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tomo-old/element.go
2023-01-31 14:29:35 -05:00

178 lines
6.5 KiB
Go

package tomo
import "image"
// 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
// 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)
// 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)
// OnDamage sets a function to be called when an area of the element is
// drawn on and should be pushed to the screen.
OnDamage (callback func (region Canvas))
// OnMinimumSizeChange sets a function to be called when the element's
// minimum size is changed.
OnMinimumSizeChange (callback func ())
}
// KeynavDirection represents a keyboard navigation direction.
type KeynavDirection int
const (
KeynavDirectionNeutral KeynavDirection = 0
KeynavDirectionBackward KeynavDirection = -1
KeynavDirectionForward KeynavDirection = 1
)
// Canon returns a well-formed direction.
func (direction KeynavDirection) Canon () (canon KeynavDirection) {
if direction > 0 {
return KeynavDirectionForward
} else if direction == 0 {
return KeynavDirectionNeutral
} else {
return KeynavDirectionBackward
}
}
// Focusable represents an element that has keyboard navigation support. This
// includes inputs, buttons, sliders, etc. as well as any elements that have
// children (so keyboard navigation events can be propagated downward).
type Focusable interface {
Element
// Focused returns whether or not this element is currently focused.
Focused () (selected bool)
// Focus focuses this element, if its parent element grants the
// request.
Focus ()
// HandleFocus causes this element to mark itself as focused. If the
// element does not have children, it is disabled, or there are no more
// selectable children in the given direction, it should return false
// and do nothing. Otherwise, it should select itself and any children
// (if applicable) and return true.
HandleFocus (direction KeynavDirection) (accepted bool)
// HandleDeselection causes this element to mark itself and all of its
// children as unfocused.
HandleUnfocus ()
// OnFocusRequest sets a function to be called when this element wants
// its parent element to focus it. Parent elements should return true if
// the request was granted, and false if it was not.
OnFocusRequest (func () (granted bool))
// OnFocusMotionRequest sets a function to be called when this
// element wants its parent element to focus the element behind or in
// front of it, depending on the specified direction. Parent elements
// should return true if the request was granted, and false if it was
// not.
OnFocusMotionRequest (func (direction KeynavDirection) (granted bool))
}
// KeyboardTarget represents an element that can receive keyboard input.
type KeyboardTarget interface {
Element
// HandleKeyDown is called when a key is pressed down or repeated while
// this element has keyboard focus. It is important to note that not
// every key down event is guaranteed to be paired with exactly one key
// up event. This is the reason a list of modifier keys held down at the
// time of the key press is given.
HandleKeyDown (key Key, modifiers Modifiers)
// HandleKeyUp is called when a key is released while this element has
// keyboard focus.
HandleKeyUp (key Key, modifiers Modifiers)
}
// MouseTarget represents an element that can receive mouse events.
type MouseTarget interface {
Element
// Each of these handler methods is passed the position of the mouse
// cursor at the time of the event as x, y.
// HandleMouseDown is called when a mouse button is pressed down on this
// element.
HandleMouseDown (x, y int, button Button)
// HandleMouseUp is called when a mouse button is released that was
// originally pressed down on this element.
HandleMouseUp (x, y int, button Button)
// HandleMouseMove is called when the mouse is moved over this element,
// or the mouse is moving while being held down and originally pressed
// down on this element.
HandleMouseMove (x, y int)
// HandleScroll is called when the mouse is scrolled. The X and Y
// direction of the scroll event are passed as deltaX and deltaY.
HandleMouseScroll (x, y int, deltaX, deltaY float64)
}
// Flexible represents an element who's preferred minimum height can change in
// response to its width.
type Flexible interface {
Element
// FlexibleHeightFor returns what the element's minimum height would be
// if resized to a specified width. This does not actually alter the
// state of the element in any way, but it may perform significant work,
// so it should be called sparingly.
//
// It is reccomended that parent containers check for this interface and
// take this method's value into account in order to support things like
// flow layouts and text wrapping, but it is not absolutely necessary.
// The element's MinimumSize method will still return the absolute
// minimum size that the element may be resized to.
//
// It is important to note that if a parent container checks for
// flexible chilren, it itself will likely need to be flexible.
FlexibleHeightFor (width int) (height int)
// OnFlexibleHeightChange sets a function to be called when the
// parameters affecting this element's flexible height are changed.
OnFlexibleHeightChange (callback func ())
}
// Scrollable represents an element that can be scrolled. It acts as a viewport
// through which its contents can be observed.
type Scrollable interface {
Element
// ScrollContentBounds returns the full content size of the element.
ScrollContentBounds () (bounds image.Rectangle)
// ScrollViewportBounds returns the size and position of the element's
// viewport relative to ScrollBounds.
ScrollViewportBounds () (bounds image.Rectangle)
// ScrollTo scrolls the viewport to the specified point relative to
// ScrollBounds.
ScrollTo (position image.Point)
// ScrollAxes returns the supported axes for scrolling.
ScrollAxes () (horizontal, vertical bool)
// OnScrollBoundsChange sets a function to be called when the element's
// ScrollContentBounds, ScrollViewportBounds, or ScrollAxes are changed.
OnScrollBoundsChange (callback func ())
}