Apply Ligatures patch

Homepage link: https://st.suckless.org/patches/ligatures/
Patch links:
    https://st.suckless.org/patches/ligatures/0.8.3/st-ligatures-boxdraw-20200430-0.8.3.diff
    https://st.suckless.org/patches/ligatures/0.8.3/st-ligatures-scrollback-20200430-0.8.3.diff
Additional info: the patch was applied by mixing the two patches linked
above in order to provide compatibility with both BoxDraw and Scrollback
patches.

9 files changed, 179 insertions, 15 deletions

diff --git a/Makefile b/Makefile
index 8a2e1f9..8fe1520 100644
--- a/Makefile
+++ b/Makefile
@@ -4,7 +4,7 @@
 
 include config.mk
 
-SRC = st.c x.c boxdraw.c
+SRC = st.c x.c boxdraw.c hb.c
 OBJ = $(SRC:.c=.o)
 
 all: options st
@@ -22,7 +22,8 @@ config.h:
         $(CC) $(STCFLAGS) -c $<
 
 st.o: config.h st.h win.h
-x.o: arg.h config.h st.h win.h
+x.o: arg.h config.h st.h win.h hb.h
+hb.o: st.h
 boxdraw.o: config.h st.h boxdraw_data.h
 
 $(OBJ): config.h config.mk
diff --git a/README.md b/README.md
index 7c658ea..7796f3a 100644
--- a/README.md
+++ b/README.md
@@ -13,6 +13,8 @@ were applied.
   buffer scrollback.
 + [boxdraw](https://st.suckless.org/patches/boxdraw/) - handles
   line/box/braille drawings
++ [ligatures](https://st.suckless.org/patches/ligatures/) - add ligature
+  support
 
 Requirements
 ------------
diff --git a/config.mk b/config.mk
index 5d202e5..d058753 100644
--- a/config.mk
+++ b/config.mk
@@ -15,10 +15,12 @@ PKG_CONFIG = pkg-config
 # includes and libs
 INCS = -I$(X11INC) \
        `$(PKG_CONFIG) --cflags fontconfig` \
-       `$(PKG_CONFIG) --cflags freetype2`
+           `$(PKG_CONFIG) --cflags freetype2` \
+           `$(PKG_CONFIG) --cflags harfbuzz`
 LIBS = -L$(X11LIB) -lm -lrt -lX11 -lutil -lXft \
        `$(PKG_CONFIG) --libs fontconfig` \
-       `$(PKG_CONFIG) --libs freetype2`
+       `$(PKG_CONFIG) --libs freetype2` \
+           `$(PKG_CONFIG) --libs harfbuzz`
 
 # flags
 STCPPFLAGS = -DVERSION=\"$(VERSION)\" -D_XOPEN_SOURCE=600
diff --git a/hb.c b/hb.c
new file mode 100644
index 0000000..467bcac
--- /dev/null
+++ b/hb.c
@@ -0,0 +1,140 @@
+#include <stdlib.h>
+#include <stdio.h>
+#include <math.h>
+#include <X11/Xft/Xft.h>
+#include <hb.h>
+#include <hb-ft.h>
+
+#include "st.h"
+
+void hbtransformsegment(XftFont *xfont, const Glyph *string, hb_codepoint_t *codepoints, int start, int length);
+hb_font_t *hbfindfont(XftFont *match);
+
+typedef struct {
+        XftFont *match;
+        hb_font_t *font;
+} HbFontMatch;
+
+static int hbfontslen = 0;
+static HbFontMatch *hbfontcache = NULL;
+
+void
+hbunloadfonts()
+{
+        for (int i = 0; i < hbfontslen; i++) {
+                hb_font_destroy(hbfontcache[i].font);
+                XftUnlockFace(hbfontcache[i].match);
+        }
+
+        if (hbfontcache != NULL) {
+                free(hbfontcache);
+                hbfontcache = NULL;
+        }
+        hbfontslen = 0;
+}
+
+hb_font_t *
+hbfindfont(XftFont *match)
+{
+        for (int i = 0; i < hbfontslen; i++) {
+                if (hbfontcache[i].match == match)
+                        return hbfontcache[i].font;
+        }
+
+        /* Font not found in cache, caching it now. */
+        hbfontcache = realloc(hbfontcache, sizeof(HbFontMatch) * (hbfontslen + 1));
+        FT_Face face = XftLockFace(match);
+        hb_font_t *font = hb_ft_font_create(face, NULL);
+        if (font == NULL)
+                die("Failed to load Harfbuzz font.");
+
+        hbfontcache[hbfontslen].match = match;
+        hbfontcache[hbfontslen].font = font;
+        hbfontslen += 1;
+
+        return font;
+}
+
+void
+hbtransform(XftGlyphFontSpec *specs, const Glyph *glyphs, size_t len, int x, int y)
+{
+        int start = 0, length = 1, gstart = 0;
+        hb_codepoint_t *codepoints = calloc(len, sizeof(hb_codepoint_t));
+
+        for (int idx = 1, specidx = 1; idx < len; idx++) {
+                if (glyphs[idx].mode & ATTR_WDUMMY) {
+                        length += 1;
+                        continue;
+                }
+
+                if (specs[specidx].font != specs[start].font || ATTRCMP(glyphs[gstart], glyphs[idx]) || selected(x + idx, y) != selected(x + gstart, y)) {
+                        hbtransformsegment(specs[start].font, glyphs, codepoints, gstart, length);
+
+                        /* Reset the sequence. */
+                        length = 1;
+                        start = specidx;
+                        gstart = idx;
+                } else {
+                        length += 1;
+                }
+
+                specidx++;
+        }
+
+        /* EOL. */
+        hbtransformsegment(specs[start].font, glyphs, codepoints, gstart, length);
+
+        /* Apply the transformation to glyph specs. */
+        for (int i = 0, specidx = 0; i < len; i++) {
+                if (glyphs[i].mode & ATTR_WDUMMY)
+                        continue;
+                if (glyphs[i].mode & ATTR_BOXDRAW) {
+                        specidx++;
+                        continue;
+                }
+
+                if (codepoints[i] != specs[specidx].glyph)
+                        ((Glyph *)glyphs)[i].mode |= ATTR_LIGA;
+
+                specs[specidx++].glyph = codepoints[i];
+        }
+
+        free(codepoints);
+}
+
+void
+hbtransformsegment(XftFont *xfont, const Glyph *string, hb_codepoint_t *codepoints, int start, int length)
+{
+        hb_font_t *font = hbfindfont(xfont);
+        if (font == NULL)
+                return;
+
+        Rune rune;
+        ushort mode = USHRT_MAX;
+        hb_buffer_t *buffer = hb_buffer_create();
+        hb_buffer_set_direction(buffer, HB_DIRECTION_LTR);
+
+        /* Fill buffer with codepoints. */
+        for (int i = start; i < (start+length); i++) {
+                rune = string[i].u;
+                mode = string[i].mode;
+                if (mode & ATTR_WDUMMY)
+                        rune = 0x0020;
+                hb_buffer_add_codepoints(buffer, &rune, 1, 0, 1);
+        }
+
+        /* Shape the segment. */
+        hb_shape(font, buffer, NULL, 0);
+
+        /* Get new glyph info. */
+        hb_glyph_info_t *info = hb_buffer_get_glyph_infos(buffer, NULL);
+
+        /* Write new codepoints. */
+        for (int i = 0; i < length; i++) {
+                hb_codepoint_t gid = info[i].codepoint;
+                codepoints[start+i] = gid;
+        }
+
+        /* Cleanup. */
+        hb_buffer_destroy(buffer);
+}
diff --git a/hb.h b/hb.h
new file mode 100644
index 0000000..07888df
--- /dev/null
+++ b/hb.h
@@ -0,0 +1,6 @@
+#include <X11/Xft/Xft.h>
+#include <hb.h>
+#include <hb-ft.h>
+
+void hbunloadfonts();
+void hbtransform(XftGlyphFontSpec *, const Glyph *, size_t, int, int);
diff --git a/st.c b/st.c
index 1a3f49c..4a6c2c9 100644
--- a/st.c
+++ b/st.c
@@ -2665,7 +2665,8 @@ draw(void)
         drawregion(0, 0, term.col, term.row);
     if (term.scr == 0)
             xdrawcursor(cx, term.c.y, term.line[term.c.y][cx],
-                    term.ocx, term.ocy, term.line[term.ocy][term.ocx]);
+                        term.ocx, term.ocy, term.line[term.ocy][term.ocx],
+                        term.line[term.ocy], term.col);
         term.ocx = cx, term.ocy = term.c.y;
         xfinishdraw();
         xximspot(term.ocx, term.ocy);
diff --git a/st.h b/st.h
index e9b3abe..70ebea0 100644
--- a/st.h
+++ b/st.h
@@ -4,17 +4,18 @@
 #include <sys/types.h>
 
 /* macros */
-#define MIN(a, b)               ((a) < (b) ? (a) : (b))
-#define MAX(a, b)               ((a) < (b) ? (b) : (a))
-#define LEN(a)                  (sizeof(a) / sizeof(a)[0])
+#define MIN(a, b)                   ((a) < (b) ? (a) : (b))
+#define MAX(a, b)                   ((a) < (b) ? (b) : (a))
+#define LEN(a)                      (sizeof(a) / sizeof(a)[0])
 #define BETWEEN(x, a, b)        ((a) <= (x) && (x) <= (b))
 #define DIVCEIL(n, d)           (((n) + ((d) - 1)) / (d))
 #define DEFAULT(a, b)           (a) = (a) ? (a) : (b)
 #define LIMIT(x, a, b)          (x) = (x) < (a) ? (a) : (x) > (b) ? (b) : (x)
-#define ATTRCMP(a, b)           ((a).mode != (b).mode || (a).fg != (b).fg || \
-                                (a).bg != (b).bg)
+#define ATTRCMP(a, b)       (((a).mode & (~ATTR_WRAP) & (~ATTR_LIGA)) != ((b).mode & (~ATTR_WRAP) & (~ATTR_LIGA)) || \
+                            (a).fg != (b).fg || \
+                                            (a).bg != (b).bg)
 #define TIMEDIFF(t1, t2)        ((t1.tv_sec-t2.tv_sec)*1000 + \
-                                (t1.tv_nsec-t2.tv_nsec)/1E6)
+                                            (t1.tv_nsec-t2.tv_nsec)/1E6)
 #define MODBIT(x, set, bit)     ((set) ? ((x) |= (bit)) : ((x) &= ~(bit)))
 
 #define TRUECOLOR(r,g,b)        (1 << 24 | (r) << 16 | (g) << 8 | (b))
@@ -34,6 +35,7 @@ enum glyph_attribute {
         ATTR_WIDE       = 1 << 9,
         ATTR_WDUMMY     = 1 << 10,
     ATTR_BOXDRAW    = 1 << 11,
+    ATTR_LIGA       = 1 << 12,
         ATTR_BOLD_FAINT = ATTR_BOLD | ATTR_FAINT,
 };
 
diff --git a/win.h b/win.h
index a6ef1b9..bc0d180 100644
--- a/win.h
+++ b/win.h
@@ -25,7 +25,7 @@ enum win_mode {
 
 void xbell(void);
 void xclipcopy(void);
-void xdrawcursor(int, int, Glyph, int, int, Glyph);
+void xdrawcursor(int, int, Glyph, int, int, Glyph, Line, int);
 void xdrawline(Line, int, int, int);
 void xfinishdraw(void);
 void xloadcols(void);
diff --git a/x.c b/x.c
index 58c2d98..0f95d60 100644
--- a/x.c
+++ b/x.c
@@ -19,6 +19,7 @@ static char *argv0;
 #include "arg.h"
 #include "st.h"
 #include "win.h"
+#include "hb.h"
 
 /* types used in config.h */
 typedef struct {
@@ -1117,6 +1118,9 @@ xunloadfont(Font *f)
 void
 xunloadfonts(void)
 {
+    /* Clear Harfbuzz font cache. */
+    hbunloadfonts();
+
         /* Free the loaded fonts in the font cache.  */
         while (frclen > 0)
                 XftFontClose(xw.dpy, frc[--frclen].font);
@@ -1320,7 +1324,7 @@ xmakeglyphfontspecs(XftGlyphFontSpec *specs, const Glyph *glyphs, int len, int x
                 mode = glyphs[i].mode;
 
                 /* Skip dummy wide-character spacing. */
-                if (mode == ATTR_WDUMMY)
+        if (mode & ATTR_WDUMMY)
                         continue;
 
                 /* Determine font for glyph if different from previous glyph. */
@@ -1432,6 +1436,9 @@ xmakeglyphfontspecs(XftGlyphFontSpec *specs, const Glyph *glyphs, int len, int x
                 numspecs++;
         }
 
+    /* Harfbuzz transformation for ligatures. */
+    hbtransform(specs, glyphs, len, x, y);
+
         return numspecs;
 }
 
@@ -1585,14 +1592,17 @@ xdrawglyph(Glyph g, int x, int y)
 }
 
 void
-xdrawcursor(int cx, int cy, Glyph g, int ox, int oy, Glyph og)
+xdrawcursor(int cx, int cy, Glyph g, int ox, int oy, Glyph og, Line line, int len)
 {
         Color drawcol;
 
         /* remove the old cursor */
         if (selected(ox, oy))
                 og.mode ^= ATTR_REVERSE;
-        xdrawglyph(og, ox, oy);
+
+    /* Redraw the line where cursor was previously.
+     * It will restore the ligatures broken by the cursor. */
+    xdrawline(line, 0, oy, len);
 
         if (IS_SET(MODE_HIDE))
                 return;