Fix local matrix for crop rects in backdrop image filters

Bug: chromium:955467
Change-Id: I1c4cae2499db926aa6b629e8d730fcc8cb45be6d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/212030
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Michael Ludwig <michaelludwig@google.com>

gm/backdrop_imagefilter_croprect.cpp

@@ -0,0 +1,79 @@
+/*
+ * 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/gm.h"
+#include "include/core/SkCanvas.h"
+#include "include/effects/SkBlurImageFilter.h"
+#include "include/effects/SkColorFilterImageFilter.h"
+#include "include/core/SkPaint.h"
+
+// This draws correctly if there's a small cyan rectangle above a much larger magenta rectangle.
+// There should be no red around the cyan rectangle and no green within the magenta rectangle.
+
+DEF_SIMPLE_GM(backdrop_imagefilter_croprect, canvas, 600, 500) {
+    // CTM translates to (150, 150)
+    SkPoint origin = SkPoint::Make(150.f, 150.f);
+    // The save layer specified after the CTM has negative coordinates, but
+    // means that (100, 100) to (500, 250) in device-space will be saved
+    SkRect clip = SkRect::MakeXYWH(-50.f, -50.f, 400.f, 150.f);
+    // The image-filter crop relative to the CTM, which will map to
+    // (200, 160) to (400, 190) in device space, or (100, 600) to (300, 90) in
+    // the layer's image space.
+    SkRect cropInLocal = SkRect::MakeLTRB(50.f, 10.f, 250.f, 40.f);
+
+    SkImageFilter::CropRect cropRect(cropInLocal);
+    float matrix[20] = {-1.f, 0.f, 0.f, 0.f, 1.f,
+                        0.f, -1.f, 0.f, 0.f, 1.f,
+                        0.f, 0.f, -1.f, 0.f, 1.f,
+                        0.f, 0.f, 0.f, 1.f, 0.f};
+    sk_sp<SkColorFilter> colorFilter = SkColorFilters::Matrix(matrix);
+    sk_sp<SkImageFilter> imageFilter = SkColorFilterImageFilter::Make(colorFilter, nullptr,
+                                                                      &cropRect);
+
+    SkPaint p;
+    SkPaint l;
+    l.setStyle(SkPaint::kStroke_Style);
+    l.setStrokeWidth(0.f);
+
+    for (int i = 0; i < 2; ++i) {
+        canvas->save();
+        canvas->translate(origin.fX, origin.fY);
+
+        canvas->clipRect(clip);
+
+        if (i == 0) {
+            // Primary save layer mode, so save layer before drawing the content
+            SkPaint imfPaint;
+            imfPaint.setImageFilter(imageFilter);
+            canvas->saveLayer(nullptr, &imfPaint);
+        } // else backdrop mode, so the content is drawn first
+
+        // Fill the clip with one color (cyan for i == 0 (inverse = red), and
+        // magenta for i == 1 (inverse = green))
+        p.setColor(i == 0 ? SK_ColorCYAN : SK_ColorMAGENTA);
+        canvas->drawPaint(p);
+
+        // Then an inner rectangle with a color meant to be inverted by the image filter
+        p.setColor(i == 0 ? SK_ColorRED : SK_ColorGREEN);
+        canvas->drawRect(cropInLocal, p);
+
+        if (i == 1) {
+            // Backdrop mode, so save a layer using the image filter as the backdrop to filter
+            // content on initialization.
+            canvas->saveLayer({nullptr, nullptr, imageFilter.get(), nullptr, nullptr,
+                               SkCanvas::kInitWithPrevious_SaveLayerFlag});
+        }
+
+        // Restore the saved layer (either a main layer that was just drawn into and needs to be
+        // filtered, or an "empty" layer initialized with the previously filtered backdrop)
+        canvas->restore();
+
+        // Move down
+        canvas->restore();
+        origin.fY += 150.f;
+    }
+}

gn/gm.gni

@@ -27,6 +27,7 @@ gm_sources = [
   "$_gm/atlastext.cpp",
   "$_gm/b_119394958.cpp",
   "$_gm/backdrop.cpp",
+  "$_gm/backdrop_imagefilter_croprect.cpp",
   "$_gm/badpaint.cpp",
   "$_gm/beziereffects.cpp",
   "$_gm/beziers.cpp",

src/core/SkCanvas.cpp

@@ -938,13 +938,17 @@ void SkCanvas::DrawDeviceWithFilter(SkBaseDevice* src, const SkImageFilter* filt
     draw.fMatrix = &SkMatrix::I();
     draw.fRC = &rc;
 
-    SkPaint p;
-    if (filter) {
-        p.setImageFilter(filter->makeWithLocalMatrix(ctm));
-    }
-
     int x = src->getOrigin().x() - dstOrigin.x();
     int y = src->getOrigin().y() - dstOrigin.y();
+
+    SkPaint p;
+    if (filter) {
+        SkMatrix actm = ctm;
+        // Account for the origin offset in the local matrix
+        actm.postTranslate(x, y);
+        p.setImageFilter(filter->makeWithLocalMatrix(actm));
+    }
+
     auto special = src->snapSpecial();
     if (special) {
         dst->drawSpecial(special.get(), x, y, p, nullptr, SkMatrix::I());