Correct sub-pixel font rendering with OpenGL

Uses the GL_ARB_blend_func_extended to get single-pass, per-channel
alpha blending. gl_generator is now used instead of gl to enable the
extension.

The background color is removed since that presumably needs to run in a
separate pass.

3 files changed, 14 insertions, 17 deletions

diff --git a/src/main.rs b/src/main.rs
index 48aaf11b..ef025bea 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -2,7 +2,6 @@ extern crate fontconfig;
 extern crate freetype;
 extern crate libc;
 extern crate glutin;
-extern crate gl;
 extern crate cgmath;
 extern crate euclid;
 
@@ -17,6 +16,10 @@ use renderer::{Glyph, QuadRenderer};
 use text::FontDesc;
 use grid::Grid;
 
+mod gl {
+    include!(concat!(env!("OUT_DIR"), "/gl_bindings.rs"));
+}
+
 static INIT_LIST: &'static str = "abcdefghijklmnopqrstuvwxyz\
                                   ABCDEFGHIJKLMNOPQRSTUVWXYZ\
                                   01234567890\
@@ -37,7 +40,7 @@ fn main() {
     let (dpi_x, dpi_y) = window.get_dpi().unwrap();
     let dpr = window.hidpi_factor();
 
-    let font_size = 11.0;
+    let font_size = 11.;
 
     let sep_x = 2;
     let sep_y = 5;
@@ -92,8 +95,8 @@ fn main() {
     }
 
     unsafe {
-        // gl::Enable(gl::BLEND);
-        // gl::BlendFunc(gl::SRC_ALPHA, gl::ONE_MINUS_SRC_ALPHA);
+        gl::Enable(gl::BLEND);
+        gl::BlendFunc(gl::SRC1_COLOR, gl::ONE_MINUS_SRC1_COLOR);
         gl::Enable(gl::MULTISAMPLE);
     }
 
@@ -101,7 +104,7 @@ fn main() {
 
     for event in window.wait_events() {
         unsafe {
-            gl::ClearColor(0.08, 0.08, 0.08, 1.0);
+            gl::ClearColor(0.0, 0.0, 0.00, 1.0);
             gl::Clear(gl::COLOR_BUFFER_BIT);
         }
 
diff --git a/src/renderer/mod.rs b/src/renderer/mod.rs
index 001cb40f..4666981b 100644
--- a/src/renderer/mod.rs
+++ b/src/renderer/mod.rs
@@ -96,8 +96,7 @@ impl QuadRenderer {
         self.program.activate();
         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);
+            gl::Uniform3f(self.program.u_color, 0.917, 0.917, 0.917);
         }
 
         let rect = get_rect(glyph, x, y);
@@ -153,8 +152,6 @@ pub struct ShaderProgram {
     u_projection: GLint,
     /// color uniform
     u_color: GLint,
-    /// background color uniform
-    u_bg_color: GLint,
 }
 
 impl ShaderProgram {
@@ -183,13 +180,11 @@ 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, bg_color) = unsafe {
+        let (projection, color) = unsafe {
             (
                 gl::GetUniformLocation(program, projection_str.as_ptr()),
                 gl::GetUniformLocation(program, color_str.as_ptr()),
-                gl::GetUniformLocation(program, bg_color_str.as_ptr()),
             )
         };
 
@@ -197,14 +192,11 @@ 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
diff --git a/src/text.rs b/src/text.rs
index ca414342..0eb08606 100644
--- a/src/text.rs
+++ b/src/text.rs
@@ -91,8 +91,10 @@ impl Rasterizer {
         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!
+        unsafe {
+            let ft_lib = self.library.raw();
+            freetype::ffi::FT_Library_SetLcdFilter(ft_lib, freetype::ffi::FT_LCD_FILTER_LIGHT);
+        }
 
         let bitmap = glyph.bitmap();
         let buf = bitmap.buffer();