Split the functionality of tomo.go into multiple files

element.go

@@ -0,0 +1,100 @@
+package tomo
+
+// ParentHooks is a struct that contains callbacks that let child elements send
+// information to their parent element without the child element knowing
+// anything about the parent element or containing any reference to it. When a
+// parent element adopts a child element, it must set these callbacks.
+type ParentHooks struct {
+	// Draw is called when a part of the child element's surface is updated.
+	// The updated region will be passed to the callback as a sub-image.
+	Draw func (region Canvas)
+
+	// MinimumSizeChange is called when the child element's minimum width
+	// and/or height changes. When this function is called, the element will
+	// have already been resized and there is no need to send it a resize
+	// event.
+	MinimumSizeChange func (width, height int)
+
+	// SelectabilityChange is called when the chid element becomes
+	// selectable or non-selectable.
+	SelectabilityChange func (selectable bool)
+
+	// SelectionRequest is called when the child element element wants
+	// itself to be selected. If the parent element chooses to grant the
+	// request, it must send the child element a selection event and return
+	// true.
+	SelectionRequest func () (granted bool)
+}
+
+// RunDraw runs the Draw hook if it is not nil. If it is nil, it does nothing.
+func (hooks ParentHooks) RunDraw (region Canvas) {
+	if hooks.Draw != nil {
+		hooks.Draw(region)
+	}
+}
+
+// RunMinimumSizeChange runs the MinimumSizeChange hook if it is not nil. If it
+// is nil, it does nothing.
+func (hooks ParentHooks) RunMinimumSizeChange (width, height int) {
+	if hooks.MinimumSizeChange != nil {
+		hooks.MinimumSizeChange(width, height)
+	}
+}
+
+// RunSelectionRequest runs the SelectionRequest hook if it is not nil. If it is
+// nil, it does nothing.
+func (hooks ParentHooks) RunSelectionRequest () (granted bool) {
+	if hooks.SelectionRequest != nil {
+		granted = hooks.SelectionRequest()
+	}
+	return
+}
+
+// RunSelectabilityChange runs the SelectionRequest hook if it is not nil. If it
+// is nil, it does nothing.
+func (hooks ParentHooks) RunSelectabilityChange (selectable bool) {
+	if hooks.SelectabilityChange != nil {
+		hooks.SelectabilityChange(selectable)
+	}
+}
+
+// Element represents a basic on-screen object.
+type Element interface {
+	// Element must implement the Canvas interface. Elements should start
+	// out with a completely blank buffer, and only allocate memory and draw
+	// on it for the first time when sent an EventResize event.
+	Canvas
+
+	// Handle handles an event, propagating it to children if necessary.
+	Handle (event Event)
+
+	// Selectable returns whether this element can be selected. If this
+	// element contains other selectable elements, it must return true.
+	Selectable () (selectable bool)
+
+	// Selected returns whether or not this element is currently selected.
+	// This will always return false if it is not selectable.
+	Selected () (selected bool)
+
+	// If this element contains other elements, and one is selected, this
+	// method will advance the selection in the specified direction. If
+	// the element contains selectable elements but none of them are
+	// selected, it will select the first selectable element. If there are
+	// no more children to be selected in the specified direction, the
+	// element will return false. If the selection could be advanced, it
+	// will return true. If the element contains no selectable child
+	// elements, it will  always return false.
+	AdvanceSelection (direction int) (ok bool)
+
+	// SetParentHooks gives the element callbacks that let it send
+	// information to its parent element without it knowing anything about
+	// the parent element or containing any reference to it. When a parent
+	// element adopts a child element, it must set these callbacks.
+	SetParentHooks (callbacks ParentHooks)
+
+	// MinimumSize specifies the minimum amount of pixels this element's
+	// width and height may be set to. If the element is given a resize
+	// event with dimensions smaller than this, it will use its minimum
+	// instead of the offending dimension(s).
+	MinimumSize () (width, height int)
+}