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tomo-old/shatter/shatter.go

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package shatter
import "image"
// Shatter takes in a bounding rectangle, and several rectangles to be
// subtracted from it. It returns a slice of rectangles that tile together to
// make up the difference between them. This is intended to be used for figuring
// out which areas of a container element's background are covered by other
// elements so it doesn't waste CPU cycles drawing to those areas.
func Shatter (
glass image.Rectangle,
rocks ...image.Rectangle,
) (
tiles []image.Rectangle,
) {
// in this function, the metaphor of throwing several rocks at a sheet
// of glass is used to illustrate the concept.
tiles = []image.Rectangle { glass }
for _, rock := range rocks {
// check each tile to see if the rock has collided with it
tileLen := len(tiles)
for tileIndex := 0; tileIndex < tileLen; tileIndex ++ {
tile := tiles[tileIndex]
if !rock.Overlaps(tile) { continue }
newTiles, n := shatterOnce(tile, rock)
if n > 0 {
// the tile was shattered into one or more sub
// tiles
tiles[tileIndex] = newTiles[0]
tiles = append(tiles, newTiles[1:n]...)
} else {
// the tile was entirely obscured by the rock
// and must be wholly removed
tiles = remove(tiles, tileIndex)
tileIndex --
tileLen --
}
}
}
return
}
func shatterOnce (glass, rock image.Rectangle) (tiles [4]image.Rectangle, n int) {
rock = rock.Intersect(glass)
// |'''''''''''|
// | |
// |###|'''| |
// |###|___| |
// | |
// |___________|
if rock.Min.X > glass.Min.X { tiles[n] = image.Rect (
glass.Min.X, rock.Min.Y,
rock.Min.X, rock.Max.Y,
); n ++ }
// |'''''''''''|
// | |
// | |'''|###|
// | |___|###|
// | |
// |___________|
if rock.Max.X < glass.Max.X { tiles[n] = image.Rect (
rock.Max.X, rock.Min.Y,
glass.Max.X, rock.Max.Y,
); n ++ }
// |###########|
// |###########|
// | |'''| |
// | |___| |
// | |
// |___________|
if rock.Min.Y > glass.Min.Y { tiles[n] = image.Rect (
glass.Min.X, glass.Min.Y,
glass.Max.X, rock.Min.Y,
); n ++ }
// |'''''''''''|
// | |
// | |'''| |
// | |___| |
// |###########|
// |###########|
if rock.Max.Y < glass.Max.Y { tiles[n] = image.Rect (
glass.Min.X, rock.Max.Y,
glass.Max.X, glass.Max.Y,
); n ++ }
return
}
func remove[ELEMENT any] (slice []ELEMENT, s int) []ELEMENT {
return append(slice[:s], slice[s + 1:]...)
}