[svg] New layer for image filter if one is set

Prior to rendering a node, check the filter presentation attribute and
create a new canvas layer with a corresponding SkImageFilter set.

Also added the computation of the filter effect region and added a naive
(and incomplete) construction of the image filter DAG for a
<filter> element.

Bug: skia:10841
Change-Id: Ie94299757e059c39540ad316cddf438df5726d97
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/330619
Commit-Queue: Tyler Denniston <tdenniston@google.com>
Reviewed-by: Florin Malita <fmalita@chromium.org>

modules/svg/include/SkSVGFilter.h

@@ -17,6 +17,8 @@ public:
 
     static sk_sp<SkSVGFilter> Make() { return sk_sp<SkSVGFilter>(new SkSVGFilter()); }
 
+    sk_sp<SkImageFilter> buildFilterDAG(const SkSVGRenderContext&) const;
+
     SVG_ATTR(X, SkSVGLength, SkSVGLength(-10, SkSVGLength::Unit::kPercentage))
     SVG_ATTR(Y, SkSVGLength, SkSVGLength(-10, SkSVGLength::Unit::kPercentage))
     SVG_ATTR(Width, SkSVGLength, SkSVGLength(120, SkSVGLength::Unit::kPercentage))
@@ -28,6 +30,8 @@ public:
 private:
     SkSVGFilter() : INHERITED(SkSVGTag::kFilter) {}
 
+    SkRect resolveFilterRegion(const SkSVGRenderContext&) const;
+
     void onSetAttribute(SkSVGAttribute, const SkSVGValue&) override;
 
     using INHERITED = SkSVGHiddenContainer;

modules/svg/include/SkSVGRenderContext.h

@@ -130,6 +130,7 @@ private:
     SkSVGRenderContext& operator=(const SkSVGRenderContext&) = delete;
 
     void applyOpacity(SkScalar opacity, uint32_t flags);
+    void applyFilter(const SkSVGFilterType&);
     void applyClip(const SkSVGClip&);
     void updatePaintsWithCurrentColor(const SkSVGPresentationAttributes&);
 

modules/svg/src/SkSVGFilter.cpp

@@ -43,3 +43,41 @@ void SkSVGFilter::onSetAttribute(SkSVGAttribute attr, const SkSVGValue& v) {
             this->INHERITED::onSetAttribute(attr, v);
     }
 }
+
+SkRect SkSVGFilter::resolveFilterRegion(const SkSVGRenderContext& ctx) const {
+    const SkSVGLengthContext lctx =
+            fFilterUnits.type() == SkSVGObjectBoundingBoxUnits::Type::kObjectBoundingBox
+                    ? SkSVGLengthContext({1, 1})
+                    : ctx.lengthContext();
+
+    SkRect filterRegion = lctx.resolveRect(fX, fY, fWidth, fHeight);
+    if (fFilterUnits.type() == SkSVGObjectBoundingBoxUnits::Type::kObjectBoundingBox) {
+        SkASSERT(ctx.node());
+        const SkRect objBounds = ctx.node()->objectBoundingBox(ctx);
+        filterRegion = SkRect::MakeXYWH(objBounds.fLeft + filterRegion.fLeft * objBounds.fLeft,
+                                        objBounds.fTop + filterRegion.fTop * objBounds.fTop,
+                                        filterRegion.width() * objBounds.width(),
+                                        filterRegion.height() * objBounds.height());
+    }
+
+    return filterRegion;
+}
+
+sk_sp<SkImageFilter> SkSVGFilter::buildFilterDAG(const SkSVGRenderContext& ctx) const {
+    sk_sp<SkImageFilter> filter;
+    SkSVGFilterContext fctx(resolveFilterRegion(ctx));
+    for (const auto& child : fChildren) {
+        if (!SkSVGFe::IsFilterElement(child)) {
+            continue;
+        }
+
+        const auto& feNode = static_cast<const SkSVGFe&>(*child);
+        sk_sp<SkImageFilter> imageFilter = feNode.makeImageFilter(ctx, &fctx);
+        if (imageFilter) {
+            // TODO: there are specific composition rules that need to be followed
+            filter = SkImageFilters::Compose(imageFilter, filter);
+        }
+    }
+
+    return filter;
+}

modules/svg/src/SkSVGRenderContext.cpp

@@ -8,10 +8,12 @@
 #include "modules/svg/include/SkSVGRenderContext.h"
 
 #include "include/core/SkCanvas.h"
+#include "include/core/SkImageFilter.h"
 #include "include/core/SkPath.h"
 #include "include/effects/SkDashPathEffect.h"
 #include "include/private/SkTo.h"
 #include "modules/svg/include/SkSVGAttribute.h"
+#include "modules/svg/include/SkSVGFilter.h"
 #include "modules/svg/include/SkSVGNode.h"
 #include "modules/svg/include/SkSVGTypes.h"
 
@@ -430,6 +432,11 @@ void SkSVGRenderContext::applyPresentationAttributes(const SkSVGPresentationAttr
     if (auto* clip = attrs.fClipPath.getMaybeNull()) {
         this->applyClip(*clip);
     }
+
+    // TODO: when both a filter and opacity are present, we can apply both with a single layer
+    if (auto* filter = attrs.fFilter.getMaybeNull()) {
+        this->applyFilter(*filter);
+    }
 }
 
 void SkSVGRenderContext::applyOpacity(SkScalar opacity, uint32_t flags) {
@@ -462,6 +469,26 @@ void SkSVGRenderContext::applyOpacity(SkScalar opacity, uint32_t flags) {
     }
 }
 
+void SkSVGRenderContext::applyFilter(const SkSVGFilterType& filter) {
+    if (filter.type() != SkSVGFilterType::Type::kIRI) {
+        return;
+    }
+
+    const auto node = this->findNodeById(filter.iri());
+    if (!node || node->tag() != SkSVGTag::kFilter) {
+        return;
+    }
+
+    const SkSVGFilter* filterNode = reinterpret_cast<const SkSVGFilter*>(node.get());
+    sk_sp<SkImageFilter> imageFilter = filterNode->buildFilterDAG(*this);
+    if (imageFilter) {
+        SkPaint filterPaint;
+        filterPaint.setImageFilter(imageFilter);
+        // Balanced in the destructor, via restoreToCount().
+        fCanvas->saveLayer(nullptr, &filterPaint);
+    }
+}
+
 void SkSVGRenderContext::saveOnce() {
     // The canvas only needs to be saved once, per local SkSVGRenderContext.
     if (fCanvas->getSaveCount() == fCanvasSaveCount) {