1 files changed, 118 insertions, 0 deletions
diff --git a/src/gdisp/mcufont/mf_kerning.c b/src/gdisp/mcufont/mf_kerning.c
new file mode 100644
index 00000000..bd5afc1a
--- /dev/null
+++ b/src/gdisp/mcufont/mf_kerning.c
@@ -0,0 +1,118 @@
+#include "mf_kerning.h"
+#include <stdbool.h>
+
+#if MF_USE_KERNING
+
+/* Structure for keeping track of the edge of the glyph as it is rendered. */
+struct kerning_state_s
+{
+    uint8_t edgepos[MF_KERNING_ZONES];
+    uint8_t zoneheight;
+};
+
+/* Pixel callback for analyzing the left edge of a glyph. */
+static void fit_leftedge(int16_t x, int16_t y, uint8_t count, uint8_t alpha,
+                         void *state)
+{
+    struct kerning_state_s *s = state;
+    
+    if (alpha > 7)
+    {
+        uint8_t zone = y / s->zoneheight;
+        if (x < s->edgepos[zone])
+            s->edgepos[zone] = x;
+    }
+}
+
+/* Pixel callback for analyzing the right edge of a glyph. */
+static void fit_rightedge(int16_t x, int16_t y, uint8_t count, uint8_t alpha,
+                         void *state)
+{
+    struct kerning_state_s *s = state;
+    
+    if (alpha > 7)
+    {
+        uint8_t zone = y / s->zoneheight;
+        x += count - 1;
+        if (x > s->edgepos[zone])
+            s->edgepos[zone] = x;
+    }
+}
+
+/* Should kerning be done against this character? */
+static bool do_kerning(mf_char c)
+{
+    /* Just a speed optimization, spaces would be ignored anyway. */
+    if (c == ' ' || c == '\n' || c == '\r' || c == '\t')
+        return false;
+    
+    /* Do not kern against digits, in order to keep values in tables nicely
+     * aligned. Most fonts have constant width for digits. */
+    if (c >= '0' && c <= '9')
+        return false;
+    
+    return true;
+}
+
+static int16_t min16(int16_t a, int16_t b) { return (a < b) ? a : b; }
+static int16_t max16(int16_t a, int16_t b) { return (a > b) ? a : b; }
+static int16_t avg16(int16_t a, int16_t b) { return (a + b) / 2; }
+
+int8_t mf_compute_kerning(const struct mf_font_s *font,
+                          mf_char c1, mf_char c2)
+{
+    struct kerning_state_s leftedge, rightedge;
+    uint8_t w1, w2, i, min_space;
+    int16_t normal_space, adjust, max_adjust;
+    
+    if (font->flags & MF_FONT_FLAG_MONOSPACE)
+        return 0; /* No kerning for monospace fonts */
+    
+    if (!do_kerning(c1) || !do_kerning(c2))
+        return 0;
+    
+    /* Compute the height of one kerning zone in pixels */
+    i = (font->height + MF_KERNING_ZONES - 1) / MF_KERNING_ZONES;
+    if (i < 1) i = 1;
+    
+    /* Initialize structures */
+    leftedge.zoneheight = rightedge.zoneheight = i;
+    for (i = 0; i < MF_KERNING_ZONES; i++)
+    {
+        leftedge.edgepos[i] = 255;
+        rightedge.edgepos[i] = 0;
+    }
+    
+    /* Analyze the edges of both glyphs. */
+    w1 = mf_render_character(font, 0, 0, c1, fit_rightedge, &rightedge);
+    w2 = mf_render_character(font, 0, 0, c2, fit_leftedge, &leftedge);
+    
+    /* Find the minimum horizontal space between the glyphs. */
+    min_space = 255;
+    for (i = 0; i < MF_KERNING_ZONES; i++)
+    {
+        uint8_t space;
+        if (leftedge.edgepos[i] == 255 || rightedge.edgepos[i] == 0)
+            continue; /* Outside glyph area. */
+        
+        space = w1 - rightedge.edgepos[i] + leftedge.edgepos[i];
+        if (space < min_space)
+            min_space = space;
+    }
+    
+    if (min_space == 255)
+        return 0; /* One of the characters is space, or both are punctuation. */
+    
+    /* Compute the adjustment of the glyph position. */
+    normal_space = avg16(w1, w2) * MF_KERNING_SPACE_PERCENT / 100;
+    normal_space += MF_KERNING_SPACE_PIXELS;
+    adjust = normal_space - min_space;
+    max_adjust = -max16(w1, w2) * MF_KERNING_LIMIT / 100;
+    
+    if (adjust > 0) adjust = 0;
+    if (adjust < max_adjust) adjust = max_adjust;
+    
+    return adjust;
+}
+
+#endif