Bugfix for Nexus 5 mipmap+scissor generation failure

Bug: skia:8664
Change-Id: Ic1b4f5afb2847eabb2290cbba808c5692a876972
Reviewed-on: https://skia-review.googlesource.com/c/182152
Auto-Submit: Michael Ludwig <michaelludwig@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>

gm/skbug_8664.cpp

@@ -0,0 +1,58 @@
+/*
+ * Copyright 2019 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "gm.h"
+
+#include "Resources.h"
+
+DEF_SIMPLE_GM(skbug_8664, canvas, 830, 550) {
+    const struct {
+        SkScalar    fSx, fSy, fTx, fTy;
+    } xforms[] = {
+        { 1, 1, 0, 0 },
+        { 0.5f, 0.5f, 530, 0 },
+        { 0.25f, 0.25f, 530, 275 },
+        { 0.125f, 0.125f, 530, 420 },
+    };
+
+    SkPaint imagePaint;
+    // Must be at least medium to require mipmaps when we downscale the image
+    imagePaint.setFilterQuality(kMedium_SkFilterQuality);
+    sk_sp<SkImage> image(GetResourceAsImage("images/mandrill_512.png"));
+
+    SkPaint overlayPaint;
+    overlayPaint.setColor(0x80FFFFFF);
+
+    // Make the overlay visible even when the downscaled images fail to render
+    canvas->clear(0xFF888888);
+
+    canvas->translate(20, 20);
+    for (const auto& xform : xforms) {
+        canvas->save();
+        canvas->translate(xform.fTx, xform.fTy);
+        canvas->scale(xform.fSx, xform.fSy);
+
+        // Draw an image, possibly down sampled, which forces us to generate mipmaps inline
+        // on the second iteration.
+        canvas->drawImage(image, 0, 0, &imagePaint);
+
+        // Draw an overlay that requires the scissor test for its clipping, so that the mipmap
+        // generation + scissor interference bug is highlighted in Adreno 330 devices.
+        SkRect inner = SkRect::MakeLTRB(32.f, 32.f, 480.f, 480.f);
+        SkRect outer = inner.makeOutset(16.f, 16.f);
+
+        // Clip to smaller rectangle
+        canvas->save();
+        canvas->clipRect(inner);
+        // Then apply a rotation and draw a larger rectangle to ensure the clip cannot be dropped
+        canvas->rotate(20.f);
+        canvas->drawRect(outer, overlayPaint);
+        canvas->restore();
+
+        canvas->restore();
+    }
+}

gn/gm.gni

@@ -299,6 +299,7 @@ gm_sources = [
   "$_gm/skbug_257.cpp",
   "$_gm/skbug_4868.cpp",
   "$_gm/skbug_5321.cpp",
+  "$_gm/skbug_8664.cpp",
   "$_gm/skbug1719.cpp",
   "$_gm/skinning.cpp",
   "$_gm/smallarc.cpp",