From b60275e5ea6d8d16b4a5d0ff62ea834d3e598b88 Mon Sep 17 00:00:00 2001
From: Patrick Walton <pcwalton@mimiga.net>
Date: Tue, 6 Mar 2018 13:09:51 -0800
Subject: [PATCH] Convert cubic curves to quadratic ones in fonts

---
 demo/server/src/main.rs                       | 15 ++--
 path-utils/src/cubic_to_quadratic.rs          | 68 +++++++++++++++++++
 .../gles2/xcaa-mono-subpixel-resolve.fs.glsl  |  2 +-
 3 files changed, 80 insertions(+), 5 deletions(-)

diff --git a/demo/server/src/main.rs b/demo/server/src/main.rs
index de0bf7a3..445fd33e 100644
--- a/demo/server/src/main.rs
+++ b/demo/server/src/main.rs
@@ -48,6 +48,7 @@ use pathfinder_font_renderer::{GlyphKey, SubpixelOffset};
 use pathfinder_partitioner::FillRule;
 use pathfinder_partitioner::mesh_library::MeshLibrary;
 use pathfinder_partitioner::partitioner::Partitioner;
+use pathfinder_path_utils::cubic_to_quadratic::CubicToQuadraticTransformer;
 use pathfinder_path_utils::stroke::{StrokeStyle, StrokeToFillIter};
 use pathfinder_path_utils::transform::Transform2DPathIter;
 use rocket::http::{ContentType, Header, Status};
@@ -76,6 +77,8 @@ const SUGGESTED_JSON_SIZE_LIMIT: u64 = 32 * 1024 * 1024;
 
 const MESH_LIBRARY_CACHE_SIZE: usize = 16;
 
+const CUBIC_TO_QUADRATIC_APPROX_TOLERANCE: f32 = 1.0;
+
 static NEXT_FONT_KEY: AtomicUsize = ATOMIC_USIZE_INIT;
 
 lazy_static! {
@@ -486,10 +489,14 @@ fn partition_font(request: Json<PartitionFontRequest>) -> Result<PartitionRespon
     // Partition the decoded glyph outlines.
     let mut library = MeshLibrary::new();
     for (stored_path_index, path_descriptor) in path_descriptors.iter().enumerate() {
-        library.push_stencil_segments((path_descriptor.path_index + 1) as u16,
-                                      PathIter::new(paths[stored_path_index].iter().cloned()));
-        library.push_stencil_normals((path_descriptor.path_index + 1) as u16,
-                                     paths[stored_path_index].iter().cloned());
+        library.push_stencil_segments(
+            (path_descriptor.path_index + 1) as u16,
+            CubicToQuadraticTransformer::new(paths[stored_path_index].iter().cloned(),
+                                             CUBIC_TO_QUADRATIC_APPROX_TOLERANCE));
+        library.push_stencil_normals(
+            (path_descriptor.path_index + 1) as u16,
+            CubicToQuadraticTransformer::new(paths[stored_path_index].iter().cloned(),
+                                             CUBIC_TO_QUADRATIC_APPROX_TOLERANCE));
     }
 
     let mut partitioner = Partitioner::new(library);
diff --git a/path-utils/src/cubic_to_quadratic.rs b/path-utils/src/cubic_to_quadratic.rs
index 79e1430c..daf23ad9 100644
--- a/path-utils/src/cubic_to_quadratic.rs
+++ b/path-utils/src/cubic_to_quadratic.rs
@@ -10,7 +10,9 @@
 
 //! A version of Lyon's `cubic_to_quadratic` that is less sensitive to floating point error.
 
+use euclid::Point2D;
 use lyon_geom::{CubicBezierSegment, QuadraticBezierSegment};
+use lyon_path::PathEvent;
 
 const MAX_APPROXIMATION_ITERATIONS: u8 = 32;
 
@@ -67,3 +69,69 @@ impl Iterator for CubicToQuadraticSegmentIter {
         })
     }
 }
+
+pub struct CubicToQuadraticTransformer<I> where I: Iterator<Item = PathEvent> {
+    inner: I,
+    segment_iter: Option<CubicToQuadraticSegmentIter>,
+    last_point: Point2D<f32>,
+    error_bound: f32,
+}
+
+impl<I> CubicToQuadraticTransformer<I> where I: Iterator<Item = PathEvent> {
+    #[inline]
+    pub fn new(inner: I, error_bound: f32) -> CubicToQuadraticTransformer<I> {
+        CubicToQuadraticTransformer {
+            inner: inner,
+            segment_iter: None,
+            last_point: Point2D::zero(),
+            error_bound: error_bound,
+        }
+    }
+}
+
+impl<I> Iterator for CubicToQuadraticTransformer<I> where I: Iterator<Item = PathEvent> {
+    type Item = PathEvent;
+
+    fn next(&mut self) -> Option<PathEvent> {
+        if let Some(ref mut segment_iter) = self.segment_iter {
+            if let Some(quadratic) = segment_iter.next() {
+                return Some(PathEvent::QuadraticTo(quadratic.ctrl, quadratic.to))
+            }
+        }
+
+        self.segment_iter = None;
+
+        match self.inner.next() {
+            None => None,
+            Some(PathEvent::CubicTo(ctrl1, ctrl2, to)) => {
+                let cubic = CubicBezierSegment {
+                    from: self.last_point,
+                    ctrl1: ctrl1,
+                    ctrl2: ctrl2,
+                    to: to,
+                };
+                self.last_point = to;
+                self.segment_iter = Some(CubicToQuadraticSegmentIter::new(&cubic,
+                                                                          self.error_bound));
+                self.next()
+            }
+            Some(PathEvent::MoveTo(to)) => {
+                self.last_point = to;
+                Some(PathEvent::MoveTo(to))
+            }
+            Some(PathEvent::LineTo(to)) => {
+                self.last_point = to;
+                Some(PathEvent::LineTo(to))
+            }
+            Some(PathEvent::QuadraticTo(ctrl, to)) => {
+                self.last_point = to;
+                Some(PathEvent::QuadraticTo(ctrl, to))
+            }
+            Some(PathEvent::Close) => Some(PathEvent::Close),
+            Some(PathEvent::Arc(to, vector, angle_from, angle_to)) => {
+                self.last_point = to;
+                Some(PathEvent::Arc(to, vector, angle_from, angle_to))
+            }
+        }
+    }
+}
diff --git a/shaders/gles2/xcaa-mono-subpixel-resolve.fs.glsl b/shaders/gles2/xcaa-mono-subpixel-resolve.fs.glsl
index f567eb26..70973020 100644
--- a/shaders/gles2/xcaa-mono-subpixel-resolve.fs.glsl
+++ b/shaders/gles2/xcaa-mono-subpixel-resolve.fs.glsl
@@ -26,7 +26,7 @@ uniform ivec2 uAAAlphaDimensions;
 varying vec2 vTexCoord;
 
 float sampleSource(float deltaX) {
-    return texture2D(uAAAlpha, vec2(vTexCoord.s + deltaX, vTexCoord.y)).r;
+    return abs(texture2D(uAAAlpha, vec2(vTexCoord.s + deltaX, vTexCoord.y)).r);
 }
 
 void main() {