EFC - 8 months ago 101

iOS Question

I have an arbitrary

`CGPath`

`CGPathGetPathBoundingBox`

`BOOL moved = NO; // the first coord should be a move, the rest add lines`

CGPoint total = CGPointZero;

for (NSDictionary *coord in [polygon objectForKey:@"coordinates"]) {

CGPoint point = CGPointMake([(NSNumber *)[coord objectForKey:@"x"] floatValue],

[(NSNumber *)[coord objectForKey:@"y"] floatValue]);

if (moved) {

CGContextAddLineToPoint(context, point.x, point.y);

// calculate totals of x and y to help find the center later

// skip the first "move" point since it is repeated at the end in this data

total.x = total.x + point.x;

total.y = total.y + point.y;

} else {

CGContextMoveToPoint(context, point.x, point.y);

moved = YES; // we only move once, then we add lines

}

}

// the center is the average of the total points

CGPoint center = CGPointMake(total.x / ([[polygon objectForKey:@"coordinates"] count]-1), total.y / ([[polygon objectForKey:@"coordinates"] count]-1));

If you have a better idea, please share!

Answer

The technique works, but the code you put in the question doesn't. AFAICS, that only works for the few situations where you are doing straight-line polygons ONLY, *and* you have a list of points, *and* you haven't made the CGPath object yet.

I needed to do it for arbitrary CGPath objects. Using Adam's (other Adam) suggestion, and Apple's CGPathApply, I came up with this, which works very well:

```
{
float dataArray[3] = { 0, 0, 0 };
CGPathApply( (CGPathRef) YOUR_PATH, dataArray, pathApplierSumCoordinatesOfAllPoints);
float averageX = dataArray[0] / dataArray[2];
float averageY = dataArray[1] / dataArray[2];
CGPoint centerOfPath = CGPointMake(averageX, averageY);
}
static void pathApplierSumCoordinatesOfAllPoints(void* info, const CGPathElement* element)
{
float* dataArray = (float*) info;
float xTotal = dataArray[0];
float yTotal = dataArray[1];
float numPoints = dataArray[2];
switch (element->type)
{
case kCGPathElementMoveToPoint:
{
/** for a move to, add the single target point only */
CGPoint p = element->points[0];
xTotal += p.x;
yTotal += p.y;
numPoints += 1.0;
}
break;
case kCGPathElementAddLineToPoint:
{
/** for a line to, add the single target point only */
CGPoint p = element->points[0];
xTotal += p.x;
yTotal += p.y;
numPoints += 1.0;
}
break;
case kCGPathElementAddQuadCurveToPoint:
for( int i=0; i<2; i++ ) // note: quad has TWO not THREE
{
/** for a curve, we add all ppints, including the control poitns */
CGPoint p = element->points[i];
xTotal += p.x;
yTotal += p.y;
numPoints += 1.0;
}
break;
case kCGPathElementAddCurveToPoint:
for( int i=0; i<3; i++ ) // note: cubic has THREE not TWO
{
/** for a curve, we add all ppints, including the control poitns */
CGPoint p = element->points[i];
xTotal += p.x;
yTotal += p.y;
numPoints += 1.0;
}
break;
case kCGPathElementCloseSubpath:
/** for a close path, do nothing */
break;
}
//NSLog(@"new x=%2.2f, new y=%2.2f, new num=%2.2f", xTotal, yTotal, numPoints);
dataArray[0] = xTotal;
dataArray[1] = yTotal;
dataArray[2] = numPoints;
}
```