Made interfacial changes that will allow for elements to be clipped

elements/core/core.go

@@ -8,6 +8,7 @@ import "git.tebibyte.media/sashakoshka/tomo/canvas"
 // widgets. It is meant to be embedded directly into a struct.
 type Core struct {
 	canvas canvas.Canvas
+	bounds image.Rectangle
 
 	metrics struct {
 		minimumWidth  int
@@ -37,7 +38,7 @@ func NewCore (
 // overridden.
 func (core *Core) Bounds () (bounds image.Rectangle) {
 	if core.canvas == nil { return }
-	return core.canvas.Bounds()
+	return core.bounds
 }
 
 // MinimumSize fulfils the tomo.Element interface. This should not need to be
@@ -48,8 +49,9 @@ func (core *Core) MinimumSize () (width, height int) {
 
 // DrawTo fulfills the tomo.Element interface. This should not need to be
 // overridden.
-func (core *Core) DrawTo (canvas canvas.Canvas) {
+func (core *Core) DrawTo (canvas canvas.Canvas, bounds image.Rectangle) {
 	core.canvas = canvas
+	core.bounds = bounds
 	if core.drawSizeChange != nil && core.canvas != nil {
 		core.drawSizeChange()
 	}

elements/element.go

@@ -9,13 +9,14 @@ import "git.tebibyte.media/sashakoshka/tomo/config"
 // Element represents a basic on-screen object.
 type Element interface {
 	// Bounds reports the element's bounding box. This must reflect the
-	// bounding box of the last canvas given to the element by DrawTo.
+	// bounding last given to the element by DrawTo.
 	Bounds () (bounds image.Rectangle)
 
-	// DrawTo sets this element's canvas. This should only be called by the
-	// parent element. This is typically a region of the parent element's
-	// canvas.
-	DrawTo (canvas canvas.Canvas)
+	// DrawTo gives the element a canvas to draw on, along with a bounding
+	// box to be used for laying out the element. This should only be called
+	// by the parent element. This is typically a region of the parent
+	// element's canvas.
+	DrawTo (canvas canvas.Canvas, bounds image.Rectangle)
 
 	// OnDamage sets a function to be called when an area of the element is
 	// drawn on and should be pushed to the screen.