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// Package render renders to the terminal using ANSI escape sequences.
package render
import (
"bufio"
"bytes"
"fmt"
"os"
"unicode/utf8"
)
// Renderer updates a terminal UI. Typical usage looks like
//
// r := render.New()
// // Game loop
// for {
// // Update state
//
// r.Clear()
// fmt.Fprintf(r, "Render UI by writing to r using io.Writer")
// r.Flush()
// }
type Renderer struct {
w bufio.Writer
prevLines int
width int
partialLineLen int
}
// New creates a new Renderer
func New() *Renderer {
r := &Renderer{}
r.w.Reset(os.Stderr)
return r
}
// Clear clears the screen before rendering a new frame.
func (r *Renderer) Clear(width int) {
r.width = width
if r.prevLines > 0 {
fmt.Fprintf(&r.w, "\033[%dA", r.prevLines)
}
r.w.WriteString("\r")
r.prevLines = 0
r.partialLineLen = 0
}
func truncate(b []byte, width int) ([]byte, int) {
n := 0
for i := 0; i < len(b); {
if bytes.HasPrefix(b[i:], []byte("\033[")) {
// An escape sequence usually starts with [, then has one or two numbers
// separated by semicolon, and ends with some terminating character. To
// try and munch the whole sequence, skip over any numbers and
// semicolon here.
for i += 2; i < len(b)-1 && ('0' <= b[i] && b[i] <= '9' || b[i] == ';'); i++ {
}
// Skip the terminating character.
i++
continue
}
if n+1 > width {
return b[:i], n
}
_, runeWidth := utf8.DecodeRune(b[i:])
i += runeWidth
n++
}
return b, n
}
// Write implements io.Writer.
func (r *Renderer) Write(buf []byte) (int, error) {
totalBytes := 0
for len(buf) > 0 {
i := bytes.IndexByte(buf, '\n')
if i < 0 {
line, lineWidth := truncate(buf, r.width-r.partialLineLen)
r.partialLineLen += lineWidth
if n, err := r.w.Write(line); err != nil {
return totalBytes + n, err
}
totalBytes += len(buf)
return totalBytes, nil
}
line, _ := truncate(buf[:i], r.width)
buf = buf[i+1:]
if n, err := r.w.Write(line); err != nil {
return totalBytes + n, err
}
totalBytes += i
if _, err := r.w.WriteString("\033[K\n"); err != nil {
return totalBytes, err
}
totalBytes++
r.prevLines++
r.partialLineLen = 0
}
return totalBytes, nil
}
// Flush flushes the internal buffer to stdout. Flush should be called at the
// end of every frame.
func (r *Renderer) Flush() {
r.w.WriteString("\033[J")
r.w.Flush()
}
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