Shaker/Veldrid/Agg/Typography.GlyphLayout/GlyphSetPosition.cs

//MIT, 2016-present, WinterDev
using System.Collections.Generic;
using Typography.OpenFont;
using Typography.OpenFont.Tables;
namespace Typography.TextLayout
{
    /// <summary>
    /// glyph set position manager
    /// </summary>
    class GlyphSetPosition
    {
#if DEBUG
        readonly Typeface dbugTypeface;
#endif

        readonly GPOS _gposTable;
        internal List<GPOS.LookupTable> _lookupTables;
#if DEBUG
        public string dbugScriptLang;
#endif
        public GlyphSetPosition(Typeface typeface, uint scriptTag, uint langTag)
        {
            this.ScriptTag = scriptTag; //script tag
            this.LangTag = langTag; //lang tag

            //check if this lang has
            _gposTable = typeface.GPOSTable;

            if (_gposTable == null) { return; }

            ScriptTable scriptTable = _gposTable.ScriptList[scriptTag];
            if (scriptTable == null) { return; }   // early exit if no lookup tables

            ScriptTable.LangSysTable selectedLang = scriptTable.defaultLang;
            if (selectedLang == null) return; //no default

            if (LangTag != 0 && scriptTable.langSysTables != null)//use default
            {
                //find matching lang
                for (int i = 0; i < scriptTable.langSysTables.Length; ++i)
                {
                    if (scriptTable.langSysTables[i].langSysTagIden == LangTag)
                    {
                        //found
                        selectedLang = scriptTable.langSysTables[i];
                        break;
                    }
                }
            }

#if DEBUG
            dbugTypeface = typeface;
            if (selectedLang.HasRequireFeature)
            {
                System.Diagnostics.Debugger.Break();
            }
#endif
            //other feature
            if (selectedLang.featureIndexList == null) { return; }// early exit

            //---------
            //get features
            _lookupTables = new List<GPOS.LookupTable>();

            for (int i = 0; i < selectedLang.featureIndexList.Length; ++i)
            {
                FeatureList.FeatureTable feature = _gposTable.FeatureList.featureTables[selectedLang.featureIndexList[i]];
                bool includeThisFeature = false;
                switch (feature.TagName)
                {
                    case "mark"://mark=> mark to base
                    case "mkmk"://mkmk => mark to mask
                                //current version we implement this 2 features
                        includeThisFeature = true;
                        break;

                    case "kern":
                        //test with Candara font
                        includeThisFeature = true;
                        //If palt is activated, there is no requirement that kern must also be activated.
                        //If kern is activated, palt must also be activated if it exists.
                        //https://www.microsoft.com/typography/OTSpec/features_pt.htm#palt
                        break;
                    //case "palt":
                    //    break;

                    case "abvm":
                    case "blwm":
                    case "dist":
                        includeThisFeature = true;
                        break;

                    default:
                        System.Diagnostics.Debug.WriteLine("gpos_skip_tag:" + feature.TagName);
                        break;
                }

                if (includeThisFeature)
                {
                    foreach (ushort lookupIndex in feature.LookupListIndices)
                    {
                        _lookupTables.Add(_gposTable.LookupList[lookupIndex]);
                    }
                }
            }
        }
        public uint ScriptTag { get; }
        public uint LangTag { get; }
        public void DoGlyphPosition(IGlyphPositions glyphPositions)
        {
            //early exit if no lookup tables
            //load
            if (_lookupTables == null) { return; }
            //
            int j = _lookupTables.Count;
            for (int i = 0; i < j; ++i)
            {
                _lookupTables[i].DoGlyphPosition(glyphPositions, 0, glyphPositions.Count);
            }
        }
    }
}