MTRowView.m

#include "MTRowView.h"
#include <stdatomic.h>

typedef struct hspan_t {
  volatile _Atomic(int32_t) retain_count;
  CGFloat x,y,width;
} hspan_t;

static hspan_t* hspan_retain(CFAllocatorRef allocator,hspan_t* span) {
  atomic_fetch_add(&span->retain_count, 1);
  return span;
}
static void hspan_release(CFAllocatorRef allocator,hspan_t* span) {
  if(atomic_fetch_add(&span->retain_count, 1)==0){free(span);}
}

@implementation MTRowView
-(id)init {
  if((self=[super init])){
    bgMap=CFDictionaryCreateMutable(NULL,0,
     &kCFTypeDictionaryKeyCallBacks,
     &kCFTypeDictionaryValueCallBacks);
    stMap=CFDictionaryCreateMutable(NULL,0,
     &kCFTypeDictionaryKeyCallBacks,
     &kCFTypeDictionaryValueCallBacks);
    self.clearsContextBeforeDrawing=NO;
    self.opaque=YES;
  }
  return self;
}
-(void)renderString:(CFAttributedStringRef)string withBGColor:(CGColorRef)_bgColor  {
  if(bgColor!=_bgColor){
    CGColorRelease(bgColor);
    bgColor=CGColorRetain(_bgColor);
  }
  if(ctLine){
    CFRelease(ctLine);
    CFDictionaryRemoveAllValues(bgMap);
    CFDictionaryRemoveAllValues(stMap);
  }
  ctLine=CTLineCreateWithAttributedString(string);
  CFArrayRef runs=CTLineGetGlyphRuns(ctLine);
  CFIndex nruns=CFArrayGetCount(runs),i;
  CGFloat x=0,y=0;
  CFMutableDictionaryRef colormap[]={bgMap,stMap};
  const int nmaps=sizeof(colormap)/sizeof(CFDictionaryRef);
  for (i=0;i<nruns;i++){
    CTRunRef run=CFArrayGetValueAtIndex(runs,i);
    CGFloat ascent,width=CTRunGetTypographicBounds(run,
     CFRangeMake(0,0),&ascent,NULL,NULL);
    CFDictionaryRef attr=CTRunGetAttributes(run);
    const void* colorkey[]={
     CFDictionaryGetValue(attr,kMTBackgroundColorAttributeName),
     CFDictionaryGetValue(attr,kMTStrikethroughColorAttributeName)};
    hspan_t* span=NULL;
    int j;
    for (j=0;j<nmaps;j++){
      const void* key=colorkey[j];
      if(!key){continue;}
      CFMutableArrayRef spans=(void*)CFDictionaryGetValue(colormap[j],key);
      if(!spans){
        spans=CFArrayCreateMutable(NULL,0,&(CFArrayCallBacks){
         .retain=(CFArrayRetainCallBack)hspan_retain,
         .release=(CFArrayReleaseCallBack)hspan_release});
        CFDictionaryAddValue(colormap[j],key,spans);
        CFRelease(spans);
      }
      if(!span){
        span=malloc(sizeof(hspan_t));
        span->retain_count=0;// CFArray will retain it
        span->x=x;
        span->width=width;
      }
      // calculate strikethrough position if needed
      if(j==1) span->y=ascent-CTFontGetXHeight(
       CFDictionaryGetValue(attr,kCTFontAttributeName))/2;
      CFArrayAppendValue(spans,span);
    }
    x+=width;
    y+=ascent;
  }
  lineAscent=y/nruns;
  [self setNeedsDisplay];
}
-(void)drawRect:(CGRect)drawRect {
  CGContextRef context=UIGraphicsGetCurrentContext();
  CGContextSetFillColorWithColor(context,bgColor);
  CGContextFillRect(context,drawRect);
  CGFloat xmin=CGRectGetMinX(drawRect),xmax=CGRectGetMaxX(drawRect);
  CFIndex nbg=CFDictionaryGetCount(bgMap);
  if(nbg){// draw background rectangles as needed
    const void** keys=malloc(nbg*sizeof(CGColorRef));
    const void** values=malloc(nbg*sizeof(CFArrayRef));
    CFDictionaryGetKeysAndValues(bgMap,keys,values);
    CFIndex i;
    for (i=0;i<nbg;i++){
      CFIndex nvalues=CFArrayGetCount(values[i]),nrects=0,j;
      CGRect* rects=malloc(nvalues*sizeof(CGRect));
      for (j=0;j<nvalues;j++){
        hspan_t* span=(hspan_t*)CFArrayGetValueAtIndex(values[i],j);
        CGFloat x=span->x,width=span->width,xend=x+width;
        if((x<xmin && xend<xmin) || (x>xmax && xend>xmax)){continue;}
        rects[nrects++]=CGRectMake(x,drawRect.origin.y,
         width,drawRect.size.height);
      }
      if(nrects){
        CGContextSetFillColorWithColor(context,(CGColorRef)keys[i]);
        CGContextFillRects(context,rects,nrects);
      }
      free(rects);
    }
    free(keys);
    free(values);
  }
  CGContextSetTextMatrix(context,
   CGAffineTransformMake(1,0,0,-1,0,lineAscent));
  CTLineDraw(ctLine,context);
  CFIndex nst=CFDictionaryGetCount(stMap);
  if(nst){// draw strikethrough lines as needed
    const void** keys=malloc(nst*sizeof(CGColorRef));
    const void** values=malloc(nst*sizeof(CFArrayRef));
    CFDictionaryGetKeysAndValues(stMap,keys,values);
    CGFloat ymin=CGRectGetMinY(drawRect),ymax=CGRectGetMaxY(drawRect);
    CFIndex i;
    for (i=0;i<nst;i++){
      CFIndex nvalues=CFArrayGetCount(values[i]),j;
      BOOL first=YES;
      for (j=0;j<nvalues;j++){
        hspan_t* span=(hspan_t*)CFArrayGetValueAtIndex(values[i],j);
        CGFloat x=span->x,xend=x+span->width,y=span->y;
        if((x<xmin && xend<xmin) || (x>xmax && xend>xmax)
         || y<ymin || y>ymax){continue;}
        if(first){
          CGContextSetStrokeColorWithColor(context,(CGColorRef)keys[i]);
          first=NO;
        }
        CGContextMoveToPoint(context,x,y);
        CGContextAddLineToPoint(context,xend,y);
        CGContextStrokePath(context);
      }
    }
    free(keys);
    free(values);
  }
}
-(void)dealloc {
  CGColorRelease(bgColor);
  if(ctLine){CFRelease(ctLine);}
  CFRelease(bgMap);
  CFRelease(stMap);
  [super dealloc];
}
@end