Use subpixel font rendering

OpenGL only supports shared alpha blending. Subpixel font rendering
requires using the font RGB values as alpha masks for the corresponding
RGB channels. To support this, blending is implemented in the fragment
shader.

1 files changed, 18 insertions, 3 deletions

diff --git a/src/text.rs b/src/text.rs
index ea0df76a..ca414342 100644
--- a/src/text.rs
+++ b/src/text.rs
@@ -87,15 +87,30 @@ impl Rasterizer {
     pub fn get_glyph(&mut self, desc: &FontDesc, size: f32, c: char) -> RasterizedGlyph {
         let face = self.get_face(desc).expect("TODO handle get_face error");
         face.set_char_size(to_freetype_26_6(size * self.dpr), 0, self.dpi_x, self.dpi_y).unwrap();
-        face.load_char(c as usize, freetype::face::RENDER).unwrap();
+        face.load_char(c as usize, freetype::face::TARGET_LIGHT).unwrap();
         let glyph = face.glyph();
+        glyph.render_glyph(freetype::render_mode::RenderMode::Lcd).unwrap();
+
+        // FIXME need LCD filtering to reduce color fringes with subpixel rendering. The freetype
+        // bindings don't currently expose this!
+
+        let bitmap = glyph.bitmap();
+        let buf = bitmap.buffer();
+        let pitch = bitmap.pitch() as usize;
+
+        let mut packed = Vec::with_capacity((bitmap.rows() * bitmap.width()) as usize);
+        for i in 0..bitmap.rows() {
+            let start = (i as usize) * pitch;
+            let stop = start + bitmap.width() as usize;
+            packed.extend_from_slice(&buf[start..stop]);
+        }
 
         RasterizedGlyph {
             top: glyph.bitmap_top() as usize,
             left: glyph.bitmap_left() as usize,
-            width: glyph.bitmap().width() as usize,
+            width: glyph.bitmap().width() as usize / 3,
             height: glyph.bitmap().rows() as usize,
-            buf: glyph.bitmap().buffer().to_vec(),
+            buf: packed,
         }
     }
 }