[SVGDom/experimental] Initial SVGLength support

experimental/svg/model/SkSVGRenderContext.h

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkSVGRenderContext_DEFINED
 #define SkSVGRenderContext_DEFINED
 
+#include "SkSize.h"
 #include "SkPaint.h"
 #include "SkTLazy.h"
 
 class SkPaint;
+class SkSVGLength;
+
+class SkSVGLengthContext {
+public:

[robertphillips, 2016/08/02 22:25:56]

Can viewports ever be not based at the origin?

[f(malita), 2016/08/03 16:50:51]

Logically, yes, but I don't think the location matters for length resolution
purposes: viewports also establish new coordinate systems with the origin ==
viewport location.  Dependent lengths are resolved within this local coordinate
system, so for them the viewport location is always (0,0).

https://www.w3.org/TR/SVG/coords.html#EstablishingANewViewport

+    SkSVGLengthContext(const SkSize& viewport) : fViewport(viewport) {}
+
+    enum class LengthType {

[robertphillips, 2016/08/02 22:25:56]

k prefixes ?

[f(malita), 2016/08/03 16:50:51]

Done.

+        Horizontal,
+        Vertical,
+        Other,
+    };
+
+    void setViewPort(const SkSize& viewport) { fViewport = viewport; }
+
+    SkScalar resolve(const SkSVGLength&, LengthType) const;
+
+private:
+    SkSize fViewport;
+};
 
 class SkSVGRenderContext {
 public:
-    SkSVGRenderContext();
+    explicit SkSVGRenderContext(const SkSize& initialViewport);
     SkSVGRenderContext(const SkSVGRenderContext&) = default;
     SkSVGRenderContext& operator=(const SkSVGRenderContext&);
 
+    const SkSVGLengthContext& lengthContext() const { return fLengthContext; }
+
     const SkPaint* fillPaint() const { return fFill.getMaybeNull(); }
     const SkPaint* strokePaint() const { return fStroke.getMaybeNull(); }
 
     void setFillColor(SkColor);
     void setStrokeColor(SkColor);
 
 private:
     SkPaint& ensureFill();
     SkPaint& ensureStroke();
 
-    SkTLazy<SkPaint> fFill;
-    SkTLazy<SkPaint> fStroke;
+    SkSVGLengthContext fLengthContext;
+    SkTLazy<SkPaint>   fFill;
+    SkTLazy<SkPaint>   fStroke;
 };
 
 #endif // SkSVGRenderContext_DEFINED