Terminal-based user interface toolkit
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package cview
import (
"fmt"
"sync"
"time"
"github.com/gdamore/tcell/v2"
)
const (
// The size of the event/update/redraw channels.
queueSize = 100
// The minimum duration between resize event callbacks.
resizeEventThrottle = 50 * time.Millisecond
)
// Application represents the top node of an application.
//
// It is not strictly required to use this class as none of the other classes
// depend on it. However, it provides useful tools to set up an application and
// plays nicely with all widgets.
//
// The following command displays a primitive p on the screen until Ctrl-C is
// pressed:
//
// if err := cview.NewApplication().SetRoot(p, true).Run(); err != nil {
// panic(err)
// }
type Application struct {
// The application's screen. Apart from Run(), this variable should never be
// set directly. Always use the screenReplacement channel after calling
// Fini(), to set a new screen (or nil to stop the application).
screen tcell.Screen
// The size of the application's screen.
width, height int
// The primitive which currently has the keyboard focus.
focus Primitive
// The root primitive to be seen on the screen.
root Primitive
// Whether or not the application resizes the root primitive.
rootFullscreen bool
// Whether or not to enable bracketed paste mode.
enableBracketedPaste bool
// Whether or not to enable mouse events.
enableMouse bool
// An optional capture function which receives a key event and returns the
// event to be forwarded to the default input handler (nil if nothing should
// be forwarded).
inputCapture func(event *tcell.EventKey) *tcell.EventKey
// Time a resize event was last processed.
lastResize time.Time
// Timer limiting how quickly resize events are processed.
throttleResize *time.Timer
// An optional callback function which is invoked when the application's
// window is initialized, and when the application's window size changes.
// After invoking this callback the screen is cleared and the application
// is drawn.
afterResize func(width int, height int)
// An optional callback function which is invoked before the application's
// focus changes.
beforeFocus func(p Primitive) bool
// An optional callback function which is invoked after the application's
// focus changes.
afterFocus func(p Primitive)
// An optional callback function which is invoked just before the root
// primitive is drawn.
beforeDraw func(screen tcell.Screen) bool
// An optional callback function which is invoked after the root primitive
// was drawn.
afterDraw func(screen tcell.Screen)
// Used to send screen events from separate goroutine to main event loop
events chan tcell.Event
// Functions queued from goroutines, used to serialize updates to primitives.
updates chan func()
// An object that the screen variable will be set to after Fini() was called.
// Use this channel to set a new screen object for the application
// (screen.Init() and draw() will be called implicitly). A value of nil will
// stop the application.
screenReplacement chan tcell.Screen
// An optional capture function which receives a mouse event and returns the
// event to be forwarded to the default mouse handler (nil if nothing should
// be forwarded).
mouseCapture func(event *tcell.EventMouse, action MouseAction) (*tcell.EventMouse, MouseAction)
// doubleClickInterval specifies the maximum time between clicks to register a
// double click rather than a single click.
doubleClickInterval time.Duration
mouseCapturingPrimitive Primitive // A Primitive returned by a MouseHandler which will capture future mouse events.
lastMouseX, lastMouseY int // The last position of the mouse.
mouseDownX, mouseDownY int // The position of the mouse when its button was last pressed.
lastMouseClick time.Time // The time when a mouse button was last clicked.
lastMouseButtons tcell.ButtonMask // The last mouse button state.
sync.RWMutex
}
// NewApplication creates and returns a new application.
func NewApplication() *Application {
return &Application{
enableBracketedPaste: true,
events: make(chan tcell.Event, queueSize),
updates: make(chan func(), queueSize),
screenReplacement: make(chan tcell.Screen, 1),
}
}
// SetInputCapture sets a function which captures all key events before they are
// forwarded to the key event handler of the primitive which currently has
// focus. This function can then choose to forward that key event (or a
// different one) by returning it or stop the key event processing by returning
// nil.
//
// Note that this also affects the default event handling of the application
// itself: Such a handler can intercept the Ctrl-C event which closes the
// application.
func (a *Application) SetInputCapture(capture func(event *tcell.EventKey) *tcell.EventKey) {
a.Lock()
defer a.Unlock()
a.inputCapture = capture
}
// GetInputCapture returns the function installed with SetInputCapture() or nil
// if no such function has been installed.
func (a *Application) GetInputCapture() func(event *tcell.EventKey) *tcell.EventKey {
a.RLock()
defer a.RUnlock()
return a.inputCapture
}
// SetMouseCapture sets a function which captures mouse events (consisting of
// the original tcell mouse event and the semantic mouse action) before they are
// forwarded to the appropriate mouse event handler. This function can then
// choose to forward that event (or a different one) by returning it or stop
// the event processing by returning a nil mouse event.
func (a *Application) SetMouseCapture(capture func(event *tcell.EventMouse, action MouseAction) (*tcell.EventMouse, MouseAction)) {
a.mouseCapture = capture
}
// GetMouseCapture returns the function installed with SetMouseCapture() or nil
// if no such function has been installed.
func (a *Application) GetMouseCapture() func(event *tcell.EventMouse, action MouseAction) (*tcell.EventMouse, MouseAction) {
return a.mouseCapture
}
// SetDoubleClickInterval sets the maximum time between clicks to register a
// double click rather than a single click. A standard duration is provided as
// StandardDoubleClick. No interval is set by default, disabling double clicks.
func (a *Application) SetDoubleClickInterval(interval time.Duration) {
a.doubleClickInterval = interval
}
// SetScreen allows you to provide your own tcell.Screen object. For most
// applications, this is not needed and you should be familiar with
// tcell.Screen when using this function.
//
// This function is typically called before the first call to Run(). Init() need
// not be called on the screen.
func (a *Application) SetScreen(screen tcell.Screen) {
if screen == nil {
return // Invalid input. Do nothing.
}
a.Lock()
if a.screen == nil {
// Run() has not been called yet.
a.screen = screen
a.Unlock()
return
}
// Run() is already in progress. Exchange screen.
oldScreen := a.screen
a.Unlock()
oldScreen.Fini()
a.screenReplacement <- screen
}
// GetScreen returns the current tcell.Screen of the application. Lock the
// application when manipulating the screen to prevent race conditions. This
// value is only available after calling Init or Run.
func (a *Application) GetScreen() tcell.Screen {
a.RLock()
defer a.RUnlock()
return a.screen
}
// GetScreenSize returns the size of the application's screen. These values are
// only available after calling Init or Run.
func (a *Application) GetScreenSize() (width, height int) {
a.RLock()
defer a.RUnlock()
return a.width, a.height
}
// Init initializes the application screen. Calling Init before running is not
// required. Its primary use is to populate screen dimensions before running an
// application.
func (a *Application) Init() error {
a.Lock()
defer a.Unlock()
return a.init()
}
func (a *Application) init() error {
if a.screen != nil {
return nil
}
var err error
a.screen, err = tcell.NewScreen()
if err != nil {
a.Unlock()
return err
}
if err = a.screen.Init(); err != nil {
a.Unlock()
return err
}
a.width, a.height = a.screen.Size()
if a.enableBracketedPaste {
a.screen.EnablePaste()
}
if a.enableMouse {
a.screen.EnableMouse()
}
return nil
}
// EnableBracketedPaste enables bracketed paste mode, which is enabled by default.
func (a *Application) EnableBracketedPaste(enable bool) {
a.Lock()
defer a.Unlock()
if enable != a.enableBracketedPaste && a.screen != nil {
if enable {
a.screen.EnablePaste()
} else {
a.screen.DisablePaste()
}
}
a.enableBracketedPaste = enable
}
// EnableMouse enables mouse events.
func (a *Application) EnableMouse(enable bool) {
a.Lock()
defer a.Unlock()
if enable != a.enableMouse && a.screen != nil {
if enable {
a.screen.EnableMouse()
} else {
a.screen.DisableMouse()
}
}
a.enableMouse = enable
}
// Run starts the application and thus the event loop. This function returns
// when Stop() was called.
func (a *Application) Run() error {
a.Lock()
// Initialize screen
err := a.init()
if err != nil {
return err
}
// We catch panics to clean up because they mess up the terminal.
defer func() {
if p := recover(); p != nil {
if a.screen != nil {
a.screen.Fini()
}
panic(p)
}
}()
// Draw the screen for the first time.
a.Unlock()
a.draw()
// Separate loop to wait for screen replacement events.
var wg sync.WaitGroup
wg.Add(1)
go func() {
defer wg.Done()
for {
a.RLock()
screen := a.screen
a.RUnlock()
if screen == nil {
// We have no screen. Let's stop.
a.QueueEvent(nil)
break
}
// A screen was finalized (event is nil). Wait for a new screen.
screen = <-a.screenReplacement
if screen == nil {
// No new screen. We're done.
a.QueueEvent(nil)
return
}
// We have a new screen. Keep going.
a.Lock()
a.screen = screen
a.Unlock()
// Initialize and draw this screen.
if err := screen.Init(); err != nil {
panic(err)
}
if a.enableBracketedPaste {
screen.EnablePaste()
}
if a.enableMouse {
screen.EnableMouse()
}
a.draw()
}
}()
handle := func(event interface{}) {
a.RLock()
p := a.focus
inputCapture := a.inputCapture
screen := a.screen
a.RUnlock()
switch event := event.(type) {
case *tcell.EventKey:
// Intercept keys.
if inputCapture != nil {
event = inputCapture(event)
if event == nil {
a.draw()
return // Don't forward event.
}
}
// Ctrl-C closes the application.
if event.Key() == tcell.KeyCtrlC {
a.Stop()
return
}
// Pass other key events to the currently focused primitive.
if p != nil {
if handler := p.InputHandler(); handler != nil {
handler(event, func(p Primitive) {
a.SetFocus(p)
})
a.draw()
}
}
case *tcell.EventResize:
// Throttle resize events.
if time.Since(a.lastResize) < resizeEventThrottle {
// Stop timer
if a.throttleResize != nil && !a.throttleResize.Stop() {
select {
case <-a.throttleResize.C:
default:
}
}
event := event // Capture
// Start timer
a.throttleResize = time.AfterFunc(resizeEventThrottle, func() {
a.events <- event
})
return
}
a.lastResize = time.Now()
if screen == nil {
return
}
screen.Clear()
a.width, a.height = event.Size()
// Call afterResize handler if there is one.
if a.afterResize != nil {
a.afterResize(a.width, a.height)
}
a.draw()
case *tcell.EventMouse:
consumed, isMouseDownAction := a.fireMouseActions(event)
if consumed {
a.draw()
}
a.lastMouseButtons = event.Buttons()
if isMouseDownAction {
a.mouseDownX, a.mouseDownY = event.Position()
}
}
}
semaphore := &sync.Mutex{}
go func() {
for update := range a.updates {
semaphore.Lock()
update()
semaphore.Unlock()
}
}()
// Start screen event loop.
for {
a.Lock()
screen := a.screen
a.Unlock()
if screen == nil {
break
}
// Wait for next event.
event := screen.PollEvent()
if event == nil {
break
}
semaphore.Lock()
handle(event)
semaphore.Unlock()
}
// Wait for the screen replacement event loop to finish.
wg.Wait()
a.screen = nil
return nil
}
// fireMouseActions analyzes the provided mouse event, derives mouse actions
// from it and then forwards them to the corresponding primitives.
func (a *Application) fireMouseActions(event *tcell.EventMouse) (consumed, isMouseDownAction bool) {
// We want to relay follow-up events to the same target primitive.
var targetPrimitive Primitive
// Helper function to fire a mouse action.
fire := func(action MouseAction) {
switch action {
case MouseLeftDown, MouseMiddleDown, MouseRightDown:
isMouseDownAction = true
}
// Intercept event.
if a.mouseCapture != nil {
event, action = a.mouseCapture(event, action)
if event == nil {
consumed = true
return // Don't forward event.
}
}
// Determine the target primitive.
var primitive, capturingPrimitive Primitive
if a.mouseCapturingPrimitive != nil {
primitive = a.mouseCapturingPrimitive
targetPrimitive = a.mouseCapturingPrimitive
} else if targetPrimitive != nil {
primitive = targetPrimitive
} else {
primitive = a.root
}
if primitive != nil {
if handler := primitive.MouseHandler(); handler != nil {
var wasConsumed bool
wasConsumed, capturingPrimitive = handler(action, event, func(p Primitive) {
a.SetFocus(p)
})
if wasConsumed {
consumed = true
}
}
}
a.mouseCapturingPrimitive = capturingPrimitive
}
x, y := event.Position()
buttons := event.Buttons()
clickMoved := x != a.mouseDownX || y != a.mouseDownY
buttonChanges := buttons ^ a.lastMouseButtons
if x != a.lastMouseX || y != a.lastMouseY {
fire(MouseMove)
a.lastMouseX = x
a.lastMouseY = y
}
for _, buttonEvent := range []struct {
button tcell.ButtonMask
down, up, click, dclick MouseAction
}{
{tcell.ButtonPrimary, MouseLeftDown, MouseLeftUp, MouseLeftClick, MouseLeftDoubleClick},
{tcell.ButtonMiddle, MouseMiddleDown, MouseMiddleUp, MouseMiddleClick, MouseMiddleDoubleClick},
{tcell.ButtonSecondary, MouseRightDown, MouseRightUp, MouseRightClick, MouseRightDoubleClick},
} {
if buttonChanges&buttonEvent.button != 0 {
if buttons&buttonEvent.button != 0 {
fire(buttonEvent.down)
} else {
fire(buttonEvent.up)
if !clickMoved {
if a.doubleClickInterval == 0 || a.lastMouseClick.Add(a.doubleClickInterval).Before(time.Now()) {
fire(buttonEvent.click)
a.lastMouseClick = time.Now()
} else {
fire(buttonEvent.dclick)
a.lastMouseClick = time.Time{} // reset
}
}
}
}
}
for _, wheelEvent := range []struct {
button tcell.ButtonMask
action MouseAction
}{
{tcell.WheelUp, MouseScrollUp},
{tcell.WheelDown, MouseScrollDown},
{tcell.WheelLeft, MouseScrollLeft},
{tcell.WheelRight, MouseScrollRight}} {
if buttons&wheelEvent.button != 0 {
fire(wheelEvent.action)
}
}
return consumed, isMouseDownAction
}
// Stop stops the application, causing Run() to return.
func (a *Application) Stop() {
a.Lock()
defer a.Unlock()
screen := a.screen
if screen == nil {
return
}
a.screen = nil
screen.Fini()
a.screenReplacement <- nil
}
// Suspend temporarily suspends the application by exiting terminal UI mode and
// invoking the provided function "f". When "f" returns, terminal UI mode is
// entered again and the application resumes.
//
// A return value of true indicates that the application was suspended and "f"
// was called. If false is returned, the application was already suspended,
// terminal UI mode was not exited, and "f" was not called.
func (a *Application) Suspend(f func()) bool {
a.Lock()
if a.screen == nil {
a.Unlock()
return false // Screen has not yet been initialized.
}
err := a.screen.Suspend()
a.Unlock()
if err != nil {
panic(err)
}
// Wait for "f" to return.
f()
a.Lock()
err = a.screen.Resume()
a.Unlock()
if err != nil {
panic(err)
}
return true
}
// Draw draws the provided primitives on the screen, or when no primitives are
// provided, draws the application's root primitive (i.e. the entire screen).
//
// When one or more primitives are supplied, the Draw functions of the
// primitives are called. Handlers set via BeforeDrawFunc and AfterDrawFunc are
// not called.
//
// When no primitives are provided, the Draw function of the application's root
// primitive is called. This results in drawing the entire screen. Handlers set
// via BeforeDrawFunc and AfterDrawFunc are also called.
func (a *Application) Draw(p ...Primitive) {
a.QueueUpdate(func() {
if len(p) == 0 {
a.draw()
return
}
a.Lock()
if a.screen != nil {
for _, primitive := range p {
primitive.Draw(a.screen)
}
a.screen.Show()
}
a.Unlock()
})
}
// draw actually does what Draw() promises to do.
func (a *Application) draw() {
a.Lock()
screen := a.screen
root := a.root
fullscreen := a.rootFullscreen
before := a.beforeDraw
after := a.afterDraw
// Maybe we're not ready yet or not anymore.
if screen == nil || root == nil {
a.Unlock()
return
}
// Resize if requested.
if fullscreen {
root.SetRect(0, 0, a.width, a.height)
}
// Call before handler if there is one.
if before != nil {
a.Unlock()
if before(screen) {
screen.Show()
return
}
} else {
a.Unlock()
}
// Draw all primitives.
root.Draw(screen)
// Call after handler if there is one.
if after != nil {
after(screen)
}
// Sync screen.
screen.Show()
}
// SetBeforeDrawFunc installs a callback function which is invoked just before
// the root primitive is drawn during screen updates. If the function returns
// true, drawing will not continue, i.e. the root primitive will not be drawn
// (and an after-draw-handler will not be called).
//
// Note that the screen is not cleared by the application. To clear the screen,
// you may call screen.Clear().
//
// Provide nil to uninstall the callback function.
func (a *Application) SetBeforeDrawFunc(handler func(screen tcell.Screen) bool) {
a.Lock()
defer a.Unlock()
a.beforeDraw = handler
}
// GetBeforeDrawFunc returns the callback function installed with
// SetBeforeDrawFunc() or nil if none has been installed.
func (a *Application) GetBeforeDrawFunc() func(screen tcell.Screen) bool {
a.RLock()
defer a.RUnlock()
return a.beforeDraw
}
// SetAfterDrawFunc installs a callback function which is invoked after the root
// primitive was drawn during screen updates.
//
// Provide nil to uninstall the callback function.
func (a *Application) SetAfterDrawFunc(handler func(screen tcell.Screen)) {
a.Lock()
defer a.Unlock()
a.afterDraw = handler
}
// GetAfterDrawFunc returns the callback function installed with
// SetAfterDrawFunc() or nil if none has been installed.
func (a *Application) GetAfterDrawFunc() func(screen tcell.Screen) {
a.RLock()
defer a.RUnlock()
return a.afterDraw
}
// SetRoot sets the root primitive for this application. If "fullscreen" is set
// to true, the root primitive's position will be changed to fill the screen.
//
// This function must be called at least once or nothing will be displayed when
// the application starts.
//
// It also calls SetFocus() on the primitive.
func (a *Application) SetRoot(root Primitive, fullscreen bool) {
a.Lock()
a.root = root
a.rootFullscreen = fullscreen
if a.screen != nil {
a.screen.Clear()
}
a.Unlock()
a.SetFocus(root)
}
// ResizeToFullScreen resizes the given primitive such that it fills the entire
// screen.
func (a *Application) ResizeToFullScreen(p Primitive) {
a.RLock()
width, height := a.width, a.height
a.RUnlock()
p.SetRect(0, 0, width, height)
}
// SetAfterResizeFunc installs a callback function which is invoked when the
// application's window is initialized, and when the application's window size
// changes. After invoking this callback the screen is cleared and the
// application is drawn.
//
// Provide nil to uninstall the callback function.
func (a *Application) SetAfterResizeFunc(handler func(width int, height int)) {
a.Lock()
defer a.Unlock()
a.afterResize = handler
}
// GetAfterResizeFunc returns the callback function installed with
// SetAfterResizeFunc() or nil if none has been installed.
func (a *Application) GetAfterResizeFunc() func(width int, height int) {
a.RLock()
defer a.RUnlock()
return a.afterResize
}
// SetFocus sets the focus on a new primitive. All key events will be redirected
// to that primitive. Callers must ensure that the primitive will handle key
// events.
//
// Blur() will be called on the previously focused primitive. Focus() will be
// called on the new primitive.
func (a *Application) SetFocus(p Primitive) {
a.Lock()
if a.beforeFocus != nil {
a.Unlock()
ok := a.beforeFocus(p)
if !ok {
return
}
a.Lock()
}
if a.focus != nil {
a.focus.Blur()
}
a.focus = p
if a.screen != nil {
a.screen.HideCursor()
}
if a.afterFocus != nil {
a.Unlock()
a.afterFocus(p)
} else {
a.Unlock()
}
if p != nil {
p.Focus(func(p Primitive) {
a.SetFocus(p)
})
}
}
// GetFocus returns the primitive which has the current focus. If none has it,
// nil is returned.
func (a *Application) GetFocus() Primitive {
a.RLock()
defer a.RUnlock()
return a.focus
}
// SetBeforeFocusFunc installs a callback function which is invoked before the
// application's focus changes. Return false to maintain the current focus.
//
// Provide nil to uninstall the callback function.
func (a *Application) SetBeforeFocusFunc(handler func(p Primitive) bool) {
a.Lock()
defer a.Unlock()
a.beforeFocus = handler
}
// SetAfterFocusFunc installs a callback function which is invoked after the
// application's focus changes.
//
// Provide nil to uninstall the callback function.
func (a *Application) SetAfterFocusFunc(handler func(p Primitive)) {
a.Lock()
defer a.Unlock()
a.afterFocus = handler
}
// QueueUpdate queues a function to be executed as part of the event loop.
//
// Note that Draw() is not implicitly called after the execution of f as that
// may not be desirable. You can call Draw() from f if the screen should be
// refreshed after each update. Alternatively, use QueueUpdateDraw() to follow
// up with an immediate refresh of the screen.
func (a *Application) QueueUpdate(f func()) {
a.updates <- f
}
// QueueUpdateDraw works like QueueUpdate() except, when one or more primitives
// are provided, the primitives are drawn after the provided function returns.
// When no primitives are provided, the entire screen is drawn after the
// provided function returns.
func (a *Application) QueueUpdateDraw(f func(), p ...Primitive) {
a.QueueUpdate(func() {
f()
if len(p) == 0 {
a.draw()
return
}
a.Lock()
if a.screen != nil {
for _, primitive := range p {
primitive.Draw(a.screen)
}
a.screen.Show()
}
a.Unlock()
})
}
// QueueEvent sends an event to the Application event loop.
//
// It is not recommended for event to be nil.
func (a *Application) QueueEvent(event tcell.Event) {
a.events <- event
}
// RingBell sends a bell code to the terminal.
func (a *Application) RingBell() {
a.QueueUpdate(func() {
fmt.Print(string(byte(7)))
})
}