From 45bbf230a523dc2398bb22d82d09ca45edec9047 Mon Sep 17 00:00:00 2001
From: Josh Holtrop <jholtrop@gmail.com>
Date: Sun, 29 Nov 2020 10:37:19 -0500
Subject: [PATCH] Add C Font module for FreeType interface.

---
 Rsconscript        |   1 +
 src/jes/gui/font.c | 129 +++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 130 insertions(+)
 create mode 100644 src/jes/gui/font.c

diff --git a/Rsconscript b/Rsconscript
index afd9cf9..df65825 100644
--- a/Rsconscript
+++ b/Rsconscript
@@ -2,6 +2,7 @@ configure do
   check_d_compiler
   check_lib "X11"
   check_lib "GLX"
+  check_cfg package: "freetype2"
 end
 
 build do
diff --git a/src/jes/gui/font.c b/src/jes/gui/font.c
new file mode 100644
index 0000000..2b94d25
--- /dev/null
+++ b/src/jes/gui/font.c
@@ -0,0 +1,129 @@
+#include <stdint.h>
+#include <stdbool.h>
+#include <stddef.h>
+#include <ft2build.h>
+#include FT_FREETYPE_H
+
+#define round_up_26_6(val) (((val) + 63) >> 6u)
+
+static FT_Library Library_Handle;
+static bool Initialized;
+
+typedef struct
+{
+    FT_Face face;
+    int32_t advance;
+    int32_t line_height;
+    int32_t baseline_offset;
+} Font;
+
+typedef struct
+{
+    uint8_t * bitmap;
+    int32_t width;
+    int32_t height;
+    int32_t left;
+    int32_t top;
+    int32_t advance;
+} Glyph;
+
+static bool Load_FreeType(void)
+{
+    if (Initialized)
+    {
+        return true;
+    }
+
+    if (FT_Init_FreeType(&Library_Handle) != 0)
+    {
+        return false;
+    }
+
+    return Initialized = true;
+}
+
+Glyph * Font_LoadGlyph(Font * font, uint32_t char_code)
+{
+    FT_Char ft_char_code = char_code;
+    if (FT_Load_Char(font->face, ft_char_code, FT_LOAD_RENDER) != 0)
+        return NULL;
+
+    Glyph * glyph = (Glyph *)malloc(sizeof(Glyph));
+    glyph->width = font->face->glyph->bitmap.width;
+    glyph->height = font->face->glyph->bitmap.rows;
+    glyph->left = font->face->glyph->bitmap_left;
+    glyph->top = font->face->glyph->bitmap_top;
+    glyph->advance = round_up_26_6(font->face->glyph->advance.x);
+    glyph->bitmap = malloc(glyph->width * glyph->height);
+    memcpy(glyph->bitmap, font->face->glyph->bitmap.buffer, glyph->width * glyph->height);
+
+    return glyph;
+}
+
+void Font_FreeGlyph(Glyph * glyph)
+{
+    free(glyph->bitmap);
+    free(glyph);
+}
+
+static void PreloadGlyphs(Font * font)
+{
+    static const char preload_glyph_list[] = "HMgjqxy_|^";
+
+    int max_top = -9999;
+    int min_bottom = 9999;
+    font->advance = 0;
+
+    for (size_t i = 0u; i < sizeof(preload_glyph_list) - 1u; i++)
+    {
+        Glyph * glyph = Font_LoadGlyph(font, (uint8_t)preload_glyph_list[i]);
+        if (glyph != NULL)
+        {
+            if (font->face->glyph->bitmap_top > max_top)
+            {
+                max_top = font->face->glyph->bitmap_top;
+            }
+            int bitmap_bottom = font->face->glyph->bitmap_top - font->face->glyph->bitmap.rows;
+            if (bitmap_bottom < min_bottom)
+            {
+                min_bottom = bitmap_bottom;
+            }
+            if (glyph->advance > font->advance)
+            {
+                font->advance = glyph->advance;
+            }
+        }
+    }
+
+    font->line_height = round_up_26_6(font->face->size->metrics.height);
+    font->baseline_offset = (font->line_height - (max_top - min_bottom)) / 2 - min_bottom;
+}
+
+Font * Font_Load(const char * fname, int32_t size)
+{
+    FT_Face face;
+
+    if (!Load_FreeType())
+    {
+        return NULL;
+    }
+
+    if (FT_New_Face(Library_Handle, fname, 0, &face) != 0)
+    {
+        return NULL;
+    }
+
+    Font * font = (Font *)malloc(sizeof(Font));
+    font->face = face;
+
+    FT_Set_Pixel_Sizes(face, 0, size);
+
+    PreloadGlyphs(font);
+
+    return font;
+}
+
+void Font_Free(Font * font)
+{
+    free(font);
+}