[iOS] Attempt to fix text-anchor subtree advance/extent calculation

Related to
https://github.com/react-native-community/react-native-svg/issues/600
https://github.com/react-native-community/react-native-svg/issues/570

ios/Text/RNSVGTSpan.m

@@ -100,6 +100,65 @@ static CGFloat RNSVGTSpan_radToDeg = 180 / (CGFloat)M_PI;
     return path;
 }
 
+- (CGFloat)getSubtreeTextChunksTotalAdvance
+{
+    CGFloat advance = 0;
+
+    NSString *str = self.content;
+    if (!str) {
+        for (UIView *node in self.subviews) {
+            if ([node isKindOfClass:[RNSVGText class]]) {
+                RNSVGText *text = (RNSVGText*)node;
+                advance += [text getSubtreeTextChunksTotalAdvance];
+            }
+        }
+        return advance;
+    }
+
+    // Create a dictionary for this font
+    CTFontRef fontRef = [self getFontFromContext];
+    RNSVGGlyphContext* gc = [self.textRoot getGlyphContext];
+    RNSVGFontData* font = [gc getFont];
+
+    CGFloat letterSpacing = font->letterSpacing;
+    bool autoKerning = !font->manualKerning;
+
+    bool allowOptionalLigatures = letterSpacing == 0 && font->fontVariantLigatures == RNSVGFontVariantLigaturesNormal;
+
+    NSMutableDictionary *attrs = [[NSMutableDictionary alloc] init];
+
+    NSNumber *lig = [NSNumber numberWithInt:allowOptionalLigatures ? 2 : 1];
+    attrs[NSLigatureAttributeName] = lig;
+    CFDictionaryRef attributes;
+    if (fontRef != nil) {
+        attrs[NSFontAttributeName] = (__bridge id)fontRef;
+    }
+    if (!autoKerning) {
+        NSNumber *noAutoKern = [NSNumber numberWithFloat:0.0f];
+
+#if DTCORETEXT_SUPPORT_NS_ATTRIBUTES
+        if (___useiOS6Attributes)
+        {
+            [attrs setObject:noAutoKern forKey:NSKernAttributeName];
+        }
+        else
+#endif
+        {
+            [attrs setObject:noAutoKern forKey:(id)kCTKernAttributeName];
+        }
+    }
+
+    attributes = (__bridge CFDictionaryRef)attrs;
+
+    CFStringRef string = (__bridge CFStringRef)str;
+    CFAttributedStringRef attrString = CFAttributedStringCreate(kCFAllocatorDefault, string, attributes);
+    CTLineRef line = CTLineCreateWithAttributedString(attrString);
+
+    CGRect textBounds = CTLineGetBoundsWithOptions(line, 0);
+    CGFloat textMeasure = CGRectGetWidth(textBounds);
+    return textMeasure;
+}
+
 - (CGPathRef)getLinePath:(NSString *)str context:(CGContextRef)context
 {
     // Create a dictionary for this font
@@ -292,8 +351,8 @@ static CGFloat RNSVGTSpan_radToDeg = 180 / (CGFloat)M_PI;
      attributes, such as a ‘dx’ attribute value on a ‘tspan’ element.
      */
     enum RNSVGTextAnchor textAnchor = font->textAnchor;
-    CGRect textBounds = CTLineGetBoundsWithOptions(line, 0);
-    CGFloat textMeasure = CGRectGetWidth(textBounds);
+    RNSVGText *anchorRoot = [self getTextAnchorRoot];
+    CGFloat textMeasure = [anchorRoot getSubtreeTextChunksTotalAdvance];
     CGFloat offset = [RNSVGTSpan getTextAnchorOffset:textAnchor width:textMeasure];
 
     bool hasTextPath = textPath != nil;

ios/Text/RNSVGText.h

@@ -23,5 +23,7 @@
 
 - (CGPathRef)getGroupPath:(CGContextRef)context;
 - (CTFontRef)getFontFromContext;
+- (CGFloat)getSubtreeTextChunksTotalAdvance;
+- (RNSVGText*)getTextAnchorRoot;
 
 @end

ios/Text/RNSVGText.m

@@ -18,6 +18,7 @@
     RNSVGGlyphContext *_glyphContext;
     NSString *_alignmentBaseline;
     NSString *_baselineShift;
+    CGFloat cachedAdvance;
 }
 
 - (void)invalidate
@@ -25,6 +26,7 @@
     if (self.dirty || self.merging) {
         return;
     }
+    cachedAdvance = NAN;
     [super invalidate];
     [self clearChildCache];
 }
@@ -248,4 +250,43 @@
     return [[self.textRoot getGlyphContext] getGlyphFont];
 }
 
+- (RNSVGText*)getTextAnchorRoot
+{
+    RNSVGGlyphContext* gc = [self.textRoot getGlyphContext];
+    RNSVGFontData* font = [gc getFont];
+    enum RNSVGTextAnchor textAnchor = font->textAnchor;
+    if (textAnchor == RNSVGTextAnchorStart) {
+        return self;
+    }
+    UIView* parent = [self superview];
+    if ([parent isKindOfClass:[RNSVGText class]]) {
+        RNSVGText *parentText = (RNSVGText*)parent;
+        RNSVGGlyphContext* gc = [parentText.textRoot getGlyphContext];
+        RNSVGFontData* font = [gc getFont];
+        enum RNSVGTextAnchor textAnchor = font->textAnchor;
+        if (textAnchor == RNSVGTextAnchorStart) {
+            return self;
+        } else {
+            return [parentText getTextAnchorRoot];
+        }
+    }
+    return self;
+}
+
+- (CGFloat)getSubtreeTextChunksTotalAdvance
+{
+    if (!isnan(cachedAdvance)) {
+        return cachedAdvance;
+    }
+    CGFloat advance = 0;
+    for (UIView *node in self.subviews) {
+        if ([node isKindOfClass:[RNSVGText class]]) {
+            RNSVGText *text = (RNSVGText*)node;
+            advance += [text getSubtreeTextChunksTotalAdvance];
+        }
+    }
+    cachedAdvance = advance;
+    return advance;
+}
+
 @end