[svg] Add current node to render context

A couple of render-time decisions require knowledge of object bounding
boxes, such as gradients (whose default coordinate space is
"objectBoundingBox". This CL adds the current node being rendered to the
render context so that it can be accessed down-stack (for example, when
gradients are being resolved and added to the paint as Skia shaders).

Each node will overload the bounds computation, for now it just returns
empty bounds for all nodes. TBD if we want to cache bounds somewhere,
either inside the node object or in a separate cache.

Bug: skia:10842
Change-Id: I40061ffedcb840e4dd28dba6351421f5b4fc904b
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/329221
Commit-Queue: Tyler Denniston <tdenniston@google.com>
Reviewed-by: Florin Malita <fmalita@chromium.org>

modules/svg/include/SkSVGNode.h

@@ -15,6 +15,7 @@ class SkCanvas;
 class SkMatrix;
 class SkPaint;
 class SkPath;
+class SkSVGLengthContext;
 class SkSVGRenderContext;
 class SkSVGValue;
 
@@ -72,6 +73,7 @@ class SkSVGNode : public SkRefCnt {
     void render(const SkSVGRenderContext&) const;
     bool asPaint(const SkSVGRenderContext&, SkPaint*) const;
     SkPath asPath(const SkSVGRenderContext&) const;
+    SkRect objectBoundingBox(const SkSVGLengthContext&) const;
 
     void setAttribute(SkSVGAttribute, const SkSVGValue&);
     bool setAttribute(const char* attributeName, const char* attributeValue);
@@ -119,6 +121,10 @@ class SkSVGNode : public SkRefCnt {
 
     virtual bool hasChildren() const { return false; }
 
+    virtual SkRect onObjectBoundingBox(const SkSVGLengthContext&) const {
+        return SkRect::MakeEmpty();
+    }
+
 private:
     SkSVGTag                    fTag;
 

modules/svg/include/SkSVGRenderContext.h

@@ -59,9 +59,10 @@ struct SkSVGPresentationContext {
 class SkSVGRenderContext {
 public:
     SkSVGRenderContext(SkCanvas*, const SkSVGIDMapper&, const SkSVGLengthContext&,
-                       const SkSVGPresentationContext&);
+                       const SkSVGPresentationContext&, const SkSVGNode*);
     SkSVGRenderContext(const SkSVGRenderContext&);
     SkSVGRenderContext(const SkSVGRenderContext&, SkCanvas*);
+    SkSVGRenderContext(const SkSVGRenderContext&, const SkSVGNode*);
     ~SkSVGRenderContext();
 
     const SkSVGLengthContext& lengthContext() const { return *fLengthContext; }
@@ -119,6 +120,9 @@ class SkSVGRenderContext {
     // The local computed clip path (not inherited).
     const SkPath* clipPath() const { return fClipPath.getMaybeNull(); }
 
+    // The node being rendered (may be null).
+    const SkSVGNode* node() const { return fNode; }
+
 private:
     // Stack-only
     void* operator new(size_t)                               = delete;
@@ -139,6 +143,8 @@ class SkSVGRenderContext {
 
     // clipPath, if present for the current context (not inherited).
     SkTLazy<SkPath>                               fClipPath;
+
+    const SkSVGNode* fNode;
 };
 
 #endif // SkSVGRenderContext_DEFINED

modules/svg/src/SkSVGDOM.cpp

@@ -593,7 +593,7 @@ void SkSVGDOM::render(SkCanvas* canvas) const {
     if (fRoot) {
         SkSVGLengthContext       lctx(fContainerSize);
         SkSVGPresentationContext pctx;
-        fRoot->render(SkSVGRenderContext(canvas, fIDMapper, lctx, pctx));
+        fRoot->render(SkSVGRenderContext(canvas, fIDMapper, lctx, pctx, nullptr));
     }
 }
 

modules/svg/src/SkSVGNode.cpp

@@ -19,7 +19,7 @@ SkSVGNode::SkSVGNode(SkSVGTag t) : fTag(t) { }
 SkSVGNode::~SkSVGNode() { }
 
 void SkSVGNode::render(const SkSVGRenderContext& ctx) const {
-    SkSVGRenderContext localContext(ctx);
+    SkSVGRenderContext localContext(ctx, this);
 
     if (this->onPrepareToRender(&localContext)) {
         this->onRender(localContext);
@@ -48,6 +48,10 @@ SkPath SkSVGNode::asPath(const SkSVGRenderContext& ctx) const {
     return path;
 }
 
+SkRect SkSVGNode::objectBoundingBox(const SkSVGLengthContext& lctx) const {
+    return this->onObjectBoundingBox(lctx);
+}
+
 bool SkSVGNode::onPrepareToRender(SkSVGRenderContext* ctx) const {
     ctx->applyPresentationAttributes(fPresentationAttributes,
                                      this->hasChildren() ? 0 : SkSVGRenderContext::kLeaf);

modules/svg/src/SkSVGRenderContext.cpp

@@ -317,7 +317,7 @@ SkSVGPresentationContext::SkSVGPresentationContext()
     // Commit initial values to the paint cache.
     SkCanvas fakeCanvas(0, 0);
     SkSVGRenderContext fake(&fakeCanvas, SkSVGIDMapper(), SkSVGLengthContext(SkSize::Make(0, 0)),
-                             *this);
+                             *this, nullptr);
 
     commitToPaint<SkSVGAttribute::kFill>(fInherited, fake, this);
     commitToPaint<SkSVGAttribute::kFillOpacity>(fInherited, fake, this);
@@ -332,24 +332,35 @@ SkSVGPresentationContext::SkSVGPresentationContext()
 SkSVGRenderContext::SkSVGRenderContext(SkCanvas* canvas,
                                        const SkSVGIDMapper& mapper,
                                        const SkSVGLengthContext& lctx,
-                                       const SkSVGPresentationContext& pctx)
+                                       const SkSVGPresentationContext& pctx,
+                                       const SkSVGNode* node)
     : fIDMapper(mapper)
     , fLengthContext(lctx)
     , fPresentationContext(pctx)
     , fCanvas(canvas)
-    , fCanvasSaveCount(canvas->getSaveCount()) {}
+    , fCanvasSaveCount(canvas->getSaveCount())
+    , fNode(node) {}
 
 SkSVGRenderContext::SkSVGRenderContext(const SkSVGRenderContext& other)
     : SkSVGRenderContext(other.fCanvas,
                          other.fIDMapper,
                          *other.fLengthContext,
-                         *other.fPresentationContext) {}
+                         *other.fPresentationContext,
+                         other.fNode) {}
 
 SkSVGRenderContext::SkSVGRenderContext(const SkSVGRenderContext& other, SkCanvas* canvas)
     : SkSVGRenderContext(canvas,
                          other.fIDMapper,
                          *other.fLengthContext,
-                         *other.fPresentationContext) {}
+                         *other.fPresentationContext,
+                         other.fNode) {}
+
+SkSVGRenderContext::SkSVGRenderContext(const SkSVGRenderContext& other, const SkSVGNode* node)
+    : SkSVGRenderContext(other.fCanvas,
+                         other.fIDMapper,
+                         *other.fLengthContext,
+                         *other.fPresentationContext,
+                         node) {}
 
 SkSVGRenderContext::~SkSVGRenderContext() {
     fCanvas->restoreToCount(fCanvasSaveCount);