Make a GM for checking blur bounds.

Change-Id: I30e7ac2ad37f666e3fafe94a3f52a764e1e2e652
Reviewed-on: https://skia-review.googlesource.com/88040
Commit-Queue: Herb Derby <herb@google.com>
Reviewed-by: Stephen White <senorblanco@chromium.org>
Reviewed-by: Robert Phillips <robertphillips@google.com>

1 files changed, 36 insertions, 0 deletions

diff --git a/gm/blurpositioning.cpp b/gm/blurpositioning.cpp
new file mode 100644
index 0000000000..23bacdcceb
--- /dev/null
+++ b/gm/blurpositioning.cpp
@@ -0,0 +1,36 @@
+/*
+ * 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 "SkBlurImageFilter.h"
+
+// For all sigma, the black box should be centered in the red outline. For small sigma,
+// the rectangle is not blurred, but still must be centered properly.
+
+DEF_SIMPLE_GM(check_small_sigma_offset, canvas, 200, 1200) {
+
+    for (auto sigma : {0.0, 0.1, 0.2, 0.3, 0.4, 0.6, 0.8, 1.0, 1.2}) {
+        // border calculation from SkBlurImageFilter
+        int border = SkScalarCeilToInt(sigma * 3);
+
+        SkRect r = SkRect::MakeXYWH(50, 50, 100, 50);
+        SkRect b = r.makeOutset(border + 1, border + 1);
+        b.inset(0.5f, 0.5f);
+        SkPaint p;
+        p.setColor(SK_ColorRED);
+        p.setStyle(SkPaint::Style::kStroke_Style);
+
+        canvas->drawRect(b, p);
+
+        p.reset();
+        p.setColor(SK_ColorBLACK);
+        p.setImageFilter(SkBlurImageFilter::Make(sigma, sigma, nullptr));
+        canvas->drawRect(r, p);
+
+        canvas->translate(0, 100);
+    }
+}