[skottie] Add support for text grouping alignment

AE allows relative adjustments for text animator transform anchor
points [1].

[1] https://helpx.adobe.com/after-effects/using/animating-text.html#text_anchor_point_properties

Change-Id: If98d6b522e73a768ed2358d918867d2aefd09071
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/274044
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Florin Malita <fmalita@chromium.org>

modules/skottie/src/text/TextAdapter.cpp

@@ -65,6 +65,12 @@ sk_sp<TextAdapter> TextAdapter::Make(const skjson::ObjectValue& jlayer,
     auto adapter = sk_sp<TextAdapter>(new TextAdapter(std::move(fontmgr), std::move(logger)));
     adapter->bind(*abuilder, jd, &adapter->fText.fCurrentValue);
 
+    // "More options"
+    if (const skjson::ObjectValue* jm = (*jt)["m"]) {
+        adapter->bind(*abuilder, (*jm)["a"], &adapter->fGroupingAlignment);
+    }
+
+    // Animators
     if (const skjson::ArrayValue* janimators = (*jt)["a"]) {
         adapter->fAnimators.reserve(janimators->size());
 
@@ -298,6 +304,9 @@ void TextAdapter::onSync() {
         animator->modulateProps(fMaps, buf);
     }
 
+    const auto grouping_alignment =
+            ValueTraits<VectorValue>::As<SkVector>(fGroupingAlignment) * .01f; // percentage
+
     // Finally, push all props to their corresponding fragment.
     for (const auto& line_span : fMaps.fLinesMap) {
         float line_tracking = 0;
@@ -308,7 +317,7 @@ void TextAdapter::onSync() {
         for (size_t i = line_span.fOffset; i < line_span.fOffset + line_span.fCount; ++i) {
             const auto& props = buf[i].props;
             const auto& frag  = fFragments[i];
-            this->pushPropsToFragment(props, frag);
+            this->pushPropsToFragment(props, frag, grouping_alignment);
 
             line_tracking += props.tracking;
             line_has_tracking |= !SkScalarNearlyZero(props.tracking);
@@ -320,21 +329,33 @@ void TextAdapter::onSync() {
     }
 }
 
+SkV2 TextAdapter::fragmentAnchorPoint(const FragmentRec& rec,
+                                      const SkVector& group_alignment) const {
+    // TODO: implement word/line/paragraph alignment options.
+
+    // Character alignment: origin is at [advance/2,0] (mid-advance, baseline)
+    const SkV2 ap = { rec.fAdvance * 0.5f, 0 };
+
+    // Group alignment is an origin adjustment relative to the
+    // ascent box [0, ascent, advance, 0]
+    return ap + SkV2{group_alignment.fX * (ap.x -           0),
+                     group_alignment.fY * (ap.y - rec.fAscent)};
+}
+
 void TextAdapter::pushPropsToFragment(const TextAnimator::ResolvedProps& props,
-                                      const FragmentRec& rec) const {
-    // For now hard-code to default center/baseline.
-    // TODO: add support for grouping/adjustments.
-    const SkV3 anchor_point = { rec.fAdvance * 0.5f, 0, 0 };
+                                      const FragmentRec& rec,
+                                      const SkVector& grouping_alignment) const {
+    const auto anchor_point = this->fragmentAnchorPoint(rec, grouping_alignment);
 
     rec.fMatrixNode->setMatrix(
-                SkM44::Translate(anchor_point.x + props.position.x + rec.fOrigin.x(),
-                                 anchor_point.y + props.position.y + rec.fOrigin.y(),
-                                 anchor_point.z + props.position.z)
+                SkM44::Translate(props.position.x + rec.fOrigin.x() + anchor_point.x,
+                                 props.position.y + rec.fOrigin.y() + anchor_point.y,
+                                 props.position.z)
               * SkM44::Rotate({ 1, 0, 0 }, SkDegreesToRadians(props.rotation.x))
               * SkM44::Rotate({ 0, 1, 0 }, SkDegreesToRadians(props.rotation.y))
               * SkM44::Rotate({ 0, 0, 1 }, SkDegreesToRadians(props.rotation.z))
               * SkM44::Scale(props.scale.x, props.scale.y, props.scale.z)
-              * SkM44::Translate(-anchor_point.x, -anchor_point.y, -anchor_point.z));
+              * SkM44::Translate(-anchor_point.x, -anchor_point.y, 0));
 
     const auto scale_alpha = [](SkColor c, float o) {
         return SkColorSetA(c, SkScalarRoundToInt(o * SkColorGetA(c)));

modules/skottie/src/text/TextAdapter.h

@@ -57,17 +57,20 @@ private:
                                      fAscent;  // ^
     };
 
-    uint32_t shaperFlags() const;
     void reshape();
     void addFragment(const Shaper::Fragment&);
     void buildDomainMaps(const Shaper::Result&);
 
-    void pushPropsToFragment(const TextAnimator::ResolvedProps&, const FragmentRec&) const;
+    void pushPropsToFragment(const TextAnimator::ResolvedProps&, const FragmentRec&,
+                             const SkVector&) const;
 
     void adjustLineTracking(const TextAnimator::ModulatorBuffer&,
                             const TextAnimator::DomainSpan&,
                             float line_tracking) const;
 
+    SkV2 fragmentAnchorPoint(const FragmentRec&, const SkVector&) const;
+    uint32_t shaperFlags() const;
+
     const sk_sp<sksg::Group>         fRoot;
     const sk_sp<SkFontMgr>           fFontMgr;
     sk_sp<Logger>                    fLogger;
@@ -95,6 +98,8 @@ private:
     };
 
     TextValueTracker fText;
+    VectorValue      fGroupingAlignment;
+
     bool             fHasBlurAnimator     : 1,
                      fRequiresAnchorPoint : 1;
 };