gui: a /dev/draw layer in go, with no cgo and no devdraw

9fans.net/go/draw builds for plan9 but shells out to plan9port's
devdraw, which 9front does not have. This talks to /dev/draw itself:
the protocol is file i/o, so a pure-go client is a few hundred lines
under an already-complete idea.

draw/keyboard.go opens /dev/cons and turns the console raw, as
libdraw's initkeyboard does. Without it rio keeps its line editor on
the window and paints what you type over the drawing.

draw/snarf.go writes /dev/snarf, which is what every other program on
the system means by copy.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

1 files changed, 74 insertions, 0 deletions

diff --git a/gui/draw/mouse.go b/gui/draw/mouse.go
new file mode 100644
index 0000000..a4ddf63
--- /dev/null
+++ b/gui/draw/mouse.go
@@ -0,0 +1,74 @@
+package draw
+
+import (
+	"fmt"
+	"os"
+	"strconv"
+)
+
+// Mouse is one record from /dev/mouse.
+type Mouse struct {
+	Point
+	Buttons int
+	Msec    uint32
+}
+
+// Mousectl delivers mouse and resize events on channels.  This is the shape
+// libdraw's Mousectl already has -- it is hand-rolled CSP in C because there
+// were no goroutines.  Here it is what the language does natively.
+type Mousectl struct {
+	C      <-chan Mouse
+	Resize <-chan struct{}
+
+	f *os.File
+}
+
+func OpenMouse(dev string) (*Mousectl, error) {
+	if dev == "" {
+		dev = "/dev"
+	}
+	f, err := os.OpenFile(dev+"/mouse", os.O_RDWR, 0)
+	if err != nil {
+		return nil, fmt.Errorf("open mouse: %w", err)
+	}
+	c := make(chan Mouse)
+	rc := make(chan struct{}, 1)
+	mc := &Mousectl{C: c, Resize: rc, f: f}
+	// One goroutine parked in read(2).  Plan 9 has no netpoll in the Go
+	// runtime, so this pins an OS thread for as long as it blocks -- fine
+	// for the two or three event sources a UI has, not for hundreds.
+	go func() {
+		defer close(c)
+		buf := make([]byte, 1+5*12)
+		for {
+			n, err := f.Read(buf)
+			if err != nil {
+				return
+			}
+			if n != 1+4*12 {
+				continue
+			}
+			fld := func(i int) int {
+				v, _ := strconv.Atoi(trim(string(buf[1+i*12 : 1+i*12+12])))
+				return v
+			}
+			switch buf[0] {
+			case 'r':
+				select {
+				case rc <- struct{}{}:
+				default:
+				}
+				fallthrough
+			case 'm':
+				c <- Mouse{
+					Point:   Point{int32(fld(0)), int32(fld(1))},
+					Buttons: fld(2),
+					Msec:    uint32(fld(3)),
+				}
+			}
+		}
+	}()
+	return mc, nil
+}
+
+func (mc *Mousectl) Close() error { return mc.f.Close() }