Add basic GPOS kerning

stb_truetype.h

@@ -22,6 +22,7 @@
 //   Mikko Mononen: compound shape support, more cmap formats
 //   Tor Andersson: kerning, subpixel rendering
 //   Dougall Johnson: OpenType / Type 2 font handling
+//   Daniel Ribeiro Maciel: basic GPOS-based kerning
 //
 //   Misc other:
 //       Ryan Gordon
@@ -695,7 +696,7 @@ struct stbtt_fontinfo
 
    int numGlyphs;                     // number of glyphs, needed for range checking
 
-   int loca,head,glyf,hhea,hmtx,kern; // table locations as offset from start of .ttf
+   int loca,head,glyf,hhea,hmtx,kern,gpos; // table locations as offset from start of .ttf
    int index_map;                     // a cmap mapping for our chosen character encoding
    int indexToLocFormat;              // format needed to map from glyph index to glyph
 
@@ -1338,6 +1339,7 @@ static int stbtt_InitFont_internal(stbtt_fontinfo *info, unsigned char *data, in
    info->hhea = stbtt__find_table(data, fontstart, "hhea"); // required
    info->hmtx = stbtt__find_table(data, fontstart, "hmtx"); // required
    info->kern = stbtt__find_table(data, fontstart, "kern"); // not required
+   info->gpos = stbtt__find_table(data, fontstart, "GPOS"); // not required
 
    if (!cmap || !info->head || !info->hhea || !info->hmtx)
       return 0;
@@ -2256,7 +2258,7 @@ STBTT_DEF void stbtt_GetGlyphHMetrics(const stbtt_fontinfo *info, int glyph_inde
    }
 }
 
-STBTT_DEF int  stbtt_GetGlyphKernAdvance(const stbtt_fontinfo *info, int glyph1, int glyph2)
+static int  stbtt__GetGlyphKernInfoAdvance(const stbtt_fontinfo *info, int glyph1, int glyph2)
 {
    stbtt_uint8 *data = info->data + info->kern;
    stbtt_uint32 needle, straw;
@@ -2286,9 +2288,242 @@ STBTT_DEF int  stbtt_GetGlyphKernAdvance(const stbtt_fontinfo *info, int glyph1,
    return 0;
 }
 
+static stbtt_int32  stbtt__GetCoverageIndex(stbtt_uint8 *coverageTable, int glyph)
+{
+    stbtt_uint16 coverageFormat = ttUSHORT(coverageTable);
+    switch(coverageFormat) {
+        case 1: {
+            stbtt_uint16 glyphCount = ttUSHORT(coverageTable + 2);
+
+            // Binary search.
+            stbtt_int32 l=0, r=glyphCount-1, m;
+            int straw, needle=glyph;
+            while (l <= r) {
+                m = (l + r) >> 1;
+                stbtt_uint8 *glyphArray = coverageTable + 4;
+                stbtt_uint16 glyphID = ttUSHORT(glyphArray + 2 * m);
+                straw = glyphID;
+                if (needle < straw)
+                    r = m - 1;
+                else if (needle > straw)
+                    l = m + 1;
+                else {
+                     return m;
+                }
+            }
+        } break;
+
+        case 2: {
+            stbtt_uint16 rangeCount = ttUSHORT(coverageTable + 2);
+            stbtt_uint8 *rangeArray = coverageTable + 4;
+
+            // Binary search.
+            stbtt_int32 l=0, r=rangeCount-1, m;
+            int strawStart, strawEnd, needle=glyph;
+            while (l <= r) {
+                m = (l + r) >> 1;
+                stbtt_uint8 *rangeRecord = rangeArray + 6 * m;
+                strawStart = ttUSHORT(rangeRecord);
+                strawEnd = ttUSHORT(rangeRecord + 2);
+                if (needle < strawStart)
+                    r = m - 1;
+                else if (needle > strawEnd)
+                    l = m + 1;
+                else {
+                    stbtt_uint16 startCoverageIndex = ttUSHORT(rangeRecord + 4);
+                    return startCoverageIndex + glyph - strawStart;
+                }
+            }
+        } break;
+
+        default: {
+            // There are no other cases.
+            STBTT_assert(false);
+        } break;
+    }
+
+    return -1;
+}
+
+static stbtt_int32  stbtt__GetGlyphClass(stbtt_uint8 *classDefTable, int glyph)
+{
+    stbtt_uint16 classDefFormat = ttUSHORT(classDefTable);
+    switch(classDefFormat)
+    {
+        case 1: {
+            stbtt_uint16 startGlyphID = ttUSHORT(classDefTable + 2);
+            stbtt_uint16 glyphCount = ttUSHORT(classDefTable + 4);
+            stbtt_uint8 *classDef1ValueArray = classDefTable + 6;
+
+            if (glyph >= startGlyphID && glyph < startGlyphID + glyphCount)
+                return (stbtt_int32)ttUSHORT(classDef1ValueArray + 2 * (glyph - startGlyphID));
+
+            classDefTable = classDef1ValueArray + 2 * glyphCount;
+        } break;
+
+        case 2: {
+            stbtt_uint16 classRangeCount = ttUSHORT(classDefTable + 2);
+            stbtt_uint8 *classRangeRecords = classDefTable + 4;
+
+            // Binary search.
+            stbtt_int32 l=0, r=classRangeCount-1, m;
+            int strawStart, strawEnd, needle=glyph;
+            while (l <= r) {
+                m = (l + r) >> 1;
+                stbtt_uint8 *classRangeRecord = classRangeRecords + 6 * m;
+                strawStart = ttUSHORT(classRangeRecord);
+                strawEnd = ttUSHORT(classRangeRecord + 2);
+                if (needle < strawStart)
+                    r = m - 1;
+                else if (needle > strawEnd)
+                    l = m + 1;
+                else
+                    return (stbtt_int32)ttUSHORT(classRangeRecord + 4);
+            }
+
+            classDefTable = classRangeRecords + 6 * classRangeCount;
+        } break;
+
+        default: {
+            // There are no other cases.
+            STBTT_assert(false);
+        } break;
+    }
+
+    return -1;
+}
+
+// Define to STBTT_assert(x) if you want to break on unimplemented formats.
+#define STBTT_GPOS_TODO_assert(x)
+
+static stbtt_int32  stbtt__GetGlyphGPOSInfoAdvance(const stbtt_fontinfo *info, int glyph1, int glyph2)
+{
+    if (!info->gpos) return 0;
+
+    stbtt_uint8 *data = info->data + info->gpos;
+
+    if (ttUSHORT(data+0) != 1) return 0; // Major version 1
+    if (ttUSHORT(data+2) != 0) return 0; // Minor version 0
+
+    stbtt_uint16 lookupListOffset = ttUSHORT(data+8);
+    stbtt_uint8 *lookupList = data + lookupListOffset;
+
+    stbtt_uint16 lookupCount = ttUSHORT(lookupList);
+    for (stbtt_int32 i=0; i<lookupCount; ++i) {
+        stbtt_uint16 lookupOffset = ttUSHORT(lookupList + 2 + 2 * i);
+        stbtt_uint8 *lookupTable = lookupList + lookupOffset;
+
+        stbtt_uint16 lookupType = ttUSHORT(lookupTable);
+        stbtt_uint16 subTableCount = ttUSHORT(lookupTable + 4);
+        stbtt_uint8 *subTableOffsets = lookupTable + 6;
+        switch(lookupType) {
+            case 2: { // Pair Adjustment Positioning Subtable
+                for (stbtt_int32 sti=0; sti<subTableCount; sti++) {
+                    stbtt_uint16 subtableOffset = ttUSHORT(subTableOffsets + 2 * sti);
+                    stbtt_uint8 *table = lookupTable + subtableOffset;
+                    stbtt_uint16 posFormat = ttUSHORT(table);
+                    stbtt_uint16 coverageOffset = ttUSHORT(table + 2);
+                    stbtt_int32 coverageIndex = stbtt__GetCoverageIndex(table + coverageOffset, glyph1);
+                    if (coverageIndex == -1) continue;
+
+                    switch (posFormat) {
+                        case 1: {
+                            stbtt_uint16 valueFormat1 = ttUSHORT(table + 4);
+                            stbtt_uint16 valueFormat2 = ttUSHORT(table + 6);
+                            // TODO: Support more formats.
+                            STBTT_GPOS_TODO_assert(valueFormat1 == 4);
+                            if (valueFormat1 != 4) return 0;
+                            STBTT_GPOS_TODO_assert(valueFormat2 == 0);
+                            if (valueFormat2 != 0) return 0;
+                            stbtt_int32 valueRecordPairSizeInBytes = 2;
+
+                            stbtt_uint16 pairSetCount = ttUSHORT(table + 8);
+                            STBTT_assert(coverageIndex < pairSetCount);
+                            stbtt_uint16 pairPosOffset = ttUSHORT(table + 10 + 2 * coverageIndex);
+                            stbtt_uint8 *pairValueTable = table + pairPosOffset;
+
+                            stbtt_uint16 pairValueCount = ttUSHORT(pairValueTable);
+                            stbtt_uint8 *pairValueArray = pairValueTable + 2;
+
+                            // Binary search.
+                            stbtt_int32 l=0, r=pairValueCount-1, m;
+                            int straw, needle=glyph2;
+                            while (l <= r) {
+                                m = (l + r) >> 1;
+                                stbtt_uint8 *pairValue = pairValueArray + (2 + valueRecordPairSizeInBytes) * m;
+                                stbtt_uint16 secondGlyph = ttUSHORT(pairValue);
+                                straw = secondGlyph;
+                                if (needle < straw)
+                                    r = m - 1;
+                                else if (needle > straw)
+                                    l = m + 1;
+                                else {
+                                    stbtt_int16 xAdvance = ttSHORT(pairValue + 2);
+                                    return xAdvance;
+                                }
+                            }
+                        } break;
+
+                        case 2: {
+                            stbtt_uint16 valueFormat1 = ttUSHORT(table + 4);
+                            stbtt_uint16 valueFormat2 = ttUSHORT(table + 6);
+                            // TODO: Support more formats.
+                            STBTT_GPOS_TODO_assert(valueFormat1 == 4);
+                            if (valueFormat1 != 4) return 0;
+                            STBTT_GPOS_TODO_assert(valueFormat2 == 0);
+                            if (valueFormat2 != 0) return 0;
+
+                            stbtt_uint16 classDef1Offset = ttUSHORT(table + 8);
+                            stbtt_uint16 classDef2Offset = ttUSHORT(table + 10);
+                            int glyph1class = stbtt__GetGlyphClass(table + classDef1Offset, glyph1);
+                            int glyph2class = stbtt__GetGlyphClass(table + classDef2Offset, glyph2);
+
+                            stbtt_uint16 class1Count = ttUSHORT(table + 12);
+                            stbtt_uint16 class2Count = ttUSHORT(table + 14);
+                            STBTT_assert(glyph1class < class1Count);
+                            STBTT_assert(glyph2class < class2Count);
+
+                            if (glyph1class >= 0 && glyph1class < class1Count && glyph2class >= 0 && glyph2class < class2Count) {
+                                stbtt_uint8 *class1Records = table + 16;
+                                stbtt_uint8 *class2Records = class1Records + 2 * (glyph1class * class2Count);
+                                stbtt_int16 xAdvance = ttSHORT(class2Records + 2 * glyph2class);
+                                return xAdvance;
+                            }
+                        } break;
+
+                        default: {
+                            // There are no other cases.
+                            STBTT_assert(false);
+                        } break;
+                    }
+                }
+            } break;
+
+            default: {
+                // TODO: Implement other stuff.
+            } break;
+        }
+    }
+
+    return 0;
+}
+
+STBTT_DEF int  stbtt_GetGlyphKernAdvance(const stbtt_fontinfo *info, int g1, int g2)
+{
+   int xAdvance = 0;
+
+   if (info->gpos)
+      xAdvance += stbtt__GetGlyphGPOSInfoAdvance(info, g1, g2);
+
+   if (info->kern)
+      xAdvance += stbtt__GetGlyphKernInfoAdvance(info, g1, g2);
+
+   return xAdvance;
+}
+
 STBTT_DEF int  stbtt_GetCodepointKernAdvance(const stbtt_fontinfo *info, int ch1, int ch2)
 {
-   if (!info->kern) // if no kerning table, don't waste time looking up both codepoint->glyphs
+   if (!info->kern && !info->gpos) // if no kerning table, don't waste time looking up both codepoint->glyphs
       return 0;
    return stbtt_GetGlyphKernAdvance(info, stbtt_FindGlyphIndex(info,ch1), stbtt_FindGlyphIndex(info,ch2));
 }