path ops work in progress

src/pathops/SkDLineIntersection.cpp

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 #include "SkIntersections.h"
 #include "SkPathOpsLine.h"
 
 /* Determine the intersection point of two lines. This assumes the lines are not parallel,
    and that that the lines are infinite.
    From http://en.wikipedia.org/wiki/Line-line_intersection
  */
 SkDPoint SkIntersections::Line(const SkDLine& a, const SkDLine& b) {
     double axLen = a[1].fX - a[0].fX;
     double ayLen = a[1].fY - a[0].fY;
     double bxLen = b[1].fX - b[0].fX;
     double byLen = b[1].fY - b[0].fY;
     double denom = byLen * axLen - ayLen * bxLen;
     SkASSERT(denom);
     double term1 = a[1].fX * a[0].fY - a[1].fY * a[0].fX;
     double term2 = b[1].fX * b[0].fY - b[1].fY * b[0].fX;
     SkDPoint p;
     p.fX = (term1 * bxLen - axLen * term2) / denom;
     p.fY = (term1 * byLen - ayLen * term2) / denom;
     return p;
 }
 
-int SkIntersections::computePoints(const SkDLine& line, int used) {
+void SkIntersections::cleanUpCoincidence() {
+    SkASSERT(fUsed == 2);
+    // both t values are good
+    bool startMatch = fT[0][0] == 0 && (fT[1][0] == 0 || fT[1][0] == 1);
+    bool endMatch = fT[0][1] == 1 && (fT[1][1] == 0 || fT[1][1] == 1);
+    if (startMatch || endMatch) {
+        removeOne(startMatch);
+        return;
+    }
+    // either t value is good
+    bool pStartMatch = fT[0][0] == 0 || fT[1][0] == 0 || fT[1][0] == 1;
+    bool pEndMatch = fT[0][1] == 1 || fT[1][1] == 0 || fT[1][1] == 1;
+    removeOne(pStartMatch || !pEndMatch);
+}
+
+void SkIntersections::cleanUpParallelLines(bool parallel) {
+    while (fUsed > 2) {
+        removeOne(1);
+    }
+    if (fUsed == 2 && !parallel) {
+        bool startMatch = fT[0][0] == 0 || fT[1][0] == 0 || fT[1][0] == 1;
+        bool endMatch = fT[0][1] == 1 || fT[1][1] == 0 || fT[1][1] == 1;
+        if ((!startMatch && !endMatch) || approximately_equal(fT[0][0], fT[0][1])) {
+            SkASSERT(startMatch || endMatch);
+            removeOne(endMatch);
+        }
+    }
+}
+
+void SkIntersections::computePoints(const SkDLine& line, int used) {
     fPt[0] = line.ptAtT(fT[0][0]);
     if ((fUsed = used) == 2) {
         fPt[1] = line.ptAtT(fT[0][1]);
     }
-    return fUsed;
 }
 
 int SkIntersections::intersectRay(const SkDLine& a, const SkDLine& b) {
+    fMax = 2;
     SkDVector aLen = a[1] - a[0];
     SkDVector bLen = b[1] - b[0];
     /* Slopes match when denom goes to zero:
                       axLen / ayLen ==                   bxLen / byLen
     (ayLen * byLen) * axLen / ayLen == (ayLen * byLen) * bxLen / byLen
              byLen  * axLen         ==  ayLen          * bxLen
              byLen  * axLen         -   ayLen          * bxLen == 0 ( == denom )
      */
     double denom = bLen.fY * aLen.fX - aLen.fY * bLen.fX;
     SkDVector ab0 = a[0] - b[0];
@@ skipping 14 matching lines @@
         */
         if (!AlmostEqualUlps(aLen.fX * a[0].fY - aLen.fY * a[0].fX,
                 aLen.fX * b[0].fY - aLen.fY * b[0].fX)) {
             return fUsed = 0;
         }
         // there's no great answer for intersection points for coincident rays, but return something
         fT[0][0] = fT[1][0] = 0;
         fT[1][0] = fT[1][1] = 1;
         used = 2;
     }
-    return computePoints(a, used);
+    computePoints(a, used);
+    return fUsed;
 }
 
 // note that this only works if both lines are neither horizontal nor vertical
 int SkIntersections::intersect(const SkDLine& a, const SkDLine& b) {
+    fMax = 3;  // note that we clean up so that there is no more than two in the end
     // see if end points intersect the opposite line
     double t;
     for (int iA = 0; iA < 2; ++iA) {
         if ((t = b.exactPoint(a[iA])) >= 0) {
             insert(iA, t, a[iA]);
         }
     }
     for (int iB = 0; iB < 2; ++iB) {
         if ((t = a.exactPoint(b[iB])) >= 0) {
             insert(t, iB, b[iB]);
         }
     }
     /* Determine the intersection point of two line segments
        Return FALSE if the lines don't intersect
        from: http://paulbourke.net/geometry/lineline2d/ */
     double axLen = a[1].fX - a[0].fX;
     double ayLen = a[1].fY - a[0].fY;
     double bxLen = b[1].fX - b[0].fX;
     double byLen = b[1].fY - b[0].fY;
     /* Slopes match when denom goes to zero:
                       axLen / ayLen ==                   bxLen / byLen
     (ayLen * byLen) * axLen / ayLen == (ayLen * byLen) * bxLen / byLen
              byLen  * axLen         ==  ayLen          * bxLen
              byLen  * axLen         -   ayLen          * bxLen == 0 ( == denom )
      */
     double axByLen = axLen * byLen;
     double ayBxLen = ayLen * bxLen;
     // detect parallel lines the same way here and in SkOpAngle operator <
     // so that non-parallel means they are also sortable
-    bool unparallel = NotAlmostEqualUlps(axByLen, ayBxLen);
-    if (unparallel) {
+    bool unparallel = fAllowNear ? NotAlmostEqualUlps(axByLen, ayBxLen)
+            : NotAlmostDequalUlps(axByLen, ayBxLen);
+    if (unparallel && fUsed == 0) {
         double ab0y = a[0].fY - b[0].fY;
         double ab0x = a[0].fX - b[0].fX;
         double numerA = ab0y * bxLen - byLen * ab0x;
         double numerB = ab0y * axLen - ayLen * ab0x;
         double denom = axByLen - ayBxLen;
         if (between(0, numerA, denom) && between(0, numerB, denom)) {
             fT[0][0] = numerA / denom;
             fT[1][0] = numerB / denom;
             computePoints(a, 1);
         }
     }
     if (fAllowNear || !unparallel) {
         for (int iA = 0; iA < 2; ++iA) {
             if ((t = b.nearPoint(a[iA])) >= 0) {
                 insert(iA, t, a[iA]);
             }
         }
         for (int iB = 0; iB < 2; ++iB) {
             if ((t = a.nearPoint(b[iB])) >= 0) {
                 insert(t, iB, b[iB]);
             }
         }
     }
-    while (fUsed > 2) {
-        removeOne(1);
-    }
-    if (fUsed == 2 && unparallel) {
-        bool startMatch = fT[0][0] == 0 || fT[1][0] == 0 || fT[1][0] == 1;
-        bool endMatch = fT[0][1] == 1 || fT[1][1] == 0 || fT[1][1] == 1;
-        if (!startMatch && !endMatch) {
-            SkASSERT(startMatch || endMatch);
-            removeOne(endMatch);
-        }
-    }
+    cleanUpParallelLines(!unparallel);
+    SkASSERT(fUsed <= 2);
     return fUsed;
 }
 
 static int horizontal_coincident(const SkDLine& line, double y) {
     double min = line[0].fY;
     double max = line[1].fY;
     if (min > max) {
         SkTSwap(min, max);
     }
     if (min > y || max < y) {
         return 0;
     }
     if (AlmostEqualUlps(min, max) && max - min < fabs(line[0].fX - line[1].fX)) {
         return 2;
     }
     return 1;
 }
 
 static double horizontal_intercept(const SkDLine& line, double y) {
      return (y - line[0].fY) / (line[1].fY - line[0].fY);
 }
 
 int SkIntersections::horizontal(const SkDLine& line, double y) {
+    fMax = 2;
     int horizontalType = horizontal_coincident(line, y);
     if (horizontalType == 1) {
         fT[0][0] = horizontal_intercept(line, y);
     } else if (horizontalType == 2) {
         fT[0][0] = 0;
         fT[0][1] = 1;
     }
     return fUsed = horizontalType;
 }
 
 int SkIntersections::horizontal(const SkDLine& line, double left, double right,
                                 double y, bool flipped) {
+    fMax = 2;
     // see if end points intersect the opposite line
     double t;
     const SkDPoint leftPt = { left, y };
     if ((t = line.exactPoint(leftPt)) >= 0) {
         insert(t, (double) flipped, leftPt);
     }
     if (left != right) {
         const SkDPoint rightPt = { right, y };
         if ((t = line.exactPoint(rightPt)) >= 0) {
             insert(t, (double) !flipped, rightPt);
         }
         for (int index = 0; index < 2; ++index) {
             if ((t = SkDLine::ExactPointH(line[index], left, right, y)) >= 0) {
                 insert((double) index, flipped ? 1 - t : t, line[index]);
             }
         }
     }
     int result = horizontal_coincident(line, y);
     if (result == 1 && fUsed == 0) {
         fT[0][0] = horizontal_intercept(line, y);
         double xIntercept = line[0].fX + fT[0][0] * (line[1].fX - line[0].fX);
         if (between(left, xIntercept, right)) {
             fT[1][0] = (xIntercept - left) / (right - left);
             if (flipped) {
                 // OPTIMIZATION: ? instead of swapping, pass original line, use [1].fX - [0].fX
                 for (int index = 0; index < result; ++index) {
                     fT[1][index] = 1 - fT[1][index];
                 }
             }
-            return computePoints(line, result);
+            computePoints(line, result);
         }
     }
-    if (!fAllowNear && result != 2) {
-        return fUsed;
-    }
-    if ((t = line.nearPoint(leftPt)) >= 0) {
-        insert(t, (double) flipped, leftPt);
-    }
-    if (left != right) {
-        const SkDPoint rightPt = { right, y };
-        if ((t = line.nearPoint(rightPt)) >= 0) {
-            insert(t, (double) !flipped, rightPt);
+    if (fAllowNear || result == 2) {
+        if ((t = line.nearPoint(leftPt)) >= 0) {
+            insert(t, (double) flipped, leftPt);
         }
-        for (int index = 0; index < 2; ++index) {
-            if ((t = SkDLine::NearPointH(line[index], left, right, y)) >= 0) {
-                insert((double) index, flipped ? 1 - t : t, line[index]);
+        if (left != right) {
+            const SkDPoint rightPt = { right, y };
+            if ((t = line.nearPoint(rightPt)) >= 0) {
+                insert(t, (double) !flipped, rightPt);
+            }
+            for (int index = 0; index < 2; ++index) {
+                if ((t = SkDLine::NearPointH(line[index], left, right, y)) >= 0) {
+                    insert((double) index, flipped ? 1 - t : t, line[index]);
+                }
             }
         }
     }
+    cleanUpParallelLines(result == 2);
     return fUsed;
 }
 
 static int vertical_coincident(const SkDLine& line, double x) {
     double min = line[0].fX;
     double max = line[1].fX;
     if (min > max) {
         SkTSwap(min, max);
     }
     if (!precisely_between(min, x, max)) {
         return 0;
     }
     if (AlmostEqualUlps(min, max)) {
         return 2;
     }
     return 1;
 }
 
 static double vertical_intercept(const SkDLine& line, double x) {
     return (x - line[0].fX) / (line[1].fX - line[0].fX);
 }
 
 int SkIntersections::vertical(const SkDLine& line, double x) {
+    fMax = 2;
     int verticalType = vertical_coincident(line, x);
     if (verticalType == 1) {
         fT[0][0] = vertical_intercept(line, x);
     } else if (verticalType == 2) {
         fT[0][0] = 0;
         fT[0][1] = 1;
     }
     return fUsed = verticalType;
 }
 
 int SkIntersections::vertical(const SkDLine& line, double top, double bottom,
                               double x, bool flipped) {
+    fMax = 2;
     // see if end points intersect the opposite line
     double t;
     SkDPoint topPt = { x, top };
     if ((t = line.exactPoint(topPt)) >= 0) {
         insert(t, (double) flipped, topPt);
     }
     if (top != bottom) {
         SkDPoint bottomPt = { x, bottom };
         if ((t = line.exactPoint(bottomPt)) >= 0) {
             insert(t, (double) !flipped, bottomPt);
         }
         for (int index = 0; index < 2; ++index) {
             if ((t = SkDLine::ExactPointV(line[index], top, bottom, x)) >= 0) {
                 insert((double) index, flipped ? 1 - t : t, line[index]);
             }
         }
     }
     int result = vertical_coincident(line, x);
     if (result == 1 && fUsed == 0) {
         fT[0][0] = vertical_intercept(line, x);
         double yIntercept = line[0].fY + fT[0][0] * (line[1].fY - line[0].fY);
         if (between(top, yIntercept, bottom)) {
             fT[1][0] = (yIntercept - top) / (bottom - top);
             if (flipped) {
                 // OPTIMIZATION: instead of swapping, pass original line, use [1].fY - [0].fY
                 for (int index = 0; index < result; ++index) {
                     fT[1][index] = 1 - fT[1][index];
                 }
             }
-            return computePoints(line, result);
+            computePoints(line, result);
         }
     }
-    if (!fAllowNear && result != 2) {
-        return fUsed;
-    }
-    if ((t = line.nearPoint(topPt)) >= 0) {
-        insert(t, (double) flipped, topPt);
-    }
-    if (top != bottom) {
-        SkDPoint bottomPt = { x, bottom };
-        if ((t = line.nearPoint(bottomPt)) >= 0) {
-            insert(t, (double) !flipped, bottomPt);
+    if (fAllowNear || result == 2) {
+        if ((t = line.nearPoint(topPt)) >= 0) {
+            insert(t, (double) flipped, topPt);
         }
-        for (int index = 0; index < 2; ++index) {
-            if ((t = SkDLine::NearPointV(line[index], top, bottom, x)) >= 0) {
-                insert((double) index, flipped ? 1 - t : t, line[index]);
+        if (top != bottom) {
+            SkDPoint bottomPt = { x, bottom };
+            if ((t = line.nearPoint(bottomPt)) >= 0) {
+                insert(t, (double) !flipped, bottomPt);
+            }
+            for (int index = 0; index < 2; ++index) {
+                if ((t = SkDLine::NearPointV(line[index], top, bottom, x)) >= 0) {
+                    insert((double) index, flipped ? 1 - t : t, line[index]);
+                }
             }
         }
     }
+    cleanUpParallelLines(result == 2);
     return fUsed;
 }
 
 // from http://www.bryceboe.com/wordpress/wp-content/uploads/2006/10/intersect.py
 // 4 subs, 2 muls, 1 cmp
 static bool ccw(const SkDPoint& A, const SkDPoint& B, const SkDPoint& C) {
     return (C.fY - A.fY) * (B.fX - A.fX) > (B.fY - A.fY) * (C.fX - A.fX);
 }
 
 // 16 subs, 8 muls, 6 cmps
 bool SkIntersections::Test(const SkDLine& a, const SkDLine& b) {
     return ccw(a[0], b[0], b[1]) != ccw(a[1], b[0], b[1])
             && ccw(a[0], a[1], b[0]) != ccw(a[0], a[1], b[1]);
 }