Added shatter algorithm to canvas

canvas/shatter.go

@@ -0,0 +1,96 @@
+package canvas
+
+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 box's background are covered by other boxes 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:]...)
+}

event/event.go

@@ -61,5 +61,7 @@ type FuncBroadcaster struct {
 
 // Broadcast calls all connected listener funcs.
 func (broadcaster *FuncBroadcaster) Broadcast () {
-	
+	for _, listener := range broadcaster.Listeners() {
+		listener()
+	}
 }

object.go

@@ -98,12 +98,17 @@ type Align int; const (
 	AlignEven               // similar to justified text
 )
 
+// Object is any obscreen object. Each object must be linked to a box, even if
+// it is that box.
 type Object interface {
 	Box () Box
 }
 
+// Box is a basic styled box.
 type Box interface {
 	Object
+
+	Window         () Window
 	Bounds         () image.Rectangle
 	InnerBounds    () image.Rectangle
 	SetBounds      (image.Rectangle)
@@ -118,8 +123,8 @@ type Box interface {
 	SetFocusable (bool)
 	
 	Focused       () bool
-	Modifiers     (func ()) input.Modifiers
-	MousePosition (func ()) image.Point
+	Modifiers     () input.Modifiers
+	MousePosition () image.Point
 
 	OnFocusEnter  (func ()) event.Cookie
 	OnFocusLeave  (func ()) event.Cookie
@@ -134,28 +139,38 @@ type Box interface {
 	OnScroll      (func (deltaX, deltaY float64)) event.Cookie
 	OnKeyDown     (func (key input.Key, numberPad bool)) event.Cookie
 	OnKeyUp       (func (key input.Key, numberPad bool)) event.Cookie
-
-	ContentBounds         () image.Rectangle
-	ScrollTo              (image.Point)
-	OnContentBoundsChange (func ()) event.Cookie
-}
-
-type TextBox interface {
-	Box
-	SetTextColor (color.Color)
-	SetFace      (font.Face)
-	SetHAlign    (Align)
-	SetVAlign    (Align)
 }
 
+// CanvasBox is a box that can be drawn to.
 type CanvasBox interface {
 	Box
 	SetDrawer  (canvas.Drawer)
 	Invalidate ()
 }
 
-type ContainerBox interface {
+// ContentBox is an abstract box that has some kind of content. Its only purpose
+// is to be embedded into TextBox and ContainerBox.
+type ContentBox interface {
 	Box
+	SetOverflow           (horizontal, vertical bool)
+	ContentBounds         () image.Rectangle
+	ScrollTo              (image.Point)
+	OnContentBoundsChange (func ()) event.Cookie
+}
+
+// TextBox is a box that contains text content.
+type TextBox interface {
+	ContentBox
+	SetTextColor (color.Color)
+	SetFace      (font.Face)
+	SetHAlign    (Align)
+	SetVAlign    (Align)
+}
+
+// ContentBox is a box that can contain child objects. It arranges them
+// according to a layout rule.
+type ContainerBox interface {
+	ContentBox
 	SetGap    (Gap)
 	Add       (Object)
 	Delete    (Object)
@@ -166,6 +181,12 @@ type ContainerBox interface {
 	SetLayout (Layout)
 }
 
+// Layout can be given to a ContainerBox to arrange child objects.
+type Layout interface {
+	Arrange (image.Rectangle, Gap, []Box)
+}
+
+// Window is an operating system window. It can contain one object.
 type Window interface {
 	SetRoot  (Object)
 	SetTitle (string)
@@ -181,11 +202,8 @@ type Window interface {
 	OnClose  (func ()) event.Cookie
 }
 
+// MainWindow is a top-level operating system window.
 type MainWindow interface {
 	Window
 	NewChild (image.Rectangle) (Window, error)
 }
-
-type Layout interface {
-	Arrange (image.Rectangle, Gap, []Box)
-}