Image filters: implement SkImage::makeWithFilter().

gm/imagemakewithfilter.cpp

Index: gm/imagemakewithfilter.cpp
diff --git a/gm/imagemakewithfilter.cpp b/gm/imagemakewithfilter.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..1180aff7d252173740122e38ddb84c7a3fe85312
--- /dev/null
+++ b/gm/imagemakewithfilter.cpp
@@ -0,0 +1,99 @@
+/*
+ * 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 "gm.h"
+#include "SkBlurImageFilter.h"
+#include "SkCanvas.h"
+#include "SkColorFilter.h"
+#include "SkColorFilterImageFilter.h"
+#include "SkDropShadowImageFilter.h"
+#include "SkSurface.h"
+
+///////////////////////////////////////////////////////////////////////////////
+
+static void show_bounds(SkCanvas* canvas, const SkIRect& subset, const SkIRect& clip) {
+    const SkIRect rects[] { subset, clip };
+    const SkColor colors[] { SK_ColorRED, SK_ColorBLUE };
+
+    SkPaint paint;
+    paint.setStyle(SkPaint::kStroke_Style);
+
+    for (size_t i = 0; i < SK_ARRAY_COUNT(rects); ++i) {
+        paint.setColor(colors[i]);
+        canvas->drawRect(SkRect::Make(rects[i]), paint);
+    }
+}
+

[robertphillips, 2016/05/19 16:35:19]

// In this GM we're going to feed the inner portion of a 100x100 checkboard
(i.e., strip off a 25 wide border) through the makeWithFilter method. 
// We'll then draw the appropriate subset of the result to the screen at the
given off set.

[Stephen White, 2016/05/19 17:44:03]

Done.. (but isn't that what the code says? :) )

+class ImageMakeWithFilterGM : public skiagm::GM {
+public:
+    ImageMakeWithFilterGM () {}
+
+protected:
+    SkString onShortName() override {
+        return SkString("imagemakewithfilter");
+    }
+
+    SkISize onISize() override { return SkISize::Make(320, 100); }
+
+    void onDraw(SkCanvas* canvas) override {
+        auto cf = SkColorFilter::MakeModeFilter(SK_ColorGREEN, SkXfermode::kSrc_Mode);
+        sk_sp<SkImageFilter> filters[] = {
+            SkColorFilterImageFilter::Make(std::move(cf), nullptr),
+            SkBlurImageFilter::Make(2.0f, 2.0f, nullptr),
+            SkDropShadowImageFilter::Make(
+                10.0f, 5.0f, 3.0f, 3.0f, SK_ColorBLUE,
+                SkDropShadowImageFilter::kDrawShadowAndForeground_ShadowMode,
+                nullptr),
+        };
+
+        const SkIRect clipBounds[] {
+            { -20, -20, 100, 100 },
+            {   0,   0,  75,  75 },
+            {  20,  20, 100, 100 },
+            { -20, -20,  50,  50 },
+            {  20,  20,  50,  50 },
+        };
+
+        const SkImageInfo info = SkImageInfo::MakeN32(100, 100, kPremul_SkAlphaType);
+        SkScalar MARGIN = SkIntToScalar(40);

[robertphillips, 2016/05/19 16:35:19]

constify DX too ?
maybe even MARGIN ?

[Stephen White, 2016/05/19 17:44:03]

const POD local variables are a pet peeve of mine: They've always struck me as
just noise: I've never, ever seen them catch a bug, and the compiler can
optimize perfectly well without them. Is there an argument I'm missing?

(But now you've drawn my attention to them, I've removed them all. :)

+        SkScalar DX = info.width() + MARGIN;
+        const SkScalar DY = info.height() + MARGIN;
+
+        canvas->translate(MARGIN, MARGIN);
+
+        sk_sp<SkSurface> surface = canvas->makeSurface(info);
+        if (!surface) {
+            surface = SkSurface::MakeRaster(info);
+        }
+        sk_tool_utils::draw_checkerboard(surface->getCanvas());
+        sk_sp<SkImage> source = surface->makeImageSnapshot();
+
+        for (auto clipBound : clipBounds) {
+            canvas->save();
+            for (size_t i = 0; i < SK_ARRAY_COUNT(filters); ++i) {
+                SkIRect subset = SkIRect::MakeXYWH(25, 25, 50, 50);
+                SkIRect outSubset;
+                SkIPoint offset;
+                sk_sp<SkImage> result = source->makeWithFilter(filters[i].get(), subset, clipBound,
+                                                               &outSubset, &offset);
+                SkASSERT(result);
+                SkASSERT(source->isTextureBacked() == result->isTextureBacked());
+                result = result->makeSubset(outSubset);
+                canvas->drawImage(result.get(), SkIntToScalar(offset.fX), SkIntToScalar(offset.fY));
+                show_bounds(canvas, SkIRect::MakeXYWH(offset.x(), offset.y(), outSubset.width(),
+                                                      outSubset.height()), clipBound);
+                canvas->translate(DX, 0);
+            }
+            canvas->restore();
+            canvas->translate(0, DY);
+        }
+    }
+
+private:
+    typedef GM INHERITED;
+};
+DEF_GM( return new ImageMakeWithFilterGM; )