add experiemental svg font support

The vertical alignment is wonky, and some glyphs have the wrong
aspect and are missig colors. eg: the watermelon glyph in Noto Color
Emoji (U+1f349).

Turn this off by default, and skip loading fonts that have svg by
default.

config/src/config.rs

@@ -718,6 +718,9 @@ pub struct Config {
     #[dynamic(default)]
     pub experimental_pixel_positioning: bool,
 
+    #[dynamic(default)]
+    pub experimental_svg_fonts: bool,
+
     #[dynamic(default)]
     pub bidi_enabled: bool,
 

config/src/font.rs

@@ -266,6 +266,8 @@ bitflags! {
         const MONOCHROME = 4096;
         /// Disable auto-hinter.
         const NO_AUTOHINT = 32768;
+        const NO_SVG = 16777216;
+        const SVG_ONLY = 8388608;
     }
 }
 
@@ -293,6 +295,12 @@ impl ToString for FreeTypeLoadFlags {
         if self.contains(Self::NO_BITMAP) {
             s.push("NO_BITMAP");
         }
+        if self.contains(Self::NO_SVG) {
+            s.push("NO_SVG");
+        }
+        if self.contains(Self::SVG_ONLY) {
+            s.push("SVG_ONLY");
+        }
         if self.contains(Self::FORCE_AUTOHINT) {
             s.push("FORCE_AUTOHINT");
         }
@@ -317,6 +325,8 @@ impl TryFrom<String> for FreeTypeLoadFlags {
                 "DEFAULT" => flags |= Self::DEFAULT,
                 "NO_HINTING" => flags |= Self::NO_HINTING,
                 "NO_BITMAP" => flags |= Self::NO_BITMAP,
+                "NO_SVG" => flags |= Self::NO_SVG,
+                "SVG_ONLY" => flags |= Self::SVG_ONLY,
                 "FORCE_AUTOHINT" => flags |= Self::FORCE_AUTOHINT,
                 "MONOCHROME" => flags |= Self::MONOCHROME,
                 "NO_AUTOHINT" => flags |= Self::NO_AUTOHINT,

deps/freetype/bindings.h

@@ -8,4 +8,5 @@
 #include <freetype/ftsynth.h>
 #include <freetype/ftglyph.h>
 #include <freetype/ftsnames.h>
+#include <freetype/otsvg.h>
 #include <freetype/ttnameid.h>

deps/freetype/regenerate.sh

@@ -17,7 +17,7 @@ bindgen bindings.h -o src/lib.rs \
   --raw-line "pub type FT_UInt64 = u64;" \
   --default-enum-style rust \
   --generate=functions,types,vars \
-  --allowlist-function="FT_.*" \
-  --allowlist-type="[FT]T_.*" \
-  --allowlist-var="[FT]T_.*" \
+  --allowlist-function="(SVG|FT)_.*" \
+  --allowlist-type="(SVG|[FT]T)_.*" \
+  --allowlist-var="(SVG|[FT]T)_.*" \
   -- -Ifreetype2/include