Apply hairline optimization only if the path renderer wants it

Make the decision to convert thin, non-hairline paths to hairline
paths at the renderer level.

The current nv_path_rendering implementation does not render
hairlines. Rendering the hairlines with normal renderers cause
unneccessary gl program changes, which is quite slow.

Changes the behavior of non-nv_path_rendering paths to always perform
the optimization if the shape ends up being painted by a renderer that
wants the optimization. Previously the optimization was applied only
when callgraph started with SkCanvas::drawPath.

Applies the optimization for GrAAHairLineRenderer and
GrDefaultPathRenderer.

This changes gm results for dashing3_{msaa4,gpu} and drawlooper_msaa4.

R=bsalomon@google.com, jvanverth@google.com, rmistry@google.com

Author: kkinnunen@nvidia.com

Review URL: https://codereview.chromium.org/38573007

git-svn-id: http://skia.googlecode.com/svn/trunk@12357 2bbb7eff-a529-9590-31e7-b0007b416f81

1 files changed, 7 insertions, 18 deletions

diff --git a/src/core/SkDraw.cpp b/src/core/SkDraw.cpp
index 0288dee409..52891ea521 100644
--- a/src/core/SkDraw.cpp
+++ b/src/core/SkDraw.cpp
@@ -988,24 +988,11 @@ static bool xfermodeSupportsCoverageAsAlpha(SkXfermode* xfer) {
     }
 }
 
-bool SkDrawTreatAsHairline(const SkPaint& paint, const SkMatrix& matrix,
-                           SkScalar* coverage) {
-    SkASSERT(coverage);
-    if (SkPaint::kStroke_Style != paint.getStyle()) {
-        return false;
-    }
-    SkScalar strokeWidth = paint.getStrokeWidth();
-    if (0 == strokeWidth) {
-        *coverage = SK_Scalar1;
-        return true;
-    }
+bool SkDrawTreatAAStrokeAsHairline(SkScalar strokeWidth, const SkMatrix& matrix,
+                                   SkScalar* coverage) {
+    SkASSERT(strokeWidth > 0);
+    // We need to try to fake a thick-stroke with a modulated hairline.
 
-    // if we get here, we need to try to fake a thick-stroke with a modulated
-    // hairline
-
-    if (!paint.isAntiAlias()) {
-        return false;
-    }
     if (matrix.hasPerspective()) {
         return false;
     }
@@ -1017,7 +1004,9 @@ bool SkDrawTreatAsHairline(const SkPaint& paint, const SkMatrix& matrix,
     SkScalar len0 = fast_len(dst[0]);
     SkScalar len1 = fast_len(dst[1]);
     if (len0 <= SK_Scalar1 && len1 <= SK_Scalar1) {
-        *coverage = SkScalarAve(len0, len1);
+        if (NULL != coverage) {
+            *coverage = SkScalarAve(len0, len1);
+        }
         return true;
     }
     return false;