Terminal-based user interface toolkit
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package cview
import (
"sync"
"github.com/gdamore/tcell"
)
// The size of the event/update/redraw channels.
const queueSize = 100
// 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 {
sync.RWMutex
// 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 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
// 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
// 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
}
// NewApplication creates and returns a new application.
func NewApplication() *Application {
return &Application{
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) *Application {
a.inputCapture = capture
return a
}
// 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 {
return a.inputCapture
}
// 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) *Application {
if screen == nil {
return a // Invalid input. Do nothing.
}
a.Lock()
if a.screen == nil {
// Run() has not been called yet.
a.screen = screen
a.Unlock()
return a
}
// Run() is already in progress. Exchange screen.
oldScreen := a.screen
a.Unlock()
oldScreen.Fini()
a.screenReplacement <- screen
return a
}
// Run starts the application and thus the event loop. This function returns
// when Stop() was called.
func (a *Application) Run() error {
var err error
a.Lock()
// Make a screen if there is none yet.
if a.screen == nil {
a.screen, err = tcell.NewScreen()
if err != nil {
a.Unlock()
return err
}
if err = a.screen.Init(); err != nil {
a.Unlock()
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 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
}
// Wait for next event and queue it.
event := screen.PollEvent()
if event != nil {
// Regular event. Queue.
a.QueueEvent(event)
continue
}
// A screen was finalized (event is nil). Wait for a new scren.
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)
}
a.draw()
}
}()
// Start event loop.
EventLoop:
for {
select {
case event := <-a.events:
if event == nil {
break EventLoop
}
switch event := event.(type) {
case *tcell.EventKey:
a.RLock()
p := a.focus
inputCapture := a.inputCapture
a.RUnlock()
// Intercept keys.
if inputCapture != nil {
event = inputCapture(event)
if event == nil {
a.draw()
continue // Don't forward event.
}
}
// Ctrl-C closes the application.
if event.Key() == tcell.KeyCtrlC {
a.Stop()
}
// 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:
a.RLock()
screen := a.screen
a.RUnlock()
if screen == nil {
continue
}
screen.Clear()
a.draw()
}
// If we have updates, now is the time to execute them.
case updater := <-a.updates:
updater()
}
}
// Wait for the event loop to finish.
wg.Wait()
a.screen = nil
return nil
}
// 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.RLock()
screen := a.screen
a.RUnlock()
if screen == nil {
return false // Screen has not yet been initialized.
}
// Enter suspended mode.
screen.Fini()
// Wait for "f" to return.
f()
// Make a new screen.
var err error
screen, err = tcell.NewScreen()
if err != nil {
panic(err)
}
a.screenReplacement <- screen
// One key event will get lost, see https://github.com/gdamore/tcell/issues/194
// Continue application loop.
return true
}
// Draw refreshes the screen (during the next update cycle). It calls the Draw()
// function of the application's root primitive and then syncs the screen
// buffer.
func (a *Application) Draw() *Application {
a.QueueUpdate(func() {
a.draw()
})
return a
}
// ForceDraw refreshes the screen immediately. Use this function with caution as
// it may lead to race conditions with updates to primitives in other
// goroutines. It is always preferrable to use Draw() instead. Never call this
// function from a goroutine.
//
// It is safe to call this function during queued updates and direct event
// handling.
func (a *Application) ForceDraw() *Application {
return a.draw()
}
// draw actually does what Draw() promises to do.
func (a *Application) draw() *Application {
a.Lock()
defer a.Unlock()
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 {
return a
}
// Resize if requested.
if fullscreen && root != nil {
width, height := screen.Size()
root.SetRect(0, 0, width, height)
}
// Call before handler if there is one.
if before != nil {
if before(screen) {
screen.Show()
return a
}
}
// Draw all primitives.
root.Draw(screen)
// Call after handler if there is one.
if after != nil {
after(screen)
}
// Sync screen.
screen.Show()
return a
}
// 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) *Application {
a.beforeDraw = handler
return a
}
// GetBeforeDrawFunc returns the callback function installed with
// SetBeforeDrawFunc() or nil if none has been installed.
func (a *Application) GetBeforeDrawFunc() func(screen tcell.Screen) bool {
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)) *Application {
a.afterDraw = handler
return a
}
// GetAfterDrawFunc returns the callback function installed with
// SetAfterDrawFunc() or nil if none has been installed.
func (a *Application) GetAfterDrawFunc() func(screen tcell.Screen) {
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) *Application {
a.Lock()
a.root = root
a.rootFullscreen = fullscreen
if a.screen != nil {
a.screen.Clear()
}
a.Unlock()
a.SetFocus(root)
return a
}
// ResizeToFullScreen resizes the given primitive such that it fills the entire
// screen.
func (a *Application) ResizeToFullScreen(p Primitive) *Application {
a.RLock()
width, height := a.screen.Size()
a.RUnlock()
p.SetRect(0, 0, width, height)
return a
}
// 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) *Application {
a.Lock()
if a.focus != nil {
a.focus.Blur()
}
a.focus = p
if a.screen != nil {
a.screen.HideCursor()
}
a.Unlock()
if p != nil {
p.Focus(func(p Primitive) {
a.SetFocus(p)
})
}
return a
}
// 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
}
// QueueUpdate is used to synchronize access to primitives from non-main
// goroutines. The provided function will be executed as part of the event loop
// and thus will not cause race conditions with other such update functions or
// the Draw() function.
//
// 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()) *Application {
a.updates <- f
return a
}
// QueueUpdateDraw works like QueueUpdate() except it refreshes the screen
// immediately after executing f.
func (a *Application) QueueUpdateDraw(f func()) *Application {
a.QueueUpdate(func() {
f()
a.draw()
})
return a
}
// 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) *Application {
a.events <- event
return a
}