Add GM to exercise some of the darker corners of SkMagnifierImageFilter

An upcoming CL (https://skia-review.googlesource.com/c/7995/ (Remove asTextureRef from SkSpecialImage & update effects accordingly)) modifies some untested portions of the SkMagnifierImageFilter.

This adds a test to prevents regressions.

Change-Id: I9fa406f699e39fa393212e7f63a457b015b36edb
Reviewed-on: https://skia-review.googlesource.com/8023
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>

gm/simple_magnification.cpp

@@ -0,0 +1,112 @@
+/*
+ * Copyright 2017 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 "SkImageSource.h"
+#include "SkMagnifierImageFilter.h"
+#include "SkSurface.h"
+
+static sk_sp<SkImage> make_image(GrContext* context, int size, GrSurfaceOrigin origin) {
+    if (context) {
+        SkImageInfo ii = SkImageInfo::Make(size, size, kN32_SkColorType, kPremul_SkAlphaType);
+        sk_sp<SkSurface> surf(SkSurface::MakeRenderTarget(context, SkBudgeted::kYes, ii, 0,
+                                                          origin, nullptr));
+
+        SkCanvas* canvas = surf->getCanvas();
+
+        canvas->clear(SK_ColorRED);
+        canvas->drawPoint(1.5f, 1.5f, SK_ColorGREEN);
+        canvas->drawPoint(2.5f, 1.5f, SK_ColorBLUE);
+        canvas->drawPoint(1.5f, 2.5f, SK_ColorCYAN);
+        canvas->drawPoint(2.5f, 2.5f, SK_ColorGRAY);
+
+        return surf->makeImageSnapshot();
+    } else {
+        SkBitmap bm;
+        bm.allocN32Pixels(size, size);
+        bm.eraseRGB(255, 0, 0);
+        *bm.getAddr32(1, 1) = SkPackARGB32(0xFF, 0x00, 0xFF, 0x00);
+        *bm.getAddr32(2, 1) = SkPackARGB32(0xFF, 0x00, 0x00, 0xFF);
+        *bm.getAddr32(1, 2) = SkPackARGB32(0xFF, 0x00, 0xFF, 0xFF);
+        *bm.getAddr32(2, 2) = SkPackARGB32(0xFF, 0x88, 0x88, 0x88);
+
+        return SkImage::MakeFromBitmap(bm);
+    }
+}
+
+/*
+ * This GM creates an image with a 2x2:
+ *    Green | Blue
+ *    ------------
+ *    Cyan  | Gray
+ * block of pixels in one corner of a 33x33 field. The 'srcRect' feature of the
+ * SkMagnifierImageFilter is then used to blow it up with different inset border widths.
+ *
+ * In GPU-mode we wind up drawing 4 rects:
+ *
+ *     BottomLeft origin + 1-wide inset | TopLeft origin + 1-wide inset
+ *     ----------------------------------------------------------------
+ *     BottomLeft origin + 7-wide inset | TopLeft origin + 7-wide inset
+ *
+ * In Raster-mode the source origin isn't used.
+ */
+class SimpleMagnificationGM : public skiagm::GM {
+public:
+    SimpleMagnificationGM() {
+        this->setBGColor(sk_tool_utils::color_to_565(0xFFCCCCCC));
+    }
+
+protected:
+    SkString onShortName() override {
+        return SkString("simple-magnification");
+    }
+
+    SkISize onISize() override {
+        return SkISize::Make(3*kPad+2*kImgSize, 3*kPad+2*kImgSize);
+    }
+
+    void draw(SkCanvas* canvas, sk_sp<SkImage> image, const SkIPoint& offset, int inset) {
+        sk_sp<SkImageFilter> imgSrc(SkImageSource::Make(std::move(image)));
+
+        SkRect srcRect = SkRect::MakeXYWH(1.0f, 1.0f, 2.0f, 2.0f);
+        sk_sp<SkImageFilter> magFilter(SkMagnifierImageFilter::Make(srcRect, inset, imgSrc));
+
+        SkPaint paint;
+        paint.setImageFilter(std::move(magFilter));
+
+        canvas->save();
+        canvas->translate(offset.fX, offset.fY);
+        SkRect rect = SkRect::MakeWH(kImgSize, kImgSize);
+        canvas->drawRect(rect, paint);
+
+        canvas->restore();
+    }
+
+    void onDraw(SkCanvas* canvas) override {
+        GrContext* context = canvas->getGrContext();
+
+        sk_sp<SkImage> bottomLImg = make_image(context, kImgSize, kBottomLeft_GrSurfaceOrigin);
+        sk_sp<SkImage> topLImg = make_image(context, kImgSize, kTopLeft_GrSurfaceOrigin);
+
+        int bigOffset = 2 * kPad + kImgSize;
+
+        this->draw(canvas, bottomLImg, SkIPoint::Make(kPad, kPad), 1);
+        this->draw(canvas, topLImg, SkIPoint::Make(bigOffset, kPad), 1);
+        this->draw(canvas, bottomLImg, SkIPoint::Make(kPad, bigOffset), 7);
+        this->draw(canvas, topLImg, SkIPoint::Make(bigOffset, bigOffset), 7);
+    }
+
+private:
+    static const int kImgSize = 33;
+    static const int kPad = 2;
+
+    typedef skiagm::GM INHERITED;
+};
+
+//////////////////////////////////////////////////////////////////////////////
+
+DEF_GM(return new SimpleMagnificationGM;)

gn/gm.gni

@@ -253,6 +253,7 @@ gm_sources = [
   "$_gm/shapes.cpp",
   "$_gm/showmiplevels.cpp",
   "$_gm/simpleaaclip.cpp",
+  "$_gm/simple_magnification.cpp",
   "$_gm/simplerect.cpp",
   "$_gm/skbug_257.cpp",
   "$_gm/skbug_4868.cpp",

src/effects/SkImageSource.cpp

@@ -83,13 +83,21 @@ sk_sp<SkSpecialImage> SkImageSource::onFilterImage(SkSpecialImage* source, const
     ctx.ctm().mapRect(&dstRect, fDstRect);
 
     SkRect bounds = SkRect::MakeIWH(fImage->width(), fImage->height());
-    if (fSrcRect == bounds && dstRect == bounds) {
-        // No regions cropped out or resized; return entire image.
-        offset->fX = offset->fY = 0;
+    if (fSrcRect == bounds) {
+        int iLeft = dstRect.fLeft;
+        int iTop = dstRect.fTop;
+        // TODO: this seems to be a very noise-prone way to determine this (esp. the floating-point
+        // widths & heights).
+        if (dstRect.width() == bounds.width() && dstRect.height() == bounds.height() &&
+            iLeft == dstRect.fLeft && iTop == dstRect.fTop) {
+            // The dest is just an un-scaled integer translation of the entire image; return it
+            offset->fX = iLeft;
+            offset->fY = iTop;
             return SkSpecialImage::MakeFromImage(SkIRect::MakeWH(fImage->width(), fImage->height()),
                                                  fImage, ctx.outputProperties().colorSpace(),
                                                  &source->props());
         }
+    }
 
     const SkIRect dstIRect = dstRect.roundOut();