Controls

examples/getcontrols/getcontrols.go

@@ -0,0 +1,40 @@
+// Example program that reads the list of available controls and prints them.
+package main
+
+import (
+	"flag"
+	"fmt"
+
+	"github.com/blackjack/webcam"
+)
+
+var device = flag.String("input", "/dev/video0", "Input video device")
+
+func main() {
+	flag.Parse()
+	cam, err := webcam.Open(*device)
+	if err != nil {
+		panic(err.Error())
+	}
+	defer cam.Close()
+
+	fmap := cam.GetSupportedFormats()
+	fmt.Println("Available Formats: ")
+	for p, s := range fmap {
+		var pix []byte
+		for i := 0; i < 4; i++ {
+			pix = append(pix, byte(p>>uint(i*8)))
+		}
+		fmt.Printf("ID:%08x ('%s') %s\n   ", p, pix, s)
+		for _, fs := range cam.GetSupportedFrameSizes(p) {
+			fmt.Printf(" %s", fs.GetString())
+		}
+		fmt.Printf("\n")
+	}
+
+	cmap := cam.GetControls()
+	fmt.Println("Available controls: ")
+	for id, c := range cmap {
+		fmt.Printf("ID:%08x %-32s  Min: %4d  Max: %5d\n", id, c.Name, c.Min, c.Max)
+	}
+}

v4l2.go

@@ -9,6 +9,22 @@ import (
 	"golang.org/x/sys/unix"
 )
 
+type controlType int
+
+const (
+	c_int controlType = iota
+	c_bool
+	c_menu
+)
+
+type control struct {
+	id     uint32
+	name   string
+	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 +457,51 @@ 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) []control {
+	controls := []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 == nil {
+		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.name = CToGoString(query.name[:])
+			c.min = query.minimum
+			c.max = query.maximum
+			controls = append(controls, c)
 		}
 	}
 	return controls

webcam.go

@@ -18,6 +18,14 @@ type Webcam struct {
 	streaming bool
 }
 
+type ControlID uint32
+
+type Control struct {
+	Name string
+	Min  int32
+	Max  int32
+}
+
 // Open a webcam with a given path
 // Checks if device is a v4l2 device and if it is
 // capable to stream video
@@ -126,6 +134,25 @@ func (w *Webcam) SetBufferCount(count uint32) error {
 	return nil
 }
 
+// Get a map of available controls.
+func (w *Webcam) GetControls() map[ControlID]Control {
+	cmap := make(map[ControlID]Control)
+	for _, c := range queryControls(w.fd) {
+		cmap[ControlID(c.id)] = Control{c.name, c.min, c.max}
+	}
+	return cmap
+}
+
+// Get the value of a control.
+func (w *Webcam) GetControl(id ControlID) (int32, error) {
+	return getControl(w.fd, uint32(id))
+}
+
+// Set a control.
+func (w *Webcam) SetControl(id ControlID, value int32) error {
+	return setControl(w.fd, uint32(id), value)
+}
+
 // Start streaming process
 func (w *Webcam) StartStreaming() error {
 	if w.streaming {