CODEWITHSUNDEEP
sprite-kitskphysicsbody
Andrey Gordeev
Andrey Gordeev

Reputation: 32459

SKPhysicsBody appears too big

I have an SKSpriteNode of an airplane. Here is image (300px x 83px):

An airplane

The image is named as [email protected] in my Xcode project.

Now I'm adding a physics body to the airplane:

CGFloat offsetX = self.size.width * self.anchorPoint.x;
CGFloat offsetY = self.size.height * self.anchorPoint.y;

CGMutablePathRef path = CGPathCreateMutable();

CGPathMoveToPoint(path, NULL, 24 - offsetX, 124 - offsetY);
CGPathAddLineToPoint(path, NULL, 24 - offsetX, 47 - offsetY);
CGPathAddLineToPoint(path, NULL, 339 - offsetX, 1 - offsetY);
CGPathAddLineToPoint(path, NULL, 401 - offsetX, 3 - offsetY);
CGPathAddLineToPoint(path, NULL, 452 - offsetX, 52 - offsetY);
CGPathAddLineToPoint(path, NULL, 411 - offsetX, 78 - offsetY);
CGPathAddLineToPoint(path, NULL, 295 - offsetX, 78 - offsetY);
CGPathAddLineToPoint(path, NULL, 268 - offsetX, 93 - offsetY);
CGPathAddLineToPoint(path, NULL, 95 - offsetX, 78 - offsetY);
CGPathAddLineToPoint(path, NULL, 62 - offsetX, 124 - offsetY);

CGPathCloseSubpath(path);

self.physicsBody = [SKPhysicsBody bodyWithPolygonFromPath:path];

CGPath is generated by SKPhysicsBody Path Generator

To debug the airplane's physics body I've added an SKShapeNode with the same CGPath as for physics body:

SKShapeNode *shape = [[SKShapeNode alloc] init];
shape.path = path;
shape.strokeColor = [SKColor colorWithRed:1.0 green:0 blue:0 alpha:0.5];
[self addChild:shape];

Here is the result:

result

Am I doing something wrong?

PS: Notices an interesting thing. If I specify CGPath as follows:

CGPathMoveToPoint(path, NULL, 24/3.0 - offsetX, 124/3.0 - offsetY);
CGPathAddLineToPoint(path, NULL, 24/3.0 - offsetX, 47/3.0 - offsetY);

the shape fits the airplane well!

Upvotes: 1

Views: 749

Answers (3)

Bogdan
Bogdan

Reputation: 863

I'm guessing that you need to calculate the points, not the pixels. If you have an @1x image, then it will have the same size in points and pixels. For @2x you will have the same number of points, but double number of pixels and so on for @3x...

Upvotes: 0

JKallio
JKallio

Reputation: 903

You must use the original dimensions (320 x 480) or in case of iPhone5+ (320 x 568). @2x/@4x images are only to provide higher resolution images for retina devices. But for backward compatibility reasons all devices still share the same coordinate system.

So your path should be something like:

SKSpriteNode *sprite = [SKSpriteNode spriteNodeWithImageNamed:@"jPfsF.png"];

CGFloat offsetX = sprite.frame.size.width * sprite.anchorPoint.x;
CGFloat offsetY = sprite.frame.size.height * sprite.anchorPoint.y;

CGMutablePathRef path = CGPathCreateMutable();

CGPathMoveToPoint(path, NULL, 18 - offsetX, 41 - offsetY);
CGPathAddLineToPoint(path, NULL, 31 - offsetX, 25 - offsetY);
CGPathAddLineToPoint(path, NULL, 91 - offsetX, 31 - offsetY);
CGPathAddLineToPoint(path, NULL, 95 - offsetX, 24 - offsetY);
CGPathAddLineToPoint(path, NULL, 136 - offsetX, 26 - offsetY);
CGPathAddLineToPoint(path, NULL, 148 - offsetX, 18 - offsetY);
CGPathAddLineToPoint(path, NULL, 133 - offsetX, 2 - offsetY);
CGPathAddLineToPoint(path, NULL, 75 - offsetX, 1 - offsetY);
CGPathAddLineToPoint(path, NULL, 9 - offsetX, 16 - offsetY);
CGPathAddLineToPoint(path, NULL, 11 - offsetX, 40 - offsetY);

CGPathCloseSubpath(path);

sprite.physicsBody = [SKPhysicsBody bodyWithPolygonFromPath:path];

Upvotes: 0

RichS
RichS

Reputation: 3147

This may not be relevant, but, your defined shape is concave. The docs say it must be convex. If you recreate your path with a convex shape, does that help?

enter image description here

Examples: Convex and Concave polygons

Upvotes: 1

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