Implement optional font rendering options

The user can now choose antialiasing grayscale and subpixel and hinting
non, slight or full.

data/core/style.lua

@@ -7,9 +7,23 @@ style.scrollbar_size = common.round(4 * SCALE)
 style.caret_width = common.round(2 * SCALE)
 style.tab_width = common.round(170 * SCALE)
 
+-- The function renderer.font.load can accept an option table as a second optional argument.
+-- It shoud be like the following:
+--
+-- {antialiasing= "grayscale", hinting = "full"}
+--
+-- The possible values for each option are:
+-- - for antialiang: grayscale, subpixel
+-- - for hinting: none, slight, full
+--
+-- The defaults values are antialiang subpixel and hinting slight for optimal visualization
+-- on ordinary LCD monitor with RGB patterns.
+--
+-- On High DPI monitor or non RGB monitor you may consider using antialiang grayscale instead.
+-- The antialising grayscale with full hinting is interesting for crisp font rendering.
 style.font = renderer.font.load(DATADIR .. "/fonts/font.ttf", 14 * SCALE)
 style.big_font = renderer.font.load(DATADIR .. "/fonts/font.ttf", 34 * SCALE)
-style.icon_font = renderer.font.load(DATADIR .. "/fonts/icons.ttf", 14 * SCALE)
+style.icon_font = renderer.font.load(DATADIR .. "/fonts/icons.ttf", 14 * SCALE, {antialiasing="grayscale", hinting="full"})
 style.code_font = renderer.font.load(DATADIR .. "/fonts/monospace.ttf", 13.5 * SCALE)
 
 style.background = { common.color "#2e2e32" }

src/api/renderer_font.c

@@ -6,9 +6,43 @@
 static int f_load(lua_State *L) {
   const char *filename  = luaL_checkstring(L, 1);
   float size = luaL_checknumber(L, 2);
+  unsigned int font_options = 0;
+  if (lua_gettop(L) > 2 && lua_istable(L, 3)) {
+    lua_getfield(L, 3, "antialiasing");
+    if (lua_isstring(L, -1)) {
+      const char *antialiasing = lua_tostring(L, -1);
+      if (antialiasing) {
+        if (strcmp(antialiasing, "grayscale") == 0) {
+          font_options |= RenFontGrayscale;
+        } else if (strcmp(antialiasing, "subpixel") == 0) {
+          font_options |= RenFontSubpixel;
+        } else {
+          return luaL_error(L, "error in renderer.font.load, unknown antialiasing option: \"%s\"", antialiasing);
+        }
+      }
+    }
+    lua_pop(L, 1);
+
+    lua_getfield(L, 3, "hinting");
+    if (lua_isstring(L, -1)) {
+      const char *hinting = lua_tostring(L, -1);
+      if (hinting) {
+        if (strcmp(hinting, "slight") == 0) {
+          font_options |= RenFontHintingSlight;
+        } else if (strcmp(hinting, "none") == 0) {
+          font_options |= RenFontHintingNone;
+        } else if (strcmp(hinting, "full") == 0) {
+          font_options |= RenFontHintingFull;
+        } else {
+          return luaL_error(L, "error in renderer.font.load, unknown hinting option: \"%s\"", hinting);
+        }
+      }
+    }
+    lua_pop(L, 1);
+  }
   RenFont **self = lua_newuserdata(L, sizeof(*self));
   luaL_setmetatable(L, API_TYPE_FONT);
-  *self = ren_load_font(filename, size);
+  *self = ren_load_font(filename, size, font_options);
   if (!*self) { luaL_error(L, "failed to load font"); }
   return 1;
 }

src/renderer.c

@@ -141,14 +141,23 @@ static GlyphSet* get_glyphset(RenFont *font, int codepoint) {
 }
 
 
-RenFont* ren_load_font(const char *filename, float size) {
+RenFont* ren_load_font(const char *filename, float size, unsigned int renderer_flags) {
   RenFont *font = NULL;
 
   /* init font */
   font = check_alloc(calloc(1, sizeof(RenFont)));
   font->size = size;
 
-  font->renderer = FR_Renderer_New(FR_HINTING | FR_SUBPIXEL | FR_PRESCALE_X);
+  unsigned int fr_renderer_flags = 0;
+  if ((renderer_flags & RenFontAntialiasingMask) == RenFontSubpixel) {
+    fr_renderer_flags |= FR_SUBPIXEL;
+  }
+  if ((renderer_flags & RenFontHintingMask) == RenFontHintingSlight) {
+    fr_renderer_flags |= (FR_HINTING | FR_PRESCALE_X);
+  } else if ((renderer_flags & RenFontHintingMask) == RenFontHintingFull) {
+    fr_renderer_flags |= FR_HINTING;
+  }
+  font->renderer = FR_Renderer_New(fr_renderer_flags);
   if (FR_Load_Font(font->renderer, filename)) {
     free(font);
     return NULL;

src/renderer.h

@@ -7,6 +7,17 @@
 typedef struct RenImage RenImage;
 typedef struct RenFont RenFont;
 
+enum {
+  RenFontAntialiasingMask = 1,
+  RenFontGrayscale        = 1,
+  RenFontSubpixel         = 0,
+
+  RenFontHintingMask   = 3 << 1,
+  RenFontHintingSlight = 0 << 1,
+  RenFontHintingNone   = 1 << 1,
+  RenFontHintingFull   = 2 << 1,
+};
+
 typedef struct { uint8_t b, g, r, a; } RenColor;
 typedef struct { int x, y, width, height; } RenRect;
 
@@ -19,7 +30,7 @@ void ren_get_size(int *x, int *y);
 RenImage* ren_new_image(int width, int height);
 void ren_free_image(RenImage *image);
 
-RenFont* ren_load_font(const char *filename, float size);
+RenFont* ren_load_font(const char *filename, float size, unsigned int renderer_flags);
 void ren_free_font(RenFont *font);
 void ren_set_font_tab_width(RenFont *font, int n);
 int ren_get_font_tab_width(RenFont *font);