[SVGDom] Factor out common gradient logic

In preparation of radial gradient support, move common logic into an
abstract base class (SkSVGGradient).

Change-Id: Ie5361048ca8fddd9070c573c8daef0d0f57dc95e
Reviewed-on: https://skia-review.googlesource.com/57108
Commit-Queue: Florin Malita <fmalita@chromium.org>
Reviewed-by: Robert Phillips <robertphillips@google.com>

1 files changed, 99 insertions, 0 deletions

diff --git a/experimental/svg/model/SkSVGGradient.cpp b/experimental/svg/model/SkSVGGradient.cpp
new file mode 100644
index 0000000000..fbd5f77590
--- /dev/null
+++ b/experimental/svg/model/SkSVGGradient.cpp
@@ -0,0 +1,99 @@
+/*
+ * Copyright 2017 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkSVGGradient.h"
+#include "SkSVGRenderContext.h"
+#include "SkSVGStop.h"
+#include "SkSVGValue.h"
+
+void SkSVGGradient::setHref(const SkSVGStringType& href) {
+    fHref = std::move(href);
+}
+
+void SkSVGGradient::setGradientTransform(const SkSVGTransformType& t) {
+    fGradientTransform = t;
+}
+
+void SkSVGGradient::setSpreadMethod(const SkSVGSpreadMethod& spread) {
+    fSpreadMethod = spread;
+}
+
+void SkSVGGradient::onSetAttribute(SkSVGAttribute attr, const SkSVGValue& v) {
+    switch (attr) {
+    case SkSVGAttribute::kGradientTransform:
+        if (const auto* t = v.as<SkSVGTransformValue>()) {
+            this->setGradientTransform(*t);
+        }
+        break;
+    case SkSVGAttribute::kHref:
+        if (const auto* href = v.as<SkSVGStringValue>()) {
+            this->setHref(*href);
+        }
+        break;
+    case SkSVGAttribute::kSpreadMethod:
+        if (const auto* spread = v.as<SkSVGSpreadMethodValue>()) {
+            this->setSpreadMethod(*spread);
+        }
+        break;
+    default:
+        this->INHERITED::onSetAttribute(attr, v);
+    }
+}
+
+// https://www.w3.org/TR/SVG/pservers.html#LinearGradientElementHrefAttribute
+void SkSVGGradient::collectColorStops(const SkSVGRenderContext& ctx,
+                                      StopPositionArray* pos,
+                                      StopColorArray* colors) const {
+    // Used to resolve percentage offsets.
+    const SkSVGLengthContext ltx(SkSize::Make(1, 1));
+
+    for (const auto& child : fChildren) {
+        if (child->tag() != SkSVGTag::kStop) {
+            continue;
+        }
+
+        const auto& stop = static_cast<const SkSVGStop&>(*child);
+        colors->push_back(SkColorSetA(stop.stopColor(),
+                                      SkScalarRoundToInt(stop.stopOpacity() * 255)));
+        pos->push_back(SkTPin(ltx.resolve(stop.offset(), SkSVGLengthContext::LengthType::kOther),
+                              0.f, 1.f));
+    }
+
+    SkASSERT(colors->count() == pos->count());
+
+    if (pos->empty() && !fHref.value().isEmpty()) {
+        const auto* ref = ctx.findNodeById(fHref);
+        if (ref && ref->tag() == SkSVGTag::kLinearGradient) {
+            static_cast<const SkSVGGradient*>(ref)->collectColorStops(ctx, pos, colors);
+        }
+    }
+}
+
+bool SkSVGGradient::onAsPaint(const SkSVGRenderContext& ctx, SkPaint* paint) const {
+    StopColorArray colors;
+    StopPositionArray pos;
+
+    this->collectColorStops(ctx, &pos, &colors);
+
+    // TODO:
+    //       * stop (lazy?) sorting
+    //       * href loop detection
+    //       * href attribute inheritance (not just color stops)
+    //       * objectBoundingBox units support
+
+    static_assert(static_cast<SkShader::TileMode>(SkSVGSpreadMethod::Type::kPad) ==
+                  SkShader::kClamp_TileMode, "SkSVGSpreadMethod::Type is out of sync");
+    static_assert(static_cast<SkShader::TileMode>(SkSVGSpreadMethod::Type::kRepeat) ==
+                  SkShader::kRepeat_TileMode, "SkSVGSpreadMethod::Type is out of sync");
+    static_assert(static_cast<SkShader::TileMode>(SkSVGSpreadMethod::Type::kReflect) ==
+                  SkShader::kMirror_TileMode, "SkSVGSpreadMethod::Type is out of sync");
+    const auto tileMode = static_cast<SkShader::TileMode>(fSpreadMethod.type());
+
+    paint->setShader(this->onMakeShader(ctx, colors.begin(), pos.begin(), colors.count(), tileMode,
+                                        fGradientTransform.value()));
+    return true;
+}