SpriteKit：计算两个纹理蒙版之间的距离

Question

I have two irregular shapes in SpriteKit, and I want to calculate the vertical distance from the base of a space ship and the (irregular) terrain right below.

Is there a way to do it ? Thanks !

Answer 1

Place an SKPhysicsBody that is in a shape of a line at the center of your ship with a width of 1 and the height of your scene, then in the didBeginContact method, grab the 2 contact points. You now know 2 points, just use the distance formula (in this case it is just y2-y1) and you have your answer

Answer 2

I found a different way to solve my problem, but I think that KnightOfDragon's one is conceptually better (although I did not manage to make it work).

The terrain's texture is essentially a bitmap with opaque and transparent pixels. So I decided to parse these pixels, storing the highest opaque pixel for each column, building a "radar altitude map". So I just have to calculate the difference between the bottom of the ship and the altitude of the column right beneath its center:

CFDataRef imageData = CGDataProviderCopyData(CGImageGetDataProvider(terrain.texture.CGImage));
const UInt32 *pixels = (const UInt32*)CFDataGetBytePtr(imageData);

NSMutableArray *radar = [NSMutableArray new];
for (long col = 0; col < terrain.size.width; col++)
    [radar addObject:@(0)];

for (long ind = 0; ind < (terrain.size.height * terrain.size.width); ind++)
{
    if (pixels[ind] & 0xff000000) // non-transparent pixel
    {
        long line = ind/terrain.size.width;
        long col = ind - (line*terrain.size.width);
        if ([radar[col]integerValue] <terrain.size.height-line) radar[col] = @(terrain.size.height-line);
    }
}

This solution could be optimized, of course. It's just the basic idea.

I've added an image to show the original texture, its representation as opaque/transparent pixels, and a test by putting little white nodes to check where the "surface" was.