Initial scene graph (SkSG)

Sketching a thin (as in close-to-skia-semantics) scene graph API, focused on
external animation, inval tracking and minimal repaint.

Only a few concrete classes/features so far:

* Rect/Color/Transform/Group
* basic inval tracking
* a trivial animated sample with inval visualization

Pretty much everything (especially naming) is volatile, so treat accordingly.

The interesting bits to review are likely in Node.{h,cpp} for inval and
SampleSGInval.cpp for usage.

Initial class hierarchy:

  * Node: invalidation/ancestors tracking
  |
   -- * RenderNode: onRender(SkCanvas)
  |   |
  |    -- * Draw (concrete): rendering a [geometry, paint] tuple
  |   |
  |    -- * Group (concrete): grouping multiple RenderNodes
  |   |
  |    -- * EffectNode: single-descendant effect wrapper
  |       |
  |        -- * Transform (concrete): transform effect
  |
   -- * PaintNode: onMakePaint()
  |   |
  |    -- * Color (concrete): SkColor paint wrapper
  |
   -- * GeometryNode: onComputeBounds(), onDraw(SkCanvas, SkPaint)
      |
       -- * Rect (concrete): SkRect wrapper

TBR=

Change-Id: Iacf9b773c181a7582ecd31ee968562f179d1aa1b
Reviewed-on: https://skia-review.googlesource.com/85502
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Florin Malita <fmalita@chromium.org>
diff --git a/BUILD.gn b/BUILD.gn
index 3f1ce7f..69bcb68 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -1278,6 +1278,7 @@
     public_include_dirs = [ "gm" ]
     sources = gm_sources
     deps = [
+      ":experimental_sksg",
       ":flags",
       ":gpu_tool_utils",
       ":skia",
@@ -1293,6 +1294,7 @@
       sources -= [ "//tests/FontMgrAndroidParserTest.cpp" ]
     }
     deps = [
+      ":experimental_sksg",
       ":experimental_svg_model",
       ":flags",
       ":skia",
@@ -1350,6 +1352,31 @@
     ]
   }
 
+  test_lib("experimental_sksg") {
+    public_include_dirs = [
+      "experimental/sksg",
+      "experimental/sksg/effects",
+      "experimental/sksg/geometry",
+      "experimental/sksg/paint",
+    ]
+    sources = [
+      "experimental/sksg/SkSGDraw.cpp",
+      "experimental/sksg/SkSGEffectNode.cpp",
+      "experimental/sksg/SkSGGeometryNode.cpp",
+      "experimental/sksg/SkSGGroup.cpp",
+      "experimental/sksg/SkSGInvalidationController.cpp",
+      "experimental/sksg/SkSGNode.cpp",
+      "experimental/sksg/SkSGPaintNode.cpp",
+      "experimental/sksg/SkSGRenderNode.cpp",
+      "experimental/sksg/effects/SkSGTransform.cpp",
+      "experimental/sksg/geometry/SkSGRect.cpp",
+      "experimental/sksg/paint/SkSGColor.cpp",
+    ]
+    deps = [
+      ":skia",
+    ]
+  }
+
   if (target_cpu != "wasm") {
     test_lib("views") {
       public_include_dirs = [ "include/views" ]
@@ -1432,6 +1459,7 @@
                   "src/core/SkThreadedBMPDevice.h",
                 ]
       deps = [
+        ":experimental_sksg",
         ":experimental_svg_model",
         ":flags",
         ":gm",
@@ -1459,6 +1487,7 @@
       include_dirs = [ "tests" ]
       deps = [
         ":common_flags",
+        ":experimental_sksg",
         ":experimental_svg_model",
         ":flags",
         ":gm",
@@ -1497,6 +1526,7 @@
     deps = [
       ":bench",
       ":common_flags",
+      ":experimental_sksg",
       ":experimental_svg_model",
       ":flags",
       ":gm",