Package com.googlecode.lanterna.screen

Interface Screen

All Superinterfaces:

AutoCloseable, Closeable, InputProvider, Scrollable

All Known Implementing Classes:

AbstractScreen, TerminalScreen, VirtualScreen

public interface Screen
extends InputProvider, Scrollable, Closeable

Screen is a fundamental layer in Lanterna, presenting the terminal as a bitmap-like surface where you can perform smaller in-memory operations to a back-buffer, effectively painting out the terminal as you'd like it, and then call refresh to have the screen automatically apply the changes in the back-buffer to the real terminal. The screen tracks what's visible through a front-buffer, but this is completely managed internally and cannot be expected to know what the terminal looks like if it's being modified externally.

If you want to do more complicated drawing operations, please see the class DefaultScreenWriter which has many utility methods that works on Screens.

Author:

Martin

Nested Class Summary

Nested Classes

Modifier and Type	Interface	Description
static class	Screen.RefreshType	This enum represents the different ways a Screen can refresh the screen, moving the back-buffer data into the front-buffer that is being displayed.

Field Summary

Fields

Modifier and Type	Field	Description
static TextCharacter	DEFAULT_CHARACTER	This is the character Screen implementations should use as a filler is there are areas not set to any particular character.

Method Summary

Modifier and Type	Method	Description
void	clear()	Erases all the characters on the screen, effectively giving you a blank area.
void	close()	Same as calling stopScreen()
TerminalSize	doResizeIfNecessary()	One problem working with Screens is that whenever the terminal is resized, the front and back buffers needs to be adjusted accordingly and the program should have a chance to figure out what to do with this extra space (or less space).
TextCharacter	getBackCharacter(int column, int row)	Reads a character and its associated meta-data from the back-buffer and returns it encapsulated as a ScreenCharacter.
TextCharacter	getBackCharacter(TerminalPosition position)	Reads a character and its associated meta-data from the back-buffer and returns it encapsulated as a ScreenCharacter.
TerminalPosition	getCursorPosition()	A screen implementation typically keeps a location on the screen where the cursor will be placed after drawing and refreshing the buffers, this method returns that location.
TextCharacter	getFrontCharacter(int column, int row)	Reads a character and its associated meta-data from the front-buffer and returns it encapsulated as a ScreenCharacter.
TextCharacter	getFrontCharacter(TerminalPosition position)	Reads a character and its associated meta-data from the front-buffer and returns it encapsulated as a ScreenCharacter.
TabBehaviour	getTabBehaviour()	Gets the behaviour for what to do about tab characters.
TerminalSize	getTerminalSize()	Returns the size of the screen.
TextGraphics	newTextGraphics()	Creates a new TextGraphics objects that is targeting this Screen for writing to.
void	refresh()	This method will take the content from the back-buffer and move it into the front-buffer, making the changes visible to the terminal in the process.
void	refresh(Screen.RefreshType refreshType)	This method will take the content from the back-buffer and move it into the front-buffer, making the changes visible to the terminal in the process.
void	scrollLines(int firstLine, int lastLine, int distance)	Scroll a range of lines of this Screen according to given distance.
void	setCharacter(int column, int row, TextCharacter screenCharacter)	Sets a character in the back-buffer to a specified value with specified colors and modifiers.
void	setCharacter(TerminalPosition position, TextCharacter screenCharacter)	Sets a character in the back-buffer to a specified value with specified colors and modifiers.
void	setCursorPosition(TerminalPosition position)	A screen implementation typically keeps a location on the screen where the cursor will be placed after drawing and refreshing the buffers, this method controls that location.
void	setTabBehaviour(TabBehaviour tabBehaviour)	Sets the behaviour for what to do about tab characters.
void	startScreen()	Before you can use a Screen, you need to start it.
void	stopScreen()	Calling this method will make the underlying terminal leave private mode, effectively going back to whatever state the terminal was in before calling startScreen().

Methods inherited from interface com.googlecode.lanterna.input.InputProvider

pollInput, readInput

Field Detail

DEFAULT_CHARACTER

static final TextCharacter DEFAULT_CHARACTER

This is the character Screen implementations should use as a filler is there are areas not set to any particular character.

Method Detail

startScreen

void startScreen()
          throws IOException

Before you can use a Screen, you need to start it. By starting the screen, Lanterna will make sure the terminal is in private mode (Screen only supports private mode), clears it (so that is can set the front and back buffers to a known value) and places the cursor in the top left corner. After calling startScreen(), you can begin using the other methods on this interface. When you want to exit from the screen and return to what you had before, you can call stopScreen().

Throws:

IOException - if there was an underlying IO error when exiting from private mode

close

void close()
    throws IOException

Same as calling stopScreen()

Specified by:

close in interface AutoCloseable

Specified by:

close in interface Closeable

Throws:

IOException - if there was an underlying IO error when exiting from private mode

stopScreen

void stopScreen()
         throws IOException

Calling this method will make the underlying terminal leave private mode, effectively going back to whatever state the terminal was in before calling startScreen(). Once a screen has been stopped, you can start it again with startScreen() which will restore the screens content to the terminal.

Throws:

IOException - if there was an underlying IO error when exiting from private mode

clear

void clear()

Erases all the characters on the screen, effectively giving you a blank area. The default background color will be used. This is effectively the same as calling

fill(TerminalPosition.TOP_LEFT_CORNER, getSize(), TextColor.ANSI.Default)

.

Please note that calling this method will only affect the back buffer, you need to call refresh to make the change visible.

getCursorPosition

TerminalPosition getCursorPosition()

A screen implementation typically keeps a location on the screen where the cursor will be placed after drawing and refreshing the buffers, this method returns that location. If it returns null, it means that the terminal will attempt to hide the cursor (if supported by the terminal).

Returns:

Position where the cursor will be located after the screen has been refreshed or null if the cursor is not visible

setCursorPosition

void setCursorPosition(TerminalPosition position)

A screen implementation typically keeps a location on the screen where the cursor will be placed after drawing and refreshing the buffers, this method controls that location. If you pass null, it means that the terminal will attempt to hide the cursor (if supported by the terminal).

Parameters:

position - TerminalPosition of the new position where the cursor should be placed after refresh(), or if null, hides the cursor

getTabBehaviour

TabBehaviour getTabBehaviour()

Gets the behaviour for what to do about tab characters. If a tab character is written to the Screen, it would cause issues because we don't know how the terminal emulator would render it and we wouldn't know what state the front-buffer is in. Because of this, we convert tabs to a determined number of spaces depending on different rules that are available.

Returns:

Tab behaviour that is used currently

See Also:

TabBehaviour

setTabBehaviour

void setTabBehaviour(TabBehaviour tabBehaviour)

Sets the behaviour for what to do about tab characters. If a tab character is written to the Screen, it would cause issues because we don't know how the terminal emulator would render it and we wouldn't know what state the front-buffer is in. Because of this, we convert tabs to a determined number of spaces depending on different rules that are available.

Parameters:

tabBehaviour - Tab behaviour to use when converting a \t character to a spaces

See Also:

TabBehaviour

getTerminalSize

TerminalSize getTerminalSize()

Returns the size of the screen. This call is not blocking but should return the size of the screen as it is represented by the buffer at the time this method is called.

Returns:

Size of the screen, in columns and rows

setCharacter

void setCharacter(int column,
                  int row,
                  TextCharacter screenCharacter)

Sets a character in the back-buffer to a specified value with specified colors and modifiers.

Parameters:

column - Column of the character to modify (x coordinate)

row - Row of the character to modify (y coordinate)

screenCharacter - New data to put at the specified position

setCharacter

void setCharacter(TerminalPosition position,
                  TextCharacter screenCharacter)

Sets a character in the back-buffer to a specified value with specified colors and modifiers.

Parameters:

position - Which position in the terminal to modify

screenCharacter - New data to put at the specified position

newTextGraphics

TextGraphics newTextGraphics()

Creates a new TextGraphics objects that is targeting this Screen for writing to. Any operations done on this TextGraphics will be affecting this screen. Remember to call refresh() on the screen to see your changes.

Returns:

New TextGraphic object targeting this Screen

getFrontCharacter

TextCharacter getFrontCharacter(int column,
                                int row)

Reads a character and its associated meta-data from the front-buffer and returns it encapsulated as a ScreenCharacter.

Parameters:

column - Which column to get the character from

row - Which row to get the character from

Returns:

A ScreenCharacter representation of the character in the front-buffer at the specified location

getFrontCharacter

TextCharacter getFrontCharacter(TerminalPosition position)

Reads a character and its associated meta-data from the front-buffer and returns it encapsulated as a ScreenCharacter.

Parameters:

position - What position to read the character from

Returns:

A ScreenCharacter representation of the character in the front-buffer at the specified location

getBackCharacter

TextCharacter getBackCharacter(int column,
                               int row)

Reads a character and its associated meta-data from the back-buffer and returns it encapsulated as a ScreenCharacter.

Parameters:

column - Which column to get the character from

row - Which row to get the character from

Returns:

A ScreenCharacter representation of the character in the back-buffer at the specified location

getBackCharacter

TextCharacter getBackCharacter(TerminalPosition position)

Reads a character and its associated meta-data from the back-buffer and returns it encapsulated as a ScreenCharacter.

Parameters:

position - What position to read the character from

Returns:

A ScreenCharacter representation of the character in the back-buffer at the specified location

refresh

void refresh()
      throws IOException

This method will take the content from the back-buffer and move it into the front-buffer, making the changes visible to the terminal in the process. The graphics workflow with Screen would involve drawing text and text-like graphics on the back buffer and then finally calling refresh(..) to make it visible to the user.

Throws:

IOException - If there was an underlying I/O error

See Also:

Screen.RefreshType

refresh

void refresh(Screen.RefreshType refreshType)
      throws IOException

This method will take the content from the back-buffer and move it into the front-buffer, making the changes visible to the terminal in the process. The graphics workflow with Screen would involve drawing text and text-like graphics on the back buffer and then finally calling refresh(..) to make it visible to the user.

Using this method call instead of refresh() gives you a little bit more control over how the screen will be refreshed.

Parameters:

refreshType - What type of refresh to do

Throws:

IOException - If there was an underlying I/O error

See Also:

Screen.RefreshType

doResizeIfNecessary

TerminalSize doResizeIfNecessary()

One problem working with Screens is that whenever the terminal is resized, the front and back buffers needs to be adjusted accordingly and the program should have a chance to figure out what to do with this extra space (or less space). The solution is to call, at the start of your rendering code, this method, which will check if the terminal has been resized and in that case update the internals of the Screen. After this call finishes, the screen's internal buffers will match the most recent size report from the underlying terminal.

Returns:

If the terminal has been resized since this method was last called, it will return the new size of the terminal. If not, it will return null.

scrollLines

void scrollLines(int firstLine,
                 int lastLine,
                 int distance)

Scroll a range of lines of this Screen according to given distance. Screen implementations of this method do not throw IOException.

Specified by:

scrollLines in interface Scrollable

Parameters:

firstLine - first line of the range to be scrolled (top line is 0)

lastLine - last (inclusive) line of the range to be scrolled

distance - if > 0: move lines up, else if < 0: move lines down.