Controls

examples/getcontrols.go

@@ -0,0 +1,20 @@
+// Example program that reads the list of available controls and prints them.
+package main
+
+import "github.com/blackjack/webcam"
+import "fmt"
+
+func main() {
+	cam, err := webcam.Open("/dev/video0")
+	if err != nil {
+		panic(err.Error())
+	}
+	defer cam.Close()
+
+    clist := cam.GetControlList()
+
+	fmt.Println("Available controls: ")
+    for _, c := range clist {
+        fmt.Printf("%32s  Min: %4d  Max: %5d\n", c.Name, c.Min, c.Max)
+    }
+}

ioctl/ioctl.go

@@ -21,6 +21,8 @@ const (
 	typeShift      = numberShift + numberBits
 	sizeShift      = typeShift + typeBits
 	directionShift = sizeShift + sizeBits
+
+	ErrEINVAL = unix.EINVAL
 )
 
 func ioc(dir, t, nr, size uintptr) uintptr {

v4l2.go

@@ -3,12 +3,28 @@ package webcam
 import (
 	"bytes"
 	"encoding/binary"
+	"strings"
 	"unsafe"
 
 	"github.com/blackjack/webcam/ioctl"
 	"golang.org/x/sys/unix"
 )
 
+type controlType int
+
+const (
+	c_int controlType = iota
+	c_bool
+	c_menu
+)
+
+type control struct {
+	id     uint32
+	c_type controlType
+	min    int32
+	max    int32
+}
+
 const (
 	V4L2_CAP_VIDEO_CAPTURE      uint32 = 0x00000001
 	V4L2_CAP_STREAMING          uint32 = 0x04000000
@@ -29,6 +45,28 @@ const (
 	V4L2_CID_PRIVATE_BASE       uint32 = 0x08000000
 )
 
+const (
+	V4L2_CTRL_TYPE_INTEGER      uint32 = 1
+	V4L2_CTRL_TYPE_BOOLEAN      uint32 = 2
+	V4L2_CTRL_TYPE_MENU         uint32 = 3
+	V4L2_CTRL_TYPE_BUTTON       uint32 = 4
+	V4L2_CTRL_TYPE_INTEGER64    uint32 = 5
+	V4L2_CTRL_TYPE_CTRL_CLASS   uint32 = 6
+	V4L2_CTRL_TYPE_STRING       uint32 = 7
+	V4L2_CTRL_TYPE_BITMASK      uint32 = 8
+	V4L2_CTRL_TYPE_INTEGER_MENU uint32 = 9
+
+	V4L2_CTRL_COMPOUND_TYPES uint32 = 0x0100
+	V4L2_CTRL_TYPE_U8        uint32 = 0x0100
+	V4L2_CTRL_TYPE_U16       uint32 = 0x0101
+	V4L2_CTRL_TYPE_U32       uint32 = 0x0102
+)
+
+const (
+	V4L2_CTRL_FLAG_DISABLED  uint32 = 0x00000001
+	V4L2_CTRL_FLAG_NEXT_CTRL uint32 = 0x80000000
+)
+
 var (
 	VIDIOC_QUERYCAP  = ioctl.IoR(uintptr('V'), 0, unsafe.Sizeof(v4l2_capability{}))
 	VIDIOC_ENUM_FMT  = ioctl.IoRW(uintptr('V'), 2, unsafe.Sizeof(v4l2_fmtdesc{}))
@@ -37,6 +75,7 @@ var (
 	VIDIOC_QUERYBUF  = ioctl.IoRW(uintptr('V'), 9, unsafe.Sizeof(v4l2_buffer{}))
 	VIDIOC_QBUF      = ioctl.IoRW(uintptr('V'), 15, unsafe.Sizeof(v4l2_buffer{}))
 	VIDIOC_DQBUF     = ioctl.IoRW(uintptr('V'), 17, unsafe.Sizeof(v4l2_buffer{}))
+	VIDIOC_G_CTRL    = ioctl.IoRW(uintptr('V'), 27, unsafe.Sizeof(v4l2_control{}))
 	VIDIOC_S_CTRL    = ioctl.IoRW(uintptr('V'), 28, unsafe.Sizeof(v4l2_control{}))
 	VIDIOC_QUERYCTRL = ioctl.IoRW(uintptr('V'), 36, unsafe.Sizeof(v4l2_queryctrl{}))
 	//sizeof int32
@@ -418,28 +457,52 @@ func waitForFrame(fd uintptr, timeout uint32) (count int, err error) {
 
 }
 
+func getControl(fd uintptr, id uint32) (int32, error) {
+	ctrl := &v4l2_control{}
+	ctrl.id = id
+	err := ioctl.Ioctl(fd, VIDIOC_G_CTRL, uintptr(unsafe.Pointer(ctrl)))
+	return ctrl.value, err
+}
+
 func setControl(fd uintptr, id uint32, val int32) error {
 	ctrl := &v4l2_control{}
 	ctrl.id = id
 	ctrl.value = val
 	return ioctl.Ioctl(fd, VIDIOC_S_CTRL, uintptr(unsafe.Pointer(ctrl)))
 }
 
-func getControls(fd uintptr) map[uint32]string {
-	query := &v4l2_queryctrl{}
-	var controls map[uint32]string
+func queryControls(fd uintptr) map[string]control {
+	var controls map[string]control = make(map[string]control)
 	var err error
-	for query.id = V4L2_CID_BASE; err == nil; query.id++ {
-		err = ioctl.Ioctl(fd, VIDIOC_QUERYCTRL, uintptr(unsafe.Pointer(query)))
-		if err == nil {
-			controls[query.id] = CToGoString(query.name[:])
-		}
-	}
-	err = nil
-	for query.id = V4L2_CID_PRIVATE_BASE; err == nil; query.id++ {
+	// Don't use V42L_CID_BASE since it is the same as brightness.
+	var id uint32
+	for err != ioctl.ErrEINVAL {
+		id |= V4L2_CTRL_FLAG_NEXT_CTRL
+		query := &v4l2_queryctrl{}
+		query.id = id
 		err = ioctl.Ioctl(fd, VIDIOC_QUERYCTRL, uintptr(unsafe.Pointer(query)))
+		id = query.id
 		if err == nil {
-			controls[query.id] = CToGoString(query.name[:])
+			if (query.flags & V4L2_CTRL_FLAG_DISABLED) != 0 {
+				continue
+			}
+			var c control
+			switch query._type {
+			default:
+				continue
+			case V4L2_CTRL_TYPE_INTEGER, V4L2_CTRL_TYPE_INTEGER64:
+				c.c_type = c_int
+			case V4L2_CTRL_TYPE_BOOLEAN:
+				c.c_type = c_bool
+			case V4L2_CTRL_TYPE_MENU:
+				c.c_type = c_menu
+			}
+			c.id = id
+			c.min = query.minimum
+			c.max = query.maximum
+			// Normalise name (' ' -> '_', make lower case).
+			n := strings.Replace(strings.ToLower(CToGoString(query.name[:])), " ", "_", -1)
+			controls[n] = c
 		}
 	}
 	return controls

webcam.go

@@ -16,6 +16,13 @@ type Webcam struct {
 	bufcount  uint32
 	buffers   [][]byte
 	streaming bool
+	controls  map[string]control
+}
+
+type Control struct {
+	Name string
+	Min  int32
+	Max  int32
 }
 
 // Open a webcam with a given path
@@ -126,6 +133,47 @@ func (w *Webcam) SetBufferCount(count uint32) error {
 	return nil
 }
 
+// Get the list of available controls.
+func (w *Webcam) GetControlList() []Control {
+	var clist []Control
+	if len(w.controls) == 0 {
+		w.controls = queryControls(w.fd)
+	}
+	for s, c := range w.controls {
+		clist = append(clist, Control{s, c.min, c.max})
+	}
+	return clist
+}
+
+// Get the value of a control.
+func (w *Webcam) GetControl(name string) (int32, error) {
+	c, err := w.lookupControl(name)
+	if err != nil {
+		return 0, err
+	}
+	return getControl(w.fd, c.id)
+}
+
+// Set a control.
+func (w *Webcam) SetControl(name string, value int32) error {
+	c, err := w.lookupControl(name)
+	if err != nil {
+		return err
+	}
+	return setControl(w.fd, c.id, value)
+}
+
+func (w *Webcam) lookupControl(name string) (control, error) {
+	if len(w.controls) == 0 {
+		w.controls = queryControls(w.fd)
+	}
+	c, ok := w.controls[name]
+	if !ok {
+		return control{}, errors.New("Unknown control: " + name)
+	}
+	return c, nil
+}
+
 // Start streaming process
 func (w *Webcam) StartStreaming() error {
 	if w.streaming {