[SVGDom] Initial linear gradient support

experimental/svg/model/SkSVGLinearGradient.cpp

Index: experimental/svg/model/SkSVGLinearGradient.cpp
diff --git a/experimental/svg/model/SkSVGLinearGradient.cpp b/experimental/svg/model/SkSVGLinearGradient.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..ed4942b0c7e6d238f536c9ce8185a0fa5b5cbc5a
--- /dev/null
+++ b/experimental/svg/model/SkSVGLinearGradient.cpp
@@ -0,0 +1,117 @@
+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkGradientShader.h"
+#include "SkSVGLinearGradient.h"
+#include "SkSVGRenderContext.h"
+#include "SkSVGStop.h"
+#include "SkSVGValue.h"
+
+SkSVGLinearGradient::SkSVGLinearGradient() : INHERITED(SkSVGTag::kLinearGradient) {}
+
+void SkSVGLinearGradient::setHref(const SkSVGStringType& href) {
+    fHref = std::move(href);
+}
+
+void SkSVGLinearGradient::setX1(const SkSVGLength& x1) {
+    fX1 = x1;
+}
+
+void SkSVGLinearGradient::setY1(const SkSVGLength& y1) {
+    fY1 = y1;
+}
+
+void SkSVGLinearGradient::setX2(const SkSVGLength& x2) {
+    fX2 = x2;
+}
+
+void SkSVGLinearGradient::setY2(const SkSVGLength& y2) {
+    fY2 = y2;
+}
+
+void SkSVGLinearGradient::onSetAttribute(SkSVGAttribute attr, const SkSVGValue& v) {
+    switch (attr) {
+    case SkSVGAttribute::kHref:
+        if (const auto* href = v.as<SkSVGStringValue>()) {
+            this->setHref(*href);
+        }
+        break;
+    case SkSVGAttribute::kX1:
+        if (const auto* x1 = v.as<SkSVGLengthValue>()) {
+            this->setX1(*x1);
+        }
+        break;
+    case SkSVGAttribute::kY1:
+        if (const auto* y1 = v.as<SkSVGLengthValue>()) {
+            this->setY1(*y1);
+        }
+        break;
+    case SkSVGAttribute::kX2:
+        if (const auto* x2 = v.as<SkSVGLengthValue>()) {
+            this->setX2(*x2);
+        }
+        break;
+    case SkSVGAttribute::kY2:
+        if (const auto* y2 = v.as<SkSVGLengthValue>()) {
+            this->setY2(*y2);
+        }
+        break;
+    default:
+        this->INHERITED::onSetAttribute(attr, v);
+    }
+}
+
+// https://www.w3.org/TR/SVG/pservers.html#LinearGradientElementHrefAttribute
+void SkSVGLinearGradient::collectColorStops(const SkSVGRenderContext& ctx,
+                                            SkSTArray<2, SkScalar, true>* pos,
+                                            SkSTArray<2, SkColor, true>* 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));
+    }
+

[robertphillips, 2016/09/12 19:31:52]

Shouldn't this test be more like:

if ((pos->count() < 2 || colors->count() < 2) && !....

?

[f(malita), 2016/09/12 19:52:09]

pos->count should always match colors->count because we always insert in
lock-step.  Added an assert to document.

Then for count == 1, I think we don't need to recurse:

a) "if one stop is defined, then paint with the solid color fill using the color
defined for that gradient stop."
(https://www.w3.org/TR/SVG/pservers.html#StopOpacityProperty)

b) "if this element has no defined gradient stops, and the referenced element
does (possibly due to its own ‘xlink:href’ attribute), then this element
inherits the gradient stop from the referenced element. Inheritance can be
indirect to an arbitrary level;"
(https://www.w3.org/TR/SVG/pservers.html#LinearGradientElementHrefAttribute)

Sounds like they want to inherit only for an empty list.

+    if (pos->empty() && !fHref.value().isEmpty()) {
+        const auto* ref = ctx.findNodeById(fHref);
+        if (ref && ref->tag() == SkSVGTag::kLinearGradient) {
+            static_cast<const SkSVGLinearGradient*>(ref)->collectColorStops(ctx, pos, colors);
+        }
+    }
+}
+
+bool SkSVGLinearGradient::onAsPaint(const SkSVGRenderContext& ctx, SkPaint* paint) const {
+    const auto& lctx = ctx.lengthContext();
+    const auto x1 = lctx.resolve(fX1, SkSVGLengthContext::LengthType::kHorizontal);
+    const auto y1 = lctx.resolve(fY1, SkSVGLengthContext::LengthType::kVertical);
+    const auto x2 = lctx.resolve(fX2, SkSVGLengthContext::LengthType::kHorizontal);
+    const auto y2 = lctx.resolve(fY2, SkSVGLengthContext::LengthType::kVertical);
+
+    const SkPoint pts[2] = { {x1, y1}, {x2, y2}};
+    SkSTArray<2, SkColor , true> colors;
+    SkSTArray<2, SkScalar, true> pos;
+
+    this->collectColorStops(ctx, &pos, &colors);
+    // TODO:
+    //       * stop (lazy?) sorting
+    //       * href loop detection
+    //       * href attribute inheritance (not just color stops)
+    //       * spreadMethods support
+    //       * objectBoundingBox units support
+
+    paint->setShader(SkGradientShader::MakeLinear(pts, colors.begin(), pos.begin(), colors.count(),
+                                                  SkShader::kClamp_TileMode));
+    return true;
+}