Remove CTM-dependent paintBoxShadow() heuristic

Source/core/paint/BoxPainter.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "config.h"
 #include "core/paint/BoxPainter.h"
 
 #include "core/HTMLNames.h"
 #include "core/frame/Settings.h"
 #include "core/html/HTMLFrameOwnerElement.h"
@@ skipping 1991 matching lines @@
 
             // Save the state and clip, if not already done.
             // The clip does not depend on any shadow-specific properties.
             if (!stateSaver.saved()) {
                 stateSaver.save();
                 if (hasBorderRadius) {
                     FloatRoundedRect rectToClipOut = border;
 
                     // If the box is opaque, it is unnecessary to clip it out. However, doing so saves time
                     // when painting the shadow. On the other hand, it introduces subpixel gaps along the
-                    // corners. Those are avoided by insetting the clipping path by one pixel.
+                    // corners. Those are avoided by insetting the clipping path by one CSS pixel.
                     if (hasOpaqueBackground)
                         rectToClipOut.inflateWithRadii(-1);
 
-                    if (!rectToClipOut.isEmpty()) {
+                    if (!rectToClipOut.isEmpty())
                         context->clipOutRoundedRect(rectToClipOut);
-                    }
                 } else {
                     // This IntRect is correct even with fractional shadows, because it is used for the rectangle
                     // of the box itself, which is always pixel-aligned.
                     FloatRect rectToClipOut = border.rect();
 
                     // If the box is opaque, it is unnecessary to clip it out. However, doing so saves time
                     // when painting the shadow. On the other hand, it introduces subpixel gaps along the
                     // edges if they are not pixel-aligned. Those are avoided by insetting the clipping path
-                    // by one pixel.
-                    // When Slimming Paint is enabled, turn off this heuristic. See crbug.com/382491 for details.
-                    if (hasOpaqueBackground && !RuntimeEnabledFeatures::slimmingPaintEnabled()) {
-                        // FIXME: The function to decide on the policy based on the transform should be a named function.
-                        // FIXME: It's not clear if this check is right. What about integral scale factors?
-                        // FIXME: See crbug.com/382491. The use of getCTM may also be wrong because it does not include
-                        // device zoom applied at raster time.
-                        AffineTransform transform = context->getCTM();
-                        if (transform.a() != 1 || (transform.d() != 1 && transform.d() != -1) || transform.b() || transform.c())
-                            rectToClipOut.inflate(-1);
-                    }
+                    // by one CSS pixel.
+                    if (hasOpaqueBackground)
+                        rectToClipOut.inflate(-1);
 
-                    if (!rectToClipOut.isEmpty()) {
+                    if (!rectToClipOut.isEmpty())
                         context->clipOut(rectToClipOut);
-                    }
                 }
             }
 
             // Draw only the shadow.
             context->setShadow(shadowOffset, shadowBlur, shadowColor, DrawLooperBuilder::ShadowRespectsTransforms, DrawLooperBuilder::ShadowIgnoresAlpha, DrawShadowOnly);
 
             if (hasBorderRadius) {
                 FloatRoundedRect influenceRect(pixelSnappedIntRect(LayoutRect(shadowRect)), border.radii());
                 float changeAmount = 2 * shadowBlur + shadowSpread;
                 if (changeAmount >= 0)
@@ skipping 221 matching lines @@
 
     FloatPoint secondQuad[4];
     secondQuad[0] = quad[0];
     secondQuad[1] = FloatPoint(quad[0].x() - r1 * cx, quad[0].y() - r1 * cy);
     secondQuad[2] = quad[2];
     secondQuad[3] = quad[3];
     graphicsContext->clipPolygon(4, secondQuad, !secondEdgeMatches);
 }
 
 } // namespace blink