Revert "don't trust convexity with affine transforms"

This reverts commit 26d8d77.

Reason for revert: speculative, in case this is blocking the chrome roll

Original change's description:
> don't trust convexity with affine transforms
> 
> In theory, a convex shape transformed by an affine matrix should still
> be convex. However, due to numerical nastiness of floats, when we try
> to determine if something is convex, we can get different answers pre
> and post a transformation (think of two line segments nearly colinear).
> 
> Convex paths take a faster scan converter, but it is only well behaved
> if the path is, in fact, convex. Thus we have to be conservative about
> which paths we mark as convex.
> 
> This bug found a case where a "convex" path, after going through a transform,
> became (according to our measure) non-convex. The bug was that we *thought*
> that once convex always convex, but in reality it was not. The fix (hack) is
> to notice when we transform by an affine matrix (we're still assuming/hoping
> that scaling and translate keep things convex (1)...) and mark the convexity
> as "unknown", forcing us to re-compute it.
> 
> This will slow down these paths, since it costs something to compute convexity.
> Hopefully non-scale-translate transforms are rare, so we won't notice the
> speed loss too much.
> 
> (1) This is not proven. If we find scaling/translation to break our notion of
> convexity, we'll need to get more aggressive/clever to find a fix.
> 
> 
> Bug: 899689
> Change-Id: I5921eca247428bf89380bc2395fe373fa70deb1d
> Reviewed-on: https://skia-review.googlesource.com/c/173080
> Commit-Queue: Mike Reed <reed@google.com>
> Reviewed-by: Cary Clark <caryclark@google.com>
> Reviewed-by: Jim Van Verth <jvanverth@google.com>

TBR=mtklein@google.com,jvanverth@google.com,caryclark@google.com,reed@google.com,caryclark@skia.org

Change-Id: I5d846798f2c34c6576591a3c3125cfdc3c72dbdc
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 899689
Reviewed-on: https://skia-review.googlesource.com/c/173162
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>

Author: reed-at-google

src/core/SkPath.cpp

@@ -1841,13 +1841,6 @@ void SkPath::transform(const SkMatrix& matrix, SkPath* dst) const {
             dst->fIsVolatile = fIsVolatile;
         }
 
-        if (!matrix.isScaleTranslate()) {
-            // If we're rotated/skewed/etc. we can't trust that our convexity stays put.
-            // ... just because convexity is fragle with segments are *nearly* colinear...
-            // See Path_crbug_899689 test, which asserts w/o this check.
-            dst->fConvexity = kUnknown_Convexity;
-        }
-
         if (SkPathPriv::kUnknown_FirstDirection == fFirstDirection) {
             dst->fFirstDirection = SkPathPriv::kUnknown_FirstDirection;
         } else {

tests/PathTest.cpp

@@ -5204,66 +5204,3 @@ DEF_TEST(Path_increserve_handle_neg_crbug_883666, r) {
     shallowPath.incReserve(0xffffffff);
 }
 
-DEF_TEST(Path_crbug_899689, r) {
-    SkBitmap bitmap;
-    bitmap.allocN32Pixels(24, 24);
-    SkCanvas canvas(bitmap);
-
-    SkPaint paint;
-    paint.setAntiAlias(true);
-    paint.setStyle(SkPaint::kFill_Style);
-
-    // This is monotone in both x and y, but has a tiny concavity
-    SkPath path;
-    path.moveTo(-1,-1);
-    path.lineTo(0, 0);
-    path.lineTo(0, 0.5e-10f);
-    path.lineTo(0.1e-10f, 1.1e-10f);
-    path.lineTo(1.5e-10f, 1.1e-10f);
-    path.lineTo(1.5e-10f, 2.5e-10f);
-    path.lineTo(0.9f, 1);
-    path.lineTo(-1, 1);
-    path.close();
-
-#if 0
-    // If asked, Skia is going to declare it convex
-    if(path.isConvex()) {
-        printf("convex\n");
-    } else {
-        printf("not convex\n");
-    }
-#endif
-
-    SkMatrix m;
-    m.setRotate(-45);
-    m.postScale(10e10f, 10e10f);
-    m.postSkew(-1, 0);
-    m.postTranslate(1, 10);
-    path.transform(m);
-
-#if 0
-    // The convexity flag is going to survive all affine transforms
-    // Even those that will enlarge the concavity and make the path
-    // non-monotone.
-    // As demonstrated here
-    if(path.isConvex()) {
-        printf("convex\n");
-    } else {
-        printf("not convex\n");
-    }
-
-    // This used to print "convex" (and then assert) before the fix.
-#endif
-
-    // We'll use the path as a clip region
-    canvas.clipPath(path);
-
-    // And now we'll just draw a simple triangle.
-    SkPath path2;
-    path2.moveTo(15.5f, 15);
-    path2.lineTo(50.5f, 50);
-    path2.lineTo(-19.5f, 50);
-    path2.close();
-    canvas.drawPath(path2, paint);
-}
-