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