feat: show non printable charactors

• If your text file encoding is UTF-8 with BOM, \ufeff is invisible, you don’t known can remove BOM whether or not.
• For indention, you use 4 whitespace instead TAB (\t), but you don’t known current indent delimitor is \t or 4 whitespace.
• For word wrap, if line number is disabled, you don’t known the next line is break word or break by \n.

Describe the solution you’d like

Add a preference to setting non printable chars (such as whitespace, \n, \t…) can show or not.

Describe alternatives you’ve considered

Codemiror (JavaScript edition) ACE editor (JavaScript edition) TextWarrior (Java edition)

    private static final String GLYPH_NEWLINE = "\u21b5"; //↵
    private static final String GLYPH_SPACE = "\u00b7"; //·
    private static final String GLYPH_TAB = "\u00bb"; //»

[massivemadness]

@liyujiang-gzu It works pretty well, but it’s just too laggy when working with large files (especially scrolling), the reason is amount of spans. Right now I have no idea how to optimize this, so I don’t think it would be a good idea to implement this in the next version Here’s the file for tests JavaScriptAPI.zip

P.S I forgot to change tab size on screenshots

[liyujiang-gzu]

Simple code :

            val nonPrintable = Pattern.compile(
                "[\\s\u0000-\u001f\u0020\u007f-\u009f\u00ad\u061c" +
                    "\u200b-\u200f\u2028\u2029\ufeff\ufff9-\ufffc]"
            )
            val matcher = nonPrintable.matcher(text.subSequence(lineStart, lineEnd))
            while (matcher.find()) {
                text.setSpan(
                    NonPrintableSpan(color = "#ff666666".toColorInt()),
                    matcher.start() + lineStart, matcher.end() + lineStart,
                    Spannable.SPAN_INCLUSIVE_INCLUSIVE
                )
            }

/**
 * Created by liyujiang on 2020/08/01
 */
class NonPrintableSpan(@param:ColorInt private val color: Int) : ReplacementSpan() {
    override fun getSize(
        paint: Paint,
        text: CharSequence,
        start: Int,
        end: Int,
        fm: FontMetricsInt?
    ): Int {
        val subSequence = text.subSequence(start, end)
        if (TextUtils.equals(subSequence, "\ufeff")) {
            return paint.measureText(" ").toInt()
        }
        return if (TextUtils.equals(subSequence, "\t")) {
            paint.measureText("    ").toInt()
        } else paint.measureText(subSequence.toString())
            .toInt()
    }

    override fun draw(
        canvas: Canvas, text: CharSequence, start: Int, end: Int,
        x: Float, top: Int, y: Int, bottom: Int, paint: Paint
    ) {
        val subSequence = text.subSequence(start, end)
        val codePoint = Character.codePointAt(subSequence, 0)
        var replaceStr = subSequence.toString()
        when (codePoint) {
            0xfeff -> replaceStr = "\u00a4"
            0x9 -> replaceStr = "\u3009"
            0x20 -> replaceStr = "\u002e"
            else -> {
            }
        }
        paint.color = color
        paint.textSize = 8.dpToPx().toFloat()
        canvas.drawText(replaceStr, x, y.toFloat(), paint)
    }

}