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standard_renderer.go
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standard_renderer.go
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package tea
import (
"bytes"
"io"
"strings"
"sync"
"time"
"github.com/muesli/ansi/compressor"
"github.com/muesli/reflow/truncate"
)
const (
// defaultFramerate specifies the maximum interval at which we should
// update the view.
defaultFramerate = time.Second / 60
)
// standardRenderer is a framerate-based terminal renderer, updating the view
// at a given framerate to avoid overloading the terminal emulator.
//
// In cases where very high performance is needed the renderer can be told
// to exclude ranges of lines, allowing them to be written to directly.
type standardRenderer struct {
out io.Writer
buf bytes.Buffer
framerate time.Duration
ticker *time.Ticker
mtx *sync.Mutex
done chan struct{}
lastRender string
linesRendered int
useANSICompressor bool
once sync.Once
// essentially whether or not we're using the full size of the terminal
altScreenActive bool
// renderer dimensions; usually the size of the window
width int
height int
// lines explicitly set not to render
ignoreLines map[int]struct{}
}
// newRenderer creates a new renderer. Normally you'll want to initialize it
// with os.Stdout as the first argument.
func newRenderer(out io.Writer, mtx *sync.Mutex, useANSICompressor bool) renderer {
r := &standardRenderer{
out: out,
mtx: mtx,
framerate: defaultFramerate,
useANSICompressor: useANSICompressor,
}
if r.useANSICompressor {
r.out = &compressor.Writer{Forward: out}
}
return r
}
// start starts the renderer.
func (r *standardRenderer) start() {
if r.ticker == nil {
r.ticker = time.NewTicker(r.framerate)
}
r.done = make(chan struct{})
go r.listen()
}
// stop permanently halts the renderer, rendering the final frame.
func (r *standardRenderer) stop() {
r.flush()
clearLine(r.out)
r.once.Do(func() {
close(r.done)
})
if r.useANSICompressor {
if w, ok := r.out.(io.WriteCloser); ok {
_ = w.Close()
}
}
}
// kill halts the renderer. The final frame will not be rendered.
func (r *standardRenderer) kill() {
clearLine(r.out)
r.once.Do(func() {
close(r.done)
})
}
// listen waits for ticks on the ticker, or a signal to stop the renderer.
func (r *standardRenderer) listen() {
for {
select {
case <-r.ticker.C:
if r.ticker != nil {
r.flush()
}
case <-r.done:
r.ticker.Stop()
r.ticker = nil
return
}
}
}
// flush renders the buffer.
func (r *standardRenderer) flush() {
r.mtx.Lock()
defer r.mtx.Unlock()
if r.buf.Len() == 0 || r.buf.String() == r.lastRender {
// Nothing to do
return
}
// Output buffer
out := new(bytes.Buffer)
newLines := strings.Split(r.buf.String(), "\n")
oldLines := strings.Split(r.lastRender, "\n")
skipLines := make(map[int]struct{})
// Clear any lines we painted in the last render.
if r.linesRendered > 0 {
for i := r.linesRendered - 1; i > 0; i-- {
// If the number of lines we want to render hasn't increased and
// new line is the same as the old line we can skip rendering for
// this line as a performance optimization.
if (len(newLines) <= len(oldLines)) && (len(newLines) > i && len(oldLines) > i) && (newLines[i] == oldLines[i]) {
skipLines[i] = struct{}{}
} else if _, exists := r.ignoreLines[i]; !exists {
clearLine(out)
}
cursorUp(out)
}
if _, exists := r.ignoreLines[0]; !exists {
// We need to return to the start of the line here to properly
// erase it. Going back the entire width of the terminal will
// usually be farther than we need to go, but terminal emulators
// will stop the cursor at the start of the line as a rule.
//
// We use this sequence in particular because it's part of the ANSI
// standard (whereas others are proprietary to, say, VT100/VT52).
// If cursor previous line (ESC[ + <n> + F) were better supported
// we could use that above to eliminate this step.
cursorBack(out, r.width)
clearLine(out)
}
}
// Merge the set of lines we're skipping as a rendering optimization with
// the set of lines we've explicitly asked the renderer to ignore.
if r.ignoreLines != nil {
for k, v := range r.ignoreLines {
skipLines[k] = v
}
}
r.linesRendered = 0
// Paint new lines
for i := 0; i < len(newLines); i++ {
if _, skip := skipLines[r.linesRendered]; skip {
// Unless this is the last line, move the cursor down.
if i < len(newLines)-1 {
cursorDown(out)
}
} else {
line := newLines[i]
// Truncate lines wider than the width of the window to avoid
// wrapping, which will mess up rendering. If we don't have the
// width of the window this will be ignored.
//
// Note that on Windows we only get the width of the window on
// program initialization, so after a resize this won't perform
// correctly (signal SIGWINCH is not supported on Windows).
if r.width > 0 {
line = truncate.String(line, uint(r.width))
}
_, _ = io.WriteString(out, line)
if i < len(newLines)-1 {
_, _ = io.WriteString(out, "\r\n")
}
}
r.linesRendered++
}
// Make sure the cursor is at the start of the last line to keep rendering
// behavior consistent.
if r.altScreenActive {
// This case fixes a bug in macOS terminal. In other terminals the
// other case seems to do the job regardless of whether or not we're
// using the full terminal window.
moveCursor(out, r.linesRendered, 0)
} else {
cursorBack(out, r.width)
}
_, _ = r.out.Write(out.Bytes())
r.lastRender = r.buf.String()
r.buf.Reset()
}
// write writes to the internal buffer. The buffer will be outputted via the
// ticker which calls flush().
func (r *standardRenderer) write(s string) {
r.mtx.Lock()
defer r.mtx.Unlock()
r.buf.Reset()
// If an empty string was passed we should clear existing output and
// rendering nothing. Rather than introduce additional state to manage
// this, we render a single space as a simple (albeit less correct)
// solution.
if s == "" {
s = " "
}
_, _ = r.buf.WriteString(s)
}
func (r *standardRenderer) repaint() {
r.lastRender = ""
}
func (r *standardRenderer) altScreen() bool {
return r.altScreenActive
}
func (r *standardRenderer) setAltScreen(v bool) {
r.altScreenActive = v
r.repaint()
}
// setIgnoredLines specifies lines not to be touched by the standard Bubble Tea
// renderer.
func (r *standardRenderer) setIgnoredLines(from int, to int) {
// Lock if we're going to be clearing some lines since we don't want
// anything jacking our cursor.
if r.linesRendered > 0 {
r.mtx.Lock()
defer r.mtx.Unlock()
}
if r.ignoreLines == nil {
r.ignoreLines = make(map[int]struct{})
}
for i := from; i < to; i++ {
r.ignoreLines[i] = struct{}{}
}
// Erase ignored lines
if r.linesRendered > 0 {
out := new(bytes.Buffer)
for i := r.linesRendered - 1; i >= 0; i-- {
if _, exists := r.ignoreLines[i]; exists {
clearLine(out)
}
cursorUp(out)
}
moveCursor(out, r.linesRendered, 0) // put cursor back
_, _ = r.out.Write(out.Bytes())
}
}
// clearIgnoredLines returns control of any ignored lines to the standard
// Bubble Tea renderer. That is, any lines previously set to be ignored can be
// rendered to again.
func (r *standardRenderer) clearIgnoredLines() {
r.ignoreLines = nil
}
// insertTop effectively scrolls up. It inserts lines at the top of a given
// area designated to be a scrollable region, pushing everything else down.
// This is roughly how ncurses does it.
//
// To call this function use command ScrollUp().
//
// For this to work renderer.ignoreLines must be set to ignore the scrollable
// region since we are bypassing the normal Bubble Tea renderer here.
//
// Because this method relies on the terminal dimensions, it's only valid for
// full-window applications (generally those that use the alternate screen
// buffer).
//
// This method bypasses the normal rendering buffer and is philosophically
// different than the normal way we approach rendering in Bubble Tea. It's for
// use in high-performance rendering, such as a pager that could potentially
// be rendering very complicated ansi. In cases where the content is simpler
// standard Bubble Tea rendering should suffice.
func (r *standardRenderer) insertTop(lines []string, topBoundary, bottomBoundary int) {
r.mtx.Lock()
defer r.mtx.Unlock()
b := new(bytes.Buffer)
changeScrollingRegion(b, topBoundary, bottomBoundary)
moveCursor(b, topBoundary, 0)
insertLine(b, len(lines))
_, _ = io.WriteString(b, strings.Join(lines, "\r\n"))
changeScrollingRegion(b, 0, r.height)
// Move cursor back to where the main rendering routine expects it to be
moveCursor(b, r.linesRendered, 0)
_, _ = r.out.Write(b.Bytes())
}
// insertBottom effectively scrolls down. It inserts lines at the bottom of
// a given area designated to be a scrollable region, pushing everything else
// up. This is roughly how ncurses does it.
//
// To call this function use the command ScrollDown().
//
// See note in insertTop() for caveats, how this function only makes sense for
// full-window applications, and how it differs from the normal way we do
// rendering in Bubble Tea.
func (r *standardRenderer) insertBottom(lines []string, topBoundary, bottomBoundary int) {
r.mtx.Lock()
defer r.mtx.Unlock()
b := new(bytes.Buffer)
changeScrollingRegion(b, topBoundary, bottomBoundary)
moveCursor(b, bottomBoundary, 0)
_, _ = io.WriteString(b, "\r\n"+strings.Join(lines, "\r\n"))
changeScrollingRegion(b, 0, r.height)
// Move cursor back to where the main rendering routine expects it to be
moveCursor(b, r.linesRendered, 0)
_, _ = r.out.Write(b.Bytes())
}
// handleMessages handles internal messages for the renderer.
func (r *standardRenderer) handleMessages(msg Msg) {
switch msg := msg.(type) {
case repaintMsg:
// Force a repaint by clearing the render cache as we slide into a
// render.
r.repaint()
case WindowSizeMsg:
r.mtx.Lock()
r.width = msg.Width
r.height = msg.Height
r.mtx.Unlock()
case clearScrollAreaMsg:
r.clearIgnoredLines()
// Force a repaint on the area where the scrollable stuff was in this
// update cycle
r.mtx.Lock()
r.lastRender = ""
r.mtx.Unlock()
case syncScrollAreaMsg:
// Re-render scrolling area
r.clearIgnoredLines()
r.setIgnoredLines(msg.topBoundary, msg.bottomBoundary)
r.insertTop(msg.lines, msg.topBoundary, msg.bottomBoundary)
// Force non-scrolling stuff to repaint in this update cycle
r.mtx.Lock()
r.lastRender = ""
r.mtx.Unlock()
case scrollUpMsg:
r.insertTop(msg.lines, msg.topBoundary, msg.bottomBoundary)
case scrollDownMsg:
r.insertBottom(msg.lines, msg.topBoundary, msg.bottomBoundary)
}
}
// HIGH-PERFORMANCE RENDERING STUFF
type syncScrollAreaMsg struct {
lines []string
topBoundary int
bottomBoundary int
}
// SyncScrollArea performs a paint of the entire region designated to be the
// scrollable area. This is required to initialize the scrollable region and
// should also be called on resize (WindowSizeMsg).
//
// For high-performance, scroll-based rendering only.
func SyncScrollArea(lines []string, topBoundary int, bottomBoundary int) Cmd {
return func() Msg {
return syncScrollAreaMsg{
lines: lines,
topBoundary: topBoundary,
bottomBoundary: bottomBoundary,
}
}
}
type clearScrollAreaMsg struct{}
// ClearScrollArea deallocates the scrollable region and returns the control of
// those lines to the main rendering routine.
//
// For high-performance, scroll-based rendering only.
func ClearScrollArea() Msg {
return clearScrollAreaMsg{}
}
type scrollUpMsg struct {
lines []string
topBoundary int
bottomBoundary int
}
// ScrollUp adds lines to the top of the scrollable region, pushing existing
// lines below down. Lines that are pushed out the scrollable region disappear
// from view.
//
// For high-performance, scroll-based rendering only.
func ScrollUp(newLines []string, topBoundary, bottomBoundary int) Cmd {
return func() Msg {
return scrollUpMsg{
lines: newLines,
topBoundary: topBoundary,
bottomBoundary: bottomBoundary,
}
}
}
type scrollDownMsg struct {
lines []string
topBoundary int
bottomBoundary int
}
// ScrollDown adds lines to the bottom of the scrollable region, pushing
// existing lines above up. Lines that are pushed out of the scrollable region
// disappear from view.
//
// For high-performance, scroll-based rendering only.
func ScrollDown(newLines []string, topBoundary, bottomBoundary int) Cmd {
return func() Msg {
return scrollDownMsg{
lines: newLines,
topBoundary: topBoundary,
bottomBoundary: bottomBoundary,
}
}
}