give up on big cubics (for now) and just draw a line

BUG=683631, skia:6152

Change-Id: I69aa741af74a37e1d7bed25ad0401535599f6af0
Reviewed-on: https://skia-review.googlesource.com/7659
Reviewed-by: Cary Clark <caryclark@google.com>
Commit-Queue: Mike Reed <reed@google.com>

2 files changed, 37 insertions, 18 deletions

diff --git a/src/core/SkEdgeClipper.cpp b/src/core/SkEdgeClipper.cpp
index 97d716986b..2abbd1b1d4 100644
--- a/src/core/SkEdgeClipper.cpp
+++ b/src/core/SkEdgeClipper.cpp
@@ -391,28 +391,49 @@ void SkEdgeClipper::clipMonoCubic(const SkPoint src[4], const SkRect& clip) {
     }
 }
 
-static bool quick_reject_in_y(const SkPoint pts[4], const SkRect& clip) {
-    Sk4s ys(pts[0].fY, pts[1].fY, pts[2].fY, pts[3].fY);
-    Sk4s t(clip.top());
-    Sk4s b(clip.bottom());
+static SkRect compute_cubic_bounds(const SkPoint pts[4]) {
+    SkRect r;
+    r.set(pts, 4);
+    return r;
+}
 
-    return (ys < t).allTrue() || (ys > b).allTrue();
+static bool too_big_for_reliable_float_math(const SkRect& r) {
+    // limit set as the largest float value for which we can still reliably compute things like
+    // - chopping at XY extrema
+    // - chopping at Y or X values for clipping
+    //
+    // Current value chosen just by experiment. Larger (and still succeeds) is always better.
+    //
+    const SkScalar limit = 1 << 22;
+    return r.fLeft < -limit || r.fTop < -limit || r.fRight > limit || r.fBottom > limit;
 }
 
 bool SkEdgeClipper::clipCubic(const SkPoint srcPts[4], const SkRect& clip) {
     fCurrPoint = fPoints;
     fCurrVerb = fVerbs;
 
-    if (!quick_reject_in_y(srcPts, clip)) {
-        SkPoint monoY[10];
-        int countY = SkChopCubicAtYExtrema(srcPts, monoY);
-        for (int y = 0; y <= countY; y++) {
-            SkPoint monoX[10];
-            int countX = SkChopCubicAtXExtrema(&monoY[y * 3], monoX);
-            for (int x = 0; x <= countX; x++) {
-                this->clipMonoCubic(&monoX[x * 3], clip);
-                SkASSERT(fCurrVerb - fVerbs < kMaxVerbs);
-                SkASSERT(fCurrPoint - fPoints <= kMaxPoints);
+    const SkRect bounds = compute_cubic_bounds(srcPts);
+    // check if we're clipped out vertically
+    if (bounds.fBottom > clip.fTop && bounds.fTop < clip.fBottom) {
+        if (too_big_for_reliable_float_math(bounds)) {
+            // can't safely clip the cubic, so we give up and draw a line (which we can safely clip)
+            //
+            // If we rewrote chopcubicat*extrema and chopmonocubic using doubles, we could very
+            // likely always handle the cubic safely, but (it seems) at a big loss in speed, so
+            // we'd only want to take that alternate impl if needed. Perhaps a TODO to try it.
+            //
+            return this->clipLine(srcPts[0], srcPts[3], clip);
+        } else {
+            SkPoint monoY[10];
+            int countY = SkChopCubicAtYExtrema(srcPts, monoY);
+            for (int y = 0; y <= countY; y++) {
+                SkPoint monoX[10];
+                int countX = SkChopCubicAtXExtrema(&monoY[y * 3], monoX);
+                for (int x = 0; x <= countX; x++) {
+                    this->clipMonoCubic(&monoX[x * 3], clip);
+                    SkASSERT(fCurrVerb - fVerbs < kMaxVerbs);
+                    SkASSERT(fCurrPoint - fPoints <= kMaxPoints);
+                }
             }
         }
     }
diff --git a/tests/PathTest.cpp b/tests/PathTest.cpp
index 3ddacb0164..7515d3e261 100644
--- a/tests/PathTest.cpp
+++ b/tests/PathTest.cpp
@@ -4510,9 +4510,7 @@ DEF_TEST(PathBigCubic, reporter) {
     path.moveTo(0, 512);
 
     // this call should not assert
-    if (false) {
-        SkSurface::MakeRasterN32Premul(255, 255, nullptr)->getCanvas()->drawPath(path, SkPaint());
-    }
+    SkSurface::MakeRasterN32Premul(255, 255, nullptr)->getCanvas()->drawPath(path, SkPaint());
 }
 
 DEF_TEST(PathContains, reporter) {