314 lines
7.7 KiB
Markdown
314 lines
7.7 KiB
Markdown
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# _Tcell_ Tutorial
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_Tcell_ provides a low-level, portable API for building terminal-based programs.
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A [terminal emulator](https://en.wikipedia.org/wiki/Terminal_emulator)
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(or a real terminal such as a DEC VT-220) is used to interact with such a program.
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_Tcell_'s interface is fairly low-level.
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While it provides a reasonably portable way of dealing with all the usual terminal
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features, it may be easier to utilize a higher level framework.
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A number of such frameworks are listed on the _Tcell_ main [README](README.md).
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This tutorial provides the details of _Tcell_, and is appropriate for developers
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wishing to create their own application frameworks or needing more direct access
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to the terminal capabilities.
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## Resize events
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Applications receive an event of type `EventResize` when they are first initialized and each time the terminal is resized.
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The new size is available as `Size`.
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```go
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switch ev := ev.(type) {
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case *tcell.EventResize:
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w, h := ev.Size()
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logMessage(fmt.Sprintf("Resized to %dx%d", w, h))
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}
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```
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## Key events
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When a key is pressed, applications receive an event of type `EventKey`.
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This event describes the modifier keys pressed (if any) and the pressed key or rune.
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When a rune key is pressed, an event with its `Key` set to `KeyRune` is dispatched.
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When a non-rune key is pressed, it is available as the `Key` of the event.
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```go
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switch ev := ev.(type) {
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case *tcell.EventKey:
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mod, key, ch := ev.Mod(), ev.Key(), ev.Rune()
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logMessage(fmt.Sprintf("EventKey Modifiers: %d Key: %d Rune: %d", mod, key, ch))
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}
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```
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### Key event restrictions
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Terminal-based programs have less visibility into keyboard activity than graphical applications.
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When a key is pressed and held, additional key press events are sent by the terminal emulator.
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The rate of these repeated events depends on the emulator's configuration.
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Key release events are not available.
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It is not possible to distinguish runes typed while holding shift and runes typed using caps lock.
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Capital letters are reported without the Shift modifier.
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## Mouse events
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Applications receive an event of type `EventMouse` when the mouse moves, or a mouse button is pressed or released.
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Mouse events are only delivered if
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`EnableMouse` has been called.
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The mouse buttons being pressed (if any) are available as `Buttons`, and the position of the mouse is available as `Position`.
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```go
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switch ev := ev.(type) {
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case *tcell.EventMouse:
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mod := ev.Modifiers()
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btns := ev.Buttons()
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x, y := ev.Position()
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logMessage(fmt.Sprintf("EventMouse Modifiers: %d Buttons: %d Position: %d,%d", mod, btns, x, y))
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}
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```
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### Mouse buttons
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Identifier | Alias | Description
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-----------|-----------------|-----------
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Button1 | ButtonPrimary | Left button
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Button2 | ButtonSecondary | Right button
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Button3 | ButtonMiddle | Middle button
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Button4 | | Side button (thumb/next)
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Button5 | | Side button (thumb/prev)
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WheelUp | | Scroll wheel up
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WheelDown | | Scroll wheel down
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WheelLeft | | Horizontal wheel left
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WheelRight | | Horizontal wheel right
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## Usage
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To create a _Tcell_ application, first initialize a screen to hold it.
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```go
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s, err := tcell.NewScreen()
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if err != nil {
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log.Fatalf("%+v", err)
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}
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if err := s.Init(); err != nil {
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log.Fatalf("%+v", err)
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}
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// Set default text style
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defStyle := tcell.StyleDefault.Background(tcell.ColorReset).Foreground(tcell.ColorReset)
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s.SetStyle(defStyle)
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// Clear screen
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s.Clear()
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```
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Text may be drawn on the screen using `SetContent`.
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```go
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s.SetContent(0, 0, 'H', nil, defStyle)
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s.SetContent(1, 0, 'i', nil, defStyle)
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s.SetContent(2, 0, '!', nil, defStyle)
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```
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To draw text more easily, define a render function.
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```go
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func drawText(s tcell.Screen, x1, y1, x2, y2 int, style tcell.Style, text string) {
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row := y1
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col := x1
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for _, r := range []rune(text) {
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s.SetContent(col, row, r, nil, style)
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col++
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if col >= x2 {
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row++
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col = x1
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}
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if row > y2 {
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break
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}
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}
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}
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```
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Lastly, define an event loop to handle user input and update application state.
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```go
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quit := func() {
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s.Fini()
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os.Exit(0)
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}
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for {
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// Update screen
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s.Show()
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// Poll event
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ev := s.PollEvent()
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// Process event
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switch ev := ev.(type) {
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case *tcell.EventResize:
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s.Sync()
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case *tcell.EventKey:
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if ev.Key() == tcell.KeyEscape || ev.Key() == tcell.KeyCtrlC {
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quit()
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}
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}
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}
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```
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## Demo application
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The following demonstrates how to initialize a screen, draw text/graphics and handle user input.
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```go
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package main
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import (
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"fmt"
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"log"
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"github.com/gdamore/tcell/v2"
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)
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func drawText(s tcell.Screen, x1, y1, x2, y2 int, style tcell.Style, text string) {
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row := y1
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col := x1
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for _, r := range []rune(text) {
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s.SetContent(col, row, r, nil, style)
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col++
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if col >= x2 {
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row++
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col = x1
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}
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if row > y2 {
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break
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}
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}
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}
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func drawBox(s tcell.Screen, x1, y1, x2, y2 int, style tcell.Style, text string) {
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if y2 < y1 {
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y1, y2 = y2, y1
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}
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if x2 < x1 {
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x1, x2 = x2, x1
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}
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// Fill background
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for row := y1; row <= y2; row++ {
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for col := x1; col <= x2; col++ {
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s.SetContent(col, row, ' ', nil, style)
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}
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}
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// Draw borders
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for col := x1; col <= x2; col++ {
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s.SetContent(col, y1, tcell.RuneHLine, nil, style)
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s.SetContent(col, y2, tcell.RuneHLine, nil, style)
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}
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for row := y1 + 1; row < y2; row++ {
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s.SetContent(x1, row, tcell.RuneVLine, nil, style)
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s.SetContent(x2, row, tcell.RuneVLine, nil, style)
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}
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// Only draw corners if necessary
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if y1 != y2 && x1 != x2 {
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s.SetContent(x1, y1, tcell.RuneULCorner, nil, style)
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s.SetContent(x2, y1, tcell.RuneURCorner, nil, style)
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s.SetContent(x1, y2, tcell.RuneLLCorner, nil, style)
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s.SetContent(x2, y2, tcell.RuneLRCorner, nil, style)
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}
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drawText(s, x1+1, y1+1, x2-1, y2-1, style, text)
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}
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func main() {
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defStyle := tcell.StyleDefault.Background(tcell.ColorReset).Foreground(tcell.ColorReset)
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boxStyle := tcell.StyleDefault.Foreground(tcell.ColorWhite).Background(tcell.ColorPurple)
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// Initialize screen
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s, err := tcell.NewScreen()
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if err != nil {
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log.Fatalf("%+v", err)
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}
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if err := s.Init(); err != nil {
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log.Fatalf("%+v", err)
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}
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s.SetStyle(defStyle)
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s.EnableMouse()
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s.EnablePaste()
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s.Clear()
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// Draw initial boxes
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drawBox(s, 1, 1, 42, 7, boxStyle, "Click and drag to draw a box")
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drawBox(s, 5, 9, 32, 14, boxStyle, "Press C to reset")
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quit := func() {
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// You have to catch panics in a defer, clean up, and
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// re-raise them - otherwise your application can
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// die without leaving any diagnostic trace.
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maybePanic := recover()
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s.Fini()
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if maybePanic != nil {
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panic(maybePanic)
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}
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}
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defer quit()
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// Here's how to get the screen size when you need it.
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// xmax, ymax := s.Size()
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// Here's an example of how to inject a keystroke where it will
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// be picked up by the next PollEvent call. Note that the
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// queue is LIFO, it has a limited length, and PostEvent() can
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// return an error.
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// s.PostEvent(tcell.NewEventKey(tcell.KeyRune, rune('a'), 0))
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// Event loop
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ox, oy := -1, -1
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for {
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// Update screen
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s.Show()
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// Poll event
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ev := s.PollEvent()
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// Process event
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switch ev := ev.(type) {
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case *tcell.EventResize:
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s.Sync()
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case *tcell.EventKey:
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if ev.Key() == tcell.KeyEscape || ev.Key() == tcell.KeyCtrlC {
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return
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} else if ev.Key() == tcell.KeyCtrlL {
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s.Sync()
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} else if ev.Rune() == 'C' || ev.Rune() == 'c' {
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s.Clear()
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}
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case *tcell.EventMouse:
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x, y := ev.Position()
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switch ev.Buttons() {
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case tcell.Button1, tcell.Button2:
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if ox < 0 {
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ox, oy = x, y // record location when click started
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}
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case tcell.ButtonNone:
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if ox >= 0 {
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label := fmt.Sprintf("%d,%d to %d,%d", ox, oy, x, y)
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drawBox(s, ox, oy, x, y, boxStyle, label)
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ox, oy = -1, -1
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}
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}
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}
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}
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}
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```
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