allow subpixel positioning w/ bitmap filtering

tests/DrawBitmapRectTest.cpp

Index: tests/DrawBitmapRectTest.cpp
diff --git a/tests/DrawBitmapRectTest.cpp b/tests/DrawBitmapRectTest.cpp
index 6dca98b527207a086178b07199d6cd839e8c6dc8..23878d30201e83f010f5d57120d5035ca1e3ed70 100644
--- a/tests/DrawBitmapRectTest.cpp
+++ b/tests/DrawBitmapRectTest.cpp
@@ -94,6 +94,7 @@ static bool treat_as_sprite(const SkMatrix& mat, const SkISize& size,
 
 static void test_treatAsSprite(skiatest::Reporter* reporter) {
     const unsigned bilerBits = kSkSubPixelBitsForBilerp;
+    const unsigned nearestNeighborBits = 0;
 
     SkMatrix mat;
     SkISize  size;
@@ -135,19 +136,19 @@ static void test_treatAsSprite(skiatest::Reporter* reporter) {
     const SkScalar twoThirds = SK_Scalar1 * 2 / 3;
     const SkScalar bigScale = SkScalarDiv(size.width() + twoThirds, size.width());
     mat.setScale(bigScale, bigScale);
-    REPORTER_ASSERT(reporter, !treat_as_sprite(mat, size, false));
+    REPORTER_ASSERT(reporter, !treat_as_sprite(mat, size, nearestNeighborBits));
     REPORTER_ASSERT(reporter, !treat_as_sprite(mat, size, bilerBits));
 
     const SkScalar oneThird = SK_Scalar1 / 3;
     const SkScalar smallScale = SkScalarDiv(size.width() + oneThird, size.width());
     mat.setScale(smallScale, smallScale);
-    REPORTER_ASSERT(reporter, treat_as_sprite(mat, size, false));
+    REPORTER_ASSERT(reporter, treat_as_sprite(mat, size, nearestNeighborBits));
     REPORTER_ASSERT(reporter, !treat_as_sprite(mat, size, bilerBits));
 
     const SkScalar oneFortyth = SK_Scalar1 / 40;
     const SkScalar tinyScale = SkScalarDiv(size.width() + oneFortyth, size.width());
     mat.setScale(tinyScale, tinyScale);
-    REPORTER_ASSERT(reporter, treat_as_sprite(mat, size, false));
+    REPORTER_ASSERT(reporter, treat_as_sprite(mat, size, nearestNeighborBits));
     REPORTER_ASSERT(reporter, treat_as_sprite(mat, size, bilerBits));
 }
 
@@ -287,6 +288,44 @@ static bool check_for_all_zeros(const SkBitmap& bm) {
     return true;
 }
 
+static void test_on_grid(skiatest::Reporter* reporter, int w, int h, const SkRect& r,
+                         SkScalar delta, int bits, bool expected) {
+    REPORTER_ASSERT(reporter, SkRectIsOnGrid(w, h, r.makeInset(delta, 0), bits) == expected);
+    REPORTER_ASSERT(reporter, SkRectIsOnGrid(w, h, r.makeInset(-delta, 0), bits) == expected);
+    REPORTER_ASSERT(reporter, SkRectIsOnGrid(w, h, r.makeInset(0, delta), bits) == expected);
+    REPORTER_ASSERT(reporter, SkRectIsOnGrid(w, h, r.makeInset(0, -delta), bits) == expected);
+
+    if (0 == bits) {
+        expected = true;
+    }
+    REPORTER_ASSERT(reporter, SkRectIsOnGrid(w, h, r.makeOffset(delta, 0), bits) == expected);
+    REPORTER_ASSERT(reporter, SkRectIsOnGrid(w, h, r.makeOffset(-delta, 0), bits) == expected);
+    REPORTER_ASSERT(reporter, SkRectIsOnGrid(w, h, r.makeOffset(0, delta), bits) == expected);
+    REPORTER_ASSERT(reporter, SkRectIsOnGrid(w, h, r.makeOffset(0, -delta), bits) == expected);
+
+}
+
+static void test_on_grid(skiatest::Reporter* reporter, int bits, SkScalar cutOff) {
+    const int width = 100;
+    const int height = 100;
+    const SkScalar eps = 0.00001f;
+
+    SkRect r;
+    r.setWH(SkIntToScalar(width), SkIntToScalar(height));
+    REPORTER_ASSERT(reporter, SkRectIsOnGrid(width, height, r, bits));
+
+    test_on_grid(reporter, width, height, r, cutOff - eps, bits, true);
+    test_on_grid(reporter, width, height, r, cutOff + eps, bits, false);
+}
+
+static void test_on_grid(skiatest::Reporter* reporter) {
+    for (int bits = 0; bits <= 8; ++bits) {
+        // The cutoff for being on the grid is  0.5 * (1/grid_size)
+        const SkScalar cutOff = SkScalarInvert(1 << (bits + 1));
+        test_on_grid(reporter, bits, cutOff);
+    }
+}
+
 static const int gWidth = 256;
 static const int gHeight = 256;
 
@@ -296,6 +335,8 @@ static void create(SkBitmap* bm, SkColor color) {
 }
 
 DEF_TEST(DrawBitmapRect, reporter) {
+    test_on_grid(reporter);
+
     SkBitmap src, dst;
 
     create(&src, 0xFFFFFFFF);