Don't pass subpixel offsets through non-translation transforms

third_party/WebKit/LayoutTests/virtual/disable-spinvalidation/paint/invalidation/subpixel-offset-scaled-transform-expected.txt

Index: third_party/WebKit/LayoutTests/virtual/disable-spinvalidation/paint/invalidation/subpixel-offset-scaled-transform-expected.txt
diff --git a/third_party/WebKit/LayoutTests/virtual/disable-spinvalidation/paint/invalidation/subpixel-offset-scaled-transform-expected.txt b/third_party/WebKit/LayoutTests/virtual/disable-spinvalidation/paint/invalidation/subpixel-offset-scaled-transform-expected.txt
new file mode 100644
index 0000000000000000000000000000000000000000..fe2b675ef3738dd2daf4651db892c89e65c06e5b
--- /dev/null
+++ b/third_party/WebKit/LayoutTests/virtual/disable-spinvalidation/paint/invalidation/subpixel-offset-scaled-transform-expected.txt
@@ -0,0 +1,280 @@
+{
+  "layers": [
+    {
+      "name": "LayoutView #document",
+      "bounds": [800, 600],
+      "contentsOpaque": true,
+      "drawsContent": true,
+      "paintInvalidations": [
+        {
+          "object": "LayoutBlockFlow (relative positioned) DIV class='child scale'",
+          "rect": [8, 58, 42, 40],
+          "reason": "bounds change"
+        },
+        {
+          "object": "LayoutBlockFlow (relative positioned) DIV class='child'",
+          "rect": [23, 8, 41, 40],

[Xianzhu, 2017/04/27 22:53:55]

*This is disable-spinvalidation*.

The invalidation rect is incorrect or inconsistent with where we paint the
child. The child is painted at (8,8 40x40) and (8.3,8 40x40) before and after
repaintTest, respectively. The local offset (0.4, 0) is rounded off when
snapping to "pixels" in the child's space during painting.

The invalidation rect is from the slow path (MapToVisualRectInAncestorSpace())
in PaintInvalidationState.

                   PaintInvalidator  MapToVisualRectInAncestorSpace
LocalVisualRect    (0,0 1x1)         (0,0 1x1)
+local offset      (0.4,0 1x1)       (0.4,0 1x1)
EnclosingIntRect   (0,0 2x1)
Transformed        (0,0 80x40)       (~15,0 40x40)
EnclosingBoundingBox                 (~15,0 41x40)
+container offset  (8.3,8 80x40)     (~23,8 41x40)

The difference comes from the EnclosingIntRect step. Should we call
EnclosingIntRect() before applying transform in MapToVisualRectInAncestorSpace?
It was changed to EnclosingBoundingRect after transform in
https://codereview.chromium.org/2727093002.

[chrishtr, 2017/04/28 02:23:53]

I think in general it has to be that way, at least for non-spinvalidation,
because the paint
offset is not known, so invalidations for 2D transforms that are "identity or
translation" would
incur under-invalidations.

+          "reason": "location change"
+        },
+        {
+          "object": "LayoutBlockFlow (relative positioned) DIV class='child scale'",
+          "rect": [8, 58, 41, 40],
+          "reason": "bounds change"
+        }
+      ],
+      "underPaintInvalidations": [
+        {
+          "x": 8,
+          "y": 8,
+          "oldPixel": "#0000FF",
+          "newPixel": "#4B4BFF"
+        },
+        {
+          "x": 8,
+          "y": 9,
+          "oldPixel": "#0000FF",
+          "newPixel": "#4B4BFF"
+        },
+        {
+          "x": 8,
+          "y": 10,
+          "oldPixel": "#0000FF",
+          "newPixel": "#4B4BFF"
+        },
+        {
+          "x": 8,
+          "y": 11,
+          "oldPixel": "#0000FF",
+          "newPixel": "#4B4BFF"
+        },
+        {
+          "x": 8,
+          "y": 12,
+          "oldPixel": "#0000FF",
+          "newPixel": "#4B4BFF"
+        },
+        {
+          "x": 8,
+          "y": 13,
+          "oldPixel": "#0000FF",
+          "newPixel": "#4B4BFF"
+        },
+        {
+          "x": 8,
+          "y": 14,
+          "oldPixel": "#0000FF",
+          "newPixel": "#4B4BFF"
+        },
+        {
+          "x": 8,
+          "y": 15,
+          "oldPixel": "#0000FF",
+          "newPixel": "#4B4BFF"
+        },
+        {
+          "x": 8,
+          "y": 16,
+          "oldPixel": "#0000FF",
+          "newPixel": "#4B4BFF"
+        },
+        {
+          "x": 8,
+          "y": 17,
+          "oldPixel": "#0000FF",
+          "newPixel": "#4B4BFF"
+        },
+        {
+          "x": 8,
+          "y": 18,
+          "oldPixel": "#0000FF",
+          "newPixel": "#4B4BFF"
+        },
+        {
+          "x": 8,
+          "y": 19,
+          "oldPixel": "#0000FF",
+          "newPixel": "#4B4BFF"
+        },
+        {
+          "x": 8,
+          "y": 20,
+          "oldPixel": "#0000FF",
+          "newPixel": "#4B4BFF"
+        },
+        {
+          "x": 8,
+          "y": 21,
+          "oldPixel": "#0000FF",
+          "newPixel": "#4B4BFF"
+        },
+        {
+          "x": 8,
+          "y": 22,
+          "oldPixel": "#0000FF",
+          "newPixel": "#4B4BFF"
+        },
+        {
+          "x": 8,
+          "y": 23,
+          "oldPixel": "#0000FF",
+          "newPixel": "#4B4BFF"
+        },
+        {
+          "x": 8,
+          "y": 24,
+          "oldPixel": "#0000FF",
+          "newPixel": "#4B4BFF"
+        },
+        {
+          "x": 8,
+          "y": 25,
+          "oldPixel": "#0000FF",
+          "newPixel": "#4B4BFF"
+        },
+        {
+          "x": 8,
+          "y": 26,
+          "oldPixel": "#0000FF",
+          "newPixel": "#4B4BFF"
+        },
+        {
+          "x": 8,
+          "y": 27,
+          "oldPixel": "#0000FF",
+          "newPixel": "#4B4BFF"
+        },
+        {
+          "x": 8,
+          "y": 28,
+          "oldPixel": "#0000FF",
+          "newPixel": "#4B4BFF"
+        },
+        {
+          "x": 8,
+          "y": 29,
+          "oldPixel": "#0000FF",
+          "newPixel": "#4B4BFF"
+        },
+        {
+          "x": 8,
+          "y": 30,
+          "oldPixel": "#0000FF",
+          "newPixel": "#4B4BFF"
+        },
+        {
+          "x": 8,
+          "y": 31,
+          "oldPixel": "#0000FF",
+          "newPixel": "#4B4BFF"
+        },
+        {
+          "x": 8,
+          "y": 32,
+          "oldPixel": "#0000FF",
+          "newPixel": "#4B4BFF"
+        },
+        {
+          "x": 8,
+          "y": 33,
+          "oldPixel": "#0000FF",
+          "newPixel": "#4B4BFF"
+        },
+        {
+          "x": 8,
+          "y": 34,
+          "oldPixel": "#0000FF",
+          "newPixel": "#4B4BFF"
+        },
+        {
+          "x": 8,
+          "y": 35,
+          "oldPixel": "#0000FF",
+          "newPixel": "#4B4BFF"
+        },
+        {
+          "x": 8,
+          "y": 36,
+          "oldPixel": "#0000FF",
+          "newPixel": "#4B4BFF"
+        },
+        {
+          "x": 8,
+          "y": 37,
+          "oldPixel": "#0000FF",
+          "newPixel": "#4B4BFF"
+        },
+        {
+          "x": 8,
+          "y": 38,
+          "oldPixel": "#0000FF",
+          "newPixel": "#4B4BFF"
+        },
+        {
+          "x": 8,
+          "y": 39,
+          "oldPixel": "#0000FF",
+          "newPixel": "#4B4BFF"
+        },
+        {
+          "x": 8,
+          "y": 40,
+          "oldPixel": "#0000FF",
+          "newPixel": "#4B4BFF"
+        },
+        {
+          "x": 8,
+          "y": 41,
+          "oldPixel": "#0000FF",
+          "newPixel": "#4B4BFF"
+        },
+        {
+          "x": 8,
+          "y": 42,
+          "oldPixel": "#0000FF",
+          "newPixel": "#4B4BFF"
+        },
+        {
+          "x": 8,
+          "y": 43,
+          "oldPixel": "#0000FF",
+          "newPixel": "#4B4BFF"
+        },
+        {
+          "x": 8,
+          "y": 44,
+          "oldPixel": "#0000FF",
+          "newPixel": "#4B4BFF"
+        },
+        {
+          "x": 8,
+          "y": 45,
+          "oldPixel": "#0000FF",
+          "newPixel": "#4B4BFF"
+        },
+        {
+          "x": 8,
+          "y": 46,
+          "oldPixel": "#0000FF",
+          "newPixel": "#4B4BFF"
+        },
+        {
+          "x": 8,
+          "y": 47,
+          "oldPixel": "#0000FF",
+          "newPixel": "#4B4BFF"
+        }
+      ]
+    }
+  ],
+  "objectPaintInvalidations": [
+    {
+      "object": "LayoutBlockFlow (relative positioned) DIV class='child'",
+      "reason": "location change"
+    },
+    {
+      "object": "LayoutBlockFlow (relative positioned) DIV class='child scale'",
+      "reason": "bounds change"
+    }
+  ]
+}
+