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/*
* This file is subject to the terms of the GFX License. If a copy of
* the license was not distributed with this file, you can obtain one at:
*
* http://ugfx.org/license.html
*/
#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
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