add support for capped hairlines

src/core/SkScan_Hairline.cpp

 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkScan.h"
 #include "SkBlitter.h"
 #include "SkRasterClip.h"
@@ skipping 330 matching lines @@
      than a pixel.
      */
     int level = (33 - SkCLZ(d)) >> 1;
     // sanity check on level (from the previous version)
     if (level > kMaxQuadSubdivideLevel) {
         level = kMaxQuadSubdivideLevel;
     }
     return level;
 }
 
-static void hair_path(const SkPath& path, const SkRasterClip& rclip, SkBlitter* blitter,
+/* Extend the points in the direction of the starting or ending tangent by 1/2 unit to
+   account for a round or square cap. If there's no distance between the end point and
+   the control point, use the next control point to create a tangent. If the curve
+   is degenerate, move the cap out 1/2 unit horizontally. */
+template <SkPaint::Cap capStyle>
+void extend_pts(SkPath::Verb prevVerb, SkPath::Verb nextVerb, SkPoint* pts, int ptCount) {
+    const SkScalar capOutset = SkPaint::kSquare_Cap == capStyle ? 0.5f : SK_ScalarPI / 8;

[reed1, 2015/12/08 16:59:02]

1. assert that the capStyle is either Square or Round?
2. document why PI/8 for round?

[caryclark, 2015/12/08 19:59:39]

Done.

+    if (SkPath::kMove_Verb == prevVerb) {
+        SkPoint* first = pts;
+        SkPoint* ctrl = first;
+        int controls = ptCount - 1;
+        SkVector tangent;
+        do {
+            tangent = *first - *++ctrl;
+        } while (tangent.isZero() && --controls > 0);
+        if (tangent.isZero()) {
+            tangent.set(1, 0);
+        } else {
+            tangent.normalize();
+        }
+        first->fX += tangent.fX * capOutset;
+        first->fY += tangent.fY * capOutset;
+    }
+    if (SkPath::kMove_Verb == nextVerb || SkPath::kDone_Verb == nextVerb) {
+        SkPoint* last = &pts[ptCount - 1];
+        SkPoint* ctrl = last;
+        int controls = ptCount - 1;
+        SkVector tangent;
+        do {
+            tangent = *last - *--ctrl;
+        } while (tangent.isZero() && --controls > 0);
+        if (tangent.isZero()) {
+            tangent.set(-1, 0);
+        } else {
+            tangent.normalize();
+        }
+        last->fX += tangent.fX * capOutset;
+        last->fY += tangent.fY * capOutset;
+    }
+}
+
+template <SkPaint::Cap capStyle>
+void hair_path(const SkPath& path, const SkRasterClip& rclip, SkBlitter* blitter,
                       SkScan::HairRgnProc lineproc) {
     if (path.isEmpty()) {
         return;
     }
 
     SkAAClipBlitterWrapper wrap;
     const SkRegion* clip = nullptr;
 
     {
         const SkIRect ibounds = path.getBounds().roundOut().makeOutset(1, 1);
 
         if (rclip.quickReject(ibounds)) {
             return;
         }
         if (!rclip.quickContains(ibounds)) {
             if (rclip.isBW()) {
                 clip = &rclip.bwRgn();
             } else {
                 wrap.init(rclip, blitter);
                 blitter = wrap.getBlitter();
                 clip = &wrap.getRgn();
             }
         }
     }
 
     SkPath::RawIter     iter(path);
     SkPoint             pts[4], firstPt, lastPt;
-    SkPath::Verb        verb;
+    SkPath::Verb        verb, prevVerb;
     SkAutoConicToQuads  converter;
 
+    if (SkPaint::kButt_Cap != capStyle) {
+        prevVerb = SkPath::kDone_Verb;
+    }
     while ((verb = iter.next(pts)) != SkPath::kDone_Verb) {
         switch (verb) {
             case SkPath::kMove_Verb:
                 firstPt = lastPt = pts[0];
                 break;
             case SkPath::kLine_Verb:
+                if (SkPaint::kButt_Cap != capStyle) {
+                    extend_pts<capStyle>(prevVerb, iter.peek(), pts, 2);
+                }
                 lineproc(pts, 2, clip, blitter);
                 lastPt = pts[1];
                 break;
             case SkPath::kQuad_Verb:
+                if (SkPaint::kButt_Cap != capStyle) {
+                    extend_pts<capStyle>(prevVerb, iter.peek(), pts, 3);
+                }
                 hairquad(pts, clip, blitter, compute_quad_level(pts), lineproc);
                 lastPt = pts[2];
                 break;
             case SkPath::kConic_Verb: {
+                if (SkPaint::kButt_Cap != capStyle) {
+                    extend_pts<capStyle>(prevVerb, iter.peek(), pts, 3);
+                }
                 // how close should the quads be to the original conic?
                 const SkScalar tol = SK_Scalar1 / 4;
                 const SkPoint* quadPts = converter.computeQuads(pts,
                                                        iter.conicWeight(), tol);
                 for (int i = 0; i < converter.countQuads(); ++i) {
                     int level = compute_quad_level(quadPts);
                     hairquad(quadPts, clip, blitter, level, lineproc);
                     quadPts += 2;
                 }
                 lastPt = pts[2];
                 break;
             }
             case SkPath::kCubic_Verb: {
+                if (SkPaint::kButt_Cap != capStyle) {
+                    extend_pts<capStyle>(prevVerb, iter.peek(), pts, 4);
+                }
                 haircubic(pts, clip, blitter, kMaxCubicSubdivideLevel, lineproc);
                 lastPt = pts[3];
             } break;
             case SkPath::kClose_Verb:
                 pts[0] = lastPt;
                 pts[1] = firstPt;
                 lineproc(pts, 2, clip, blitter);
                 break;
             case SkPath::kDone_Verb:
                 break;
         }
+        if (SkPaint::kButt_Cap != capStyle) {
+            prevVerb = verb;
+        }
     }
 }
 
 void SkScan::HairPath(const SkPath& path, const SkRasterClip& clip, SkBlitter* blitter) {
-    hair_path(path, clip, blitter, SkScan::HairLineRgn);
+    hair_path<SkPaint::kButt_Cap>(path, clip, blitter, SkScan::HairLineRgn);
 }
 
 void SkScan::AntiHairPath(const SkPath& path, const SkRasterClip& clip, SkBlitter* blitter) {
-    hair_path(path, clip, blitter, SkScan::AntiHairLineRgn);
+    hair_path<SkPaint::kButt_Cap>(path, clip, blitter, SkScan::AntiHairLineRgn);
+}
+
+void SkScan::HairSquarePath(const SkPath& path, const SkRasterClip& clip, SkBlitter* blitter) {
+    hair_path<SkPaint::kSquare_Cap>(path, clip, blitter, SkScan::HairLineRgn);
+}
+
+void SkScan::AntiHairSquarePath(const SkPath& path, const SkRasterClip& clip, SkBlitter* blitter) {
+    hair_path<SkPaint::kSquare_Cap>(path, clip, blitter, SkScan::AntiHairLineRgn);
+}
+
+void SkScan::HairRoundPath(const SkPath& path, const SkRasterClip& clip, SkBlitter* blitter) {
+    hair_path<SkPaint::kRound_Cap>(path, clip, blitter, SkScan::HairLineRgn);
+}
+
+void SkScan::AntiHairRoundPath(const SkPath& path, const SkRasterClip& clip, SkBlitter* blitter) {
+    hair_path<SkPaint::kRound_Cap>(path, clip, blitter, SkScan::AntiHairLineRgn);
 }
 
 ///////////////////////////////////////////////////////////////////////////////
 
 void SkScan::FrameRect(const SkRect& r, const SkPoint& strokeSize,
                        const SkRasterClip& clip, SkBlitter* blitter) {
     SkASSERT(strokeSize.fX >= 0 && strokeSize.fY >= 0);
 
     if (strokeSize.fX < 0 || strokeSize.fY < 0) {
         return;
@@ skipping 59 matching lines @@
 
         SkAAClipBlitterWrapper wrap;
         if (!clip.quickContains(r.roundOut().makeOutset(1, 1))) {
             wrap.init(clip, blitter);
             blitter = wrap.getBlitter();
             clipRgn = &wrap.getRgn();
         }
         AntiHairLineRgn(pts, count, clipRgn, blitter);
     }
 }