New benchmark to measure GPU mip-mapping performance

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2030673002

Review-Url: https://codereview.chromium.org/2030673002

bench/GrMipMapBench.cpp

@@ -0,0 +1,74 @@
+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "Benchmark.h"
+#include "SkCanvas.h"
+#include "SkImage.h"
+#include "SkPaint.h"
+#include "SkSurface.h"
+
+#if SK_SUPPORT_GPU
+
+class GrMipMapBench: public Benchmark {
+    sk_sp<SkSurface> fSurface;
+    SkString fName;
+    const int fW, fH;
+
+public:
+    GrMipMapBench(int w, int h) : fW(w), fH(h) {
+        fName.printf("gr_mipmap_build_%dx%d", w, h);
+    }
+
+protected:
+    bool isSuitableFor(Backend backend) override {
+        return kGPU_Backend == backend;
+    }
+
+    const char* onGetName() override { return fName.c_str(); }
+
+    void onDraw(int loops, SkCanvas* canvas) override {
+        if (!fSurface) {
+            GrContext* context = canvas->getGrContext();
+            if (nullptr == context) {
+                return;
+            }
+            SkImageInfo info = SkImageInfo::Make(fW, fH, kN32_SkColorType, kPremul_SkAlphaType,
+                                                 kSRGB_SkColorProfileType);
+            fSurface = SkSurface::MakeRenderTarget(context, SkBudgeted::kNo, info);
+        }
+
+        // Clear surface once:
+        fSurface->getCanvas()->clear(SK_ColorBLACK);
+
+        SkPaint paint;
+        paint.setFilterQuality(kMedium_SkFilterQuality);
+
+        for (int i = 0; i < loops; i++) {
+            // Touch surface so mips are dirtied
+            fSurface->getCanvas()->drawPoint(0, 0, SK_ColorWHITE);
+
+            // Draw reduced version of surface to original canvas, to trigger mip generation
+            canvas->save();
+            canvas->scale(0.1f, 0.1f);
+            canvas->drawImage(fSurface->makeImageSnapshot(SkBudgeted::kNo), 0, 0, &paint);
+            canvas->restore();
+        }
+    }
+
+private:
+    typedef Benchmark INHERITED;
+};
+
+// Build variants that exercise the width and heights being even or odd at each level, as the
+// impl specializes on each of these.
+//
+DEF_BENCH( return new GrMipMapBench(511, 1023); )
+DEF_BENCH( return new GrMipMapBench(512, 511); )
+DEF_BENCH( return new GrMipMapBench(511, 512); )
+DEF_BENCH( return new GrMipMapBench(512, 512); )
+
+#endif