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// Package render renders to the terminal using ANSI escape sequences.
package render
import (
"bufio"
"bytes"
"fmt"
"os"
)
// 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
}
// 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() {
if r.prevLines > 0 {
fmt.Fprintf(&r.w, "\033[%dA", r.prevLines)
}
r.prevLines = 0
r.w.WriteString("\r")
}
// 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 {
n, err := r.w.Write(buf)
totalBytes += n
return totalBytes, err
}
line := buf[:i]
buf = buf[i+1:]
n, err := r.w.Write(line)
totalBytes += n
if err != nil {
return totalBytes, err
}
if _, err := r.w.WriteString("\033[K\n"); err != nil {
return totalBytes, err
}
totalBytes++
r.prevLines++
}
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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