Document SVGAnimationElement::CheckAnimationParameters()

And its companion SVGAnimationElement::CalculateValuesAnimation().

Bug: 998526
Change-Id: I3895dc070d319f1cefa489e061a598b18a88cf98
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1871509
Commit-Queue: Fredrik Söderquist <fs@opera.com>
Reviewed-by: Stephen Chenney <schenney@chromium.org>
Cr-Commit-Position: refs/heads/master@{#708119}

third_party/blink/renderer/core/svg/svg_animation_element.cc

@@ -522,19 +522,27 @@ bool SVGAnimationElement::CalculateValuesAnimation() {
   if (values_.IsEmpty())
     return false;
   CalcMode calc_mode = GetCalcMode();
+  // For 'values' animations, there should be exactly as many 'keyTimes' as
+  // 'values'.
   if (calc_mode != kCalcModePaced &&
-      FastHasAttribute(svg_names::kKeyTimesAttr) &&
       !FastHasAttribute(svg_names::kKeyPointsAttr) &&
+      FastHasAttribute(svg_names::kKeyTimesAttr) &&
       values_.size() != KeyTimes().size())
     return false;
+  // If 'keyTimes' is specified its last value should be 1 (and the first 0)
+  // unless 'calcMode' is 'discrete'.
   if (calc_mode != kCalcModeDiscrete && !KeyTimes().IsEmpty() &&
       KeyTimes().back() != 1)
     return false;
+  // If 'calcMode' is 'spline', there should be one less spline than there are
+  // 'keyPoints' or 'values'.
   if (calc_mode == kCalcModeSpline) {
     if ((key_splines_.IsEmpty() || key_splines_.size() != values_.size() - 1) &&
         key_splines_.size() != key_points_.size() - 1)
       return false;
   }
+  // If 'keyPoints' is specified it should have the same amount of points as
+  // 'keyTimes', and at least two points.
   if (FastHasAttribute(svg_names::kKeyPointsAttr) &&
       (KeyTimes().size() < 2 || KeyTimes().size() != key_points_.size()))
     return false;
@@ -554,12 +562,16 @@ bool SVGAnimationElement::CheckAnimationParameters() {
     return false;
 
   // These validations are appropriate for all animation modes.
+  // If 'keyPoints' is specified it should have the same amount of points as
+  // 'keyTimes'.
   if (FastHasAttribute(svg_names::kKeyPointsAttr) &&
       KeyTimes().size() != key_points_.size())
     return false;
 
   CalcMode calc_mode = GetCalcMode();
   if (calc_mode == kCalcModeSpline) {
+    // If 'calcMode' is 'spline', there should be one less spline than there
+    // are 'keyTimes' or 'keyPoints' - or 'values' if it is used.
     if (key_splines_.IsEmpty() ||
         (FastHasAttribute(svg_names::kKeyPointsAttr) &&
          key_splines_.size() != key_points_.size() - 1) ||
@@ -570,13 +582,17 @@ bool SVGAnimationElement::CheckAnimationParameters() {
       return false;
   }
 
-  if ((animation_mode == kFromToAnimation ||
-       animation_mode == kFromByAnimation || animation_mode == kToAnimation ||
-       animation_mode == kByAnimation) &&
-      (FastHasAttribute(svg_names::kKeyTimesAttr) &&
-       FastHasAttribute(svg_names::kKeyPointsAttr) &&
-       (KeyTimes().size() < 2 || KeyTimes().size() != key_points_.size())))
-    return false;
+  if (animation_mode == kFromToAnimation ||
+      animation_mode == kFromByAnimation || animation_mode == kToAnimation ||
+      animation_mode == kByAnimation) {
+    if (FastHasAttribute(svg_names::kKeyTimesAttr)) {
+      // If 'keyPoints' is specified it should have the same amount of points
+      // as 'keyTimes', and at least two points.
+      if (FastHasAttribute(svg_names::kKeyPointsAttr) &&
+          (KeyTimes().size() < 2 || KeyTimes().size() != key_points_.size()))
+        return false;
+    }
+  }
   const String& from = FromValue();
   const String& to = ToValue();
   const String& by = ByValue();
@@ -595,10 +611,14 @@ bool SVGAnimationElement::CheckAnimationParameters() {
   if (animation_mode == kValuesAnimation)
     return CalculateValuesAnimation();
   if (animation_mode == kPathAnimation) {
-    return calc_mode == kCalcModePaced ||
-           !(FastHasAttribute(svg_names::kKeyPointsAttr) &&
-             (KeyTimes().size() < 2 ||
-              KeyTimes().size() != key_points_.size()));
+    if (calc_mode == kCalcModePaced)
+      return true;
+    // If 'keyPoints' is specified it should have the same amount of points as
+    // 'keyTimes', and at least two points.
+    if (FastHasAttribute(svg_names::kKeyPointsAttr) &&
+        (KeyTimes().size() < 2 || KeyTimes().size() != key_points_.size()))
+      return false;
+    return true;
   }
   return false;
 }