From 6a81ec4893cc18c624858871a70e7d6b33388c72 Mon Sep 17 00:00:00 2001
From: Patrick Walton <pcwalton@mimiga.net>
Date: Wed, 20 Dec 2017 10:40:21 -0800
Subject: [PATCH] Make SVG stroke width more accurate, and switch to XCAA by
 default.

Partially addresses #57.
---
 demo/client/html/svg-demo.html.hbs |  4 ++--
 demo/client/src/svg-loader.ts      | 22 ++++++++++++++++------
 path-utils/src/stroke.rs           |  8 +++++---
 3 files changed, 23 insertions(+), 11 deletions(-)

diff --git a/demo/client/html/svg-demo.html.hbs b/demo/client/html/svg-demo.html.hbs
index ee7c431a..d019030c 100644
--- a/demo/client/html/svg-demo.html.hbs
+++ b/demo/client/html/svg-demo.html.hbs
@@ -56,10 +56,10 @@
                                     <select id="pf-aa-level-select" class="form-control custom-select">
                                         <option value="none">None</option>
                                         <option value="ssaa-2">2&times;SSAA</option>
-                                        <option value="ssaa-4" selected>4&times;SSAA</option>
+                                        <option value="ssaa-4">4&times;SSAA</option>
                                         <option value="ssaa-8">8&times;SSAA</option>
                                         <option value="ssaa-16">16&times;SSAA</option>
-                                        <option value="xcaa">XCAA (experimental)</option>
+                                        <option value="xcaa" selected>XCAA</option>
                                     </select>
                                 </div>
                             </form>
diff --git a/demo/client/src/svg-loader.ts b/demo/client/src/svg-loader.ts
index 5e8f0817..016f1b01 100644
--- a/demo/client/src/svg-loader.ts
+++ b/demo/client/src/svg-loader.ts
@@ -15,7 +15,7 @@ import * as _ from 'lodash';
 import 'path-data-polyfill.js';
 import {parseServerTiming, PathfinderMeshData} from "./meshes";
 import {AlphaMaskCompositingOperation, RenderTask, RenderTaskType} from './render-task';
-import {panic, Range, unwrapNull, unwrapUndef} from "./utils";
+import {panic, Range, unwrapNull, unwrapUndef, lerp} from "./utils";
 
 export const BUILTIN_SVG_URI: string = "/svg/demo";
 
@@ -23,9 +23,6 @@ const parseColor = require('parse-color');
 
 const PARTITION_SVG_PATHS_ENDPOINT_URL: string = "/partition-svg-paths";
 
-/// The minimum size of a stroke.
-const HAIRLINE_STROKE_WIDTH: number = 0.25;
-
 declare class SVGPathSegment {
     type: string;
     values: number[];
@@ -62,7 +59,20 @@ export class SVGStroke extends SVGPath {
         super(element, 'stroke');
 
         const style = window.getComputedStyle(element);
-        this.width = parseInt(style.strokeWidth!, 10);
+        const ctm = element.getCTM();
+
+        const strokeWidthString = unwrapNull(style.strokeWidth);
+        const matches = /^(\d+\.?\d*)(.*)$/.exec(strokeWidthString);
+        let strokeWidth;
+        if (matches == null) {
+            strokeWidth = 0.0;
+        } else {
+            strokeWidth = parseFloat(matches[1]);
+            if (matches[2] === 'px')
+                strokeWidth *= lerp(ctm.a, ctm.d, 0.5);
+        }
+
+        this.width = strokeWidth;
     }
 }
 
@@ -179,7 +189,7 @@ export class SVGLoader {
                 this.pathBounds.push(pathBounds);
             } else if (instance instanceof SVGStroke) {
                 this.paths.push({
-                    kind: { Stroke: Math.max(HAIRLINE_STROKE_WIDTH, instance.width) },
+                    kind: { Stroke: instance.width },
                     segments: segments,
                 });
                 this.pathBounds.push(pathBounds);
diff --git a/path-utils/src/stroke.rs b/path-utils/src/stroke.rs
index fce2de99..59cf98ed 100644
--- a/path-utils/src/stroke.rs
+++ b/path-utils/src/stroke.rs
@@ -56,6 +56,8 @@ impl Stroke {
 
     /// TODO(pcwalton): Miter and round joins.
     fn offset_subpath(&self, output: &mut PathBuffer, input: &PathBuffer, subpath_index: u32) {
+        let radius = self.width * 0.5;
+
         let subpath = &input.subpaths[subpath_index as usize];
 
         let mut prev_position = None;
@@ -65,7 +67,7 @@ impl Stroke {
 
             if let Some(ref prev_position) = prev_position {
                 if endpoint.control_point_index == u32::MAX {
-                    let offset_line = Line::new(&prev_position, position).offset(self.width);
+                    let offset_line = Line::new(&prev_position, position).offset(radius);
                     output.endpoints.extend_from_slice(&[
                         Endpoint {
                             position: offset_line.endpoints[0],
@@ -87,9 +89,9 @@ impl Stroke {
                     let control_point_position =
                         &input.control_points[endpoint.control_point_index as usize];
                     let offset_line_0 =
-                        Line::new(&prev_position, control_point_position).offset(self.width);
+                        Line::new(&prev_position, control_point_position).offset(radius);
                     let offset_line_1 =
-                        Line::new(control_point_position, position).offset(self.width);
+                        Line::new(control_point_position, position).offset(radius);
 
                     // FIXME(pcwalton): Can the `None` case ever happen?
                     let offset_control_point =