsSpaceReplacementChar = '·'; /*(char)183*/


~l1050:
int BufExpandCharacter(char c, int indent, char *outStr,
        int tabDist, char nullSubsChar)
{
    int i, nSpaces;

    if(visibleTabStopsSpace) {
        /* show space characters */
        if (c == ' ') {
            *outStr = visibleTabStopsSpaceReplacementChar;
            return 1;
        }
    }

    /* Convert tabs to spaces */
    if (c == '\t') {
        nSpaces = tabDist - (indent % tabDist);
        for (i=0; i<nSpaces; i++) {
            if(visibleTabStopsTab) {
                /* show tab characters */
                if(visibleTabStopsTabReplaceFirstCharacterOnly) {
                    if(i == 0) {
                        outStr[i] = visibleTabStopsTabReplacementChar;
                    }
                    else {
                        outStr[i] = ' ';
                    }
                }
                else {
                    outStr[i] = visibleTabStopsTabReplacementChar;
                }
            }
            else {
                outStr[i] = ' ';
            }
        }
        return nSpaces;
    }

~l2613:
void BufSetVisibleSpaceCharacters(int visibleTabStopsTabNew, int visibleTabStopsTabReplaceFirstCharacterOnlyNew, int visibleTabStopsTabReplacementCharNew, int visibleTabStopsSpaceNew, int visibleTabStopsSpaceReplacementCharNew)
{
    visibleTabStopsTab = visibleTabStopsTabNew;
    visibleTabStopsTabReplaceFirstCharacterOnly = visibleTabStopsTabReplaceFirstCharacterOnlyNew;
    visibleTabStopsTabReplacementChar = visibleTabStopsTabReplacementCharNew;
    visibleTabStopsSpace = visibleTabStopsSpaceNew;
    visibleTabStopsSpaceReplacementChar = visibleTabStopsSpaceReplacementCharNew;
}

[BAI Research]

Patch against 5.7 Master 2020-11-05.