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, 13 insertions, 5 deletions

diff --git a/src/renderer/mod.rs b/src/renderer/mod.rs
index b84ed1ee..001cb40f 100644
--- a/src/renderer/mod.rs
+++ b/src/renderer/mod.rs
@@ -97,6 +97,7 @@ impl QuadRenderer {
         unsafe {
             // set color
             gl::Uniform3f(self.program.u_color, 1., 1., 0.5);
+            gl::Uniform3f(self.program.u_bg_color, 0.08, 0.08, 0.08);
         }
 
         let rect = get_rect(glyph, x, y);
@@ -134,7 +135,7 @@ impl QuadRenderer {
 
 fn get_rect(glyph: &Glyph, x: f32, y: f32) -> Rect<f32> {
     Rect::new(
-        Point2D::new(x, y),
+        Point2D::new(x + glyph.left as f32, y - (glyph.height - glyph.top) as f32),
         Size2D::new(glyph.width as f32, glyph.height as f32)
     )
 }
@@ -152,6 +153,8 @@ pub struct ShaderProgram {
     u_projection: GLint,
     /// color uniform
     u_color: GLint,
+    /// background color uniform
+    u_bg_color: GLint,
 }
 
 impl ShaderProgram {
@@ -180,11 +183,13 @@ impl ShaderProgram {
         // get uniform locations
         let projection_str = CString::new("projection").unwrap();
         let color_str = CString::new("textColor").unwrap();
+        let bg_color_str = CString::new("bgColor").unwrap();
 
-        let (projection, color) = unsafe {
+        let (projection, color, bg_color) = unsafe {
             (
                 gl::GetUniformLocation(program, projection_str.as_ptr()),
-                gl::GetUniformLocation(program, color_str.as_ptr())
+                gl::GetUniformLocation(program, color_str.as_ptr()),
+                gl::GetUniformLocation(program, bg_color_str.as_ptr()),
             )
         };
 
@@ -192,11 +197,14 @@ impl ShaderProgram {
         assert!(projection != gl::INVALID_OPERATION as i32);
         assert!(color != gl::INVALID_VALUE as i32);
         assert!(color != gl::INVALID_OPERATION as i32);
+        assert!(bg_color != gl::INVALID_VALUE as i32);
+        assert!(bg_color != gl::INVALID_OPERATION as i32);
 
         let shader = ShaderProgram {
             id: program,
             u_projection: projection,
             u_color: color,
+            u_bg_color: bg_color,
         };
 
         // set projection uniform
@@ -287,11 +295,11 @@ impl Glyph {
             gl::TexImage2D(
                 gl::TEXTURE_2D,
                 0,
-                gl::RED as i32,
+                gl::RGB as i32,
                 rasterized.width as i32,
                 rasterized.height as i32,
                 0,
-                gl::RED,
+                gl::RGB,
                 gl::UNSIGNED_BYTE,
                 rasterized.buf.as_ptr() as *const _
             );