Issue #1620 - Use Intrinsic Aspect Ratio for Images

https://bugzilla.mozilla.org/show_bug.cgi?id=1547231
https://bugzilla.mozilla.org/show_bug.cgi?id=1559094
https://bugzilla.mozilla.org/show_bug.cgi?id=1633434
https://bugzilla.mozilla.org/show_bug.cgi?id=1565690
https://bugzilla.mozilla.org/show_bug.cgi?id=1602047

Make use of Aspect Ratios in Image frames before Images are loaded.
- Check for width and height HTML properties and create a ratio with them.
- Overwrite HTML size values with actual image dimensions on load.
- Collapse any frames with srcless images.

Comments:
dom/html/nsGenericHTMLElement.cpp:1483
layout/generic/nsImageFrame.cpp:289

4 files changed, 54 insertions, 17 deletions

diff --git a/dom/html/HTMLImageElement.cpp b/dom/html/HTMLImageElement.cpp
index 444c352e2c..d042a9fe6f 100644
--- a/dom/html/HTMLImageElement.cpp
+++ b/dom/html/HTMLImageElement.cpp
@@ -325,7 +325,7 @@ HTMLImageElement::MapAttributesIntoRule(const nsMappedAttributes* aAttributes,
   nsGenericHTMLElement::MapImageAlignAttributeInto(aAttributes, aData);
   nsGenericHTMLElement::MapImageBorderAttributeInto(aAttributes, aData);
   nsGenericHTMLElement::MapImageMarginAttributeInto(aAttributes, aData);
-  nsGenericHTMLElement::MapImageSizeAttributesInto(aAttributes, aData);
+  nsGenericHTMLElement::MapImageSizeAttributesInto(aAttributes, aData, true);
   nsGenericHTMLElement::MapCommonAttributesInto(aAttributes, aData);
 }
 
diff --git a/dom/html/HTMLImageElement.h b/dom/html/HTMLImageElement.h
index bb4a098824..23cac4afb9 100644
--- a/dom/html/HTMLImageElement.h
+++ b/dom/html/HTMLImageElement.h
@@ -196,6 +196,11 @@ public:
     return GetReferrerPolicyAsEnum();
   }
 
+  bool IsAwaitingLoad() const
+  {
+    return !!mPendingImageLoadTask;
+  }
+
   int32_t X();
   int32_t Y();
   // Uses XPCOM GetLowsrc.
diff --git a/dom/html/nsGenericHTMLElement.cpp b/dom/html/nsGenericHTMLElement.cpp
index b52e61ce6e..afc76ee31c 100644
--- a/dom/html/nsGenericHTMLElement.cpp
+++ b/dom/html/nsGenericHTMLElement.cpp
@@ -1449,29 +1449,59 @@ nsGenericHTMLElement::MapImageMarginAttributeInto(const nsMappedAttributes* aAtt
 
 void
 nsGenericHTMLElement::MapImageSizeAttributesInto(const nsMappedAttributes* aAttributes,
-                                                 nsRuleData* aData)
+                                                 nsRuleData* aData,
+                                                 bool aMapAspectRatio)
 {
   if (!(aData->mSIDs & NS_STYLE_INHERIT_BIT(Position)))
     return;
 
+  auto* aWidth = aAttributes->GetAttr(nsGkAtoms::width);
+  auto* aHeight = aAttributes->GetAttr(nsGkAtoms::height);
+
   // width: value
-  nsCSSValue* width = aData->ValueForWidth();
-  if (width->GetUnit() == eCSSUnit_Null) {
-    const nsAttrValue* value = aAttributes->GetAttr(nsGkAtoms::width);
-    if (value && value->Type() == nsAttrValue::eInteger)
-      width->SetFloatValue((float)value->GetIntegerValue(), eCSSUnit_Pixel);
-    else if (value && value->Type() == nsAttrValue::ePercent)
-      width->SetPercentValue(value->GetPercentValue());
+  if (aWidth) {
+    nsCSSValue* cWidth = aData->ValueForWidth();
+    if (cWidth->GetUnit() == eCSSUnit_Null) {
+      if (aWidth->Type() == nsAttrValue::eInteger)
+        cWidth->SetFloatValue((float)aWidth->GetIntegerValue(), eCSSUnit_Pixel);
+      else if (aWidth->Type() == nsAttrValue::ePercent)
+        cWidth->SetPercentValue(aWidth->GetPercentValue());
+    }
   }
 
   // height: value
-  nsCSSValue* height = aData->ValueForHeight();
-  if (height->GetUnit() == eCSSUnit_Null) {
-    const nsAttrValue* value = aAttributes->GetAttr(nsGkAtoms::height);
-    if (value && value->Type() == nsAttrValue::eInteger)
-      height->SetFloatValue((float)value->GetIntegerValue(), eCSSUnit_Pixel); 
-    else if (value && value->Type() == nsAttrValue::ePercent)
-      height->SetPercentValue(value->GetPercentValue());
+  if (aHeight) {
+    nsCSSValue* cHeight = aData->ValueForHeight();
+    if (cHeight->GetUnit() == eCSSUnit_Null) {
+      if (aHeight->Type() == nsAttrValue::eInteger)
+        cHeight->SetFloatValue((float)aHeight->GetIntegerValue(), eCSSUnit_Pixel); 
+      else if (aHeight->Type() == nsAttrValue::ePercent)
+        cHeight->SetPercentValue(aHeight->GetPercentValue());
+    }
+  }
+
+  // 2020-07-15 (RealityRipple) Much of this is a guess based on a few sources.
+  // Please go over this with a fine-tooth comb before production.
+  if (Preferences::GetBool("layout.css.width-and-height-map-to-aspect-ratio.enabled") &&
+      aMapAspectRatio && aWidth && aHeight) {
+    Maybe<double> w;
+    if (aWidth->Type() == nsAttrValue::eInteger) {
+      w.emplace(aWidth->GetIntegerValue());
+    } else if (aWidth->Type() == nsAttrValue::eDoubleValue) {
+      w.emplace(aWidth->GetDoubleValue());
+    }
+
+    Maybe<double> h;
+    if (aHeight->Type() == nsAttrValue::eInteger) {
+      h.emplace(aHeight->GetIntegerValue());
+    } else if (aHeight->Type() == nsAttrValue::eDoubleValue) {
+      h.emplace(aHeight->GetDoubleValue());
+    }
+
+    if (w && h && *w != 0 && *h != 0) {
+      nsCSSValue* aspect_ratio = aData->ValueForAspectRatio();
+      aspect_ratio->SetFloatValue((float(*w) / float(*h)), eCSSUnit_Number);
+    }
   }
 }
 
diff --git a/dom/html/nsGenericHTMLElement.h b/dom/html/nsGenericHTMLElement.h
index c9169df117..8412ea0dc8 100644
--- a/dom/html/nsGenericHTMLElement.h
+++ b/dom/html/nsGenericHTMLElement.h
@@ -702,10 +702,12 @@ public:
    *
    * @param aAttributes the list of attributes to map
    * @param aData the returned rule data [INOUT]
+   * @param aMapAspectRatio map width and height attributes on aspect-ratio
    * @see GetAttributeMappingFunction
    */
   static void MapImageSizeAttributesInto(const nsMappedAttributes* aAttributes,
-                                         nsRuleData* aData);
+                                         nsRuleData* aData,
+                                         bool = false);
   /**
    * Helper to map the background attribute
    * into a style struct.