gst: add get request pad function (#16)

* gst: add get request pad function

* gst: add an example of GetReuqestPad()

* gst: remove pad=nil on ReleaseRequestPad

examples/requestpad/main.go

@@ -0,0 +1,159 @@
+package main
+
+import (
+	"errors"
+	"fmt"
+	"github.com/tinyzimmer/go-glib/glib"
+	"github.com/tinyzimmer/go-gst/examples"
+	"github.com/tinyzimmer/go-gst/gst"
+	"os"
+	"time"
+)
+
+type workflow struct {
+	*gst.Pipeline
+}
+
+func (w *workflow) newSrc() {
+	src, err := gst.NewElementWithName("videotestsrc", "src2")
+	if err != nil {
+		fmt.Printf("err %v\n", err)
+		return
+	}
+	src.Set("is-live", true)
+	w.Add(src)
+
+	caps, err := gst.NewElementWithName("capsfilter", "caps2")
+	if err != nil {
+		fmt.Printf("err %v\n", err)
+		return
+	}
+	caps.Set("caps", gst.NewCapsFromString("video/x-raw , width=640, height=360"))
+	w.Add(caps)
+
+	src.Link(caps)
+
+	// Get a sink pad on compositor
+	mixer, err := w.GetElementByName("mixer")
+	if err != nil {
+		fmt.Printf("err %v\n", err)
+		return
+	}
+	pad := mixer.GetRequestPad("sink_%u")
+	pad.SetProperty("xpos", 640)
+	pad.SetProperty("ypos", 0)
+
+	caps.GetStaticPad("src").Link(pad)
+	caps.SyncStateWithParent()
+	src.SyncStateWithParent()
+
+}
+func (w *workflow) delSrc() {
+
+	mixer, err := w.GetElementByName("mixer")
+	if err != nil {
+		fmt.Printf("err %v\n", err)
+		return
+	}
+
+	src, err := w.GetElementByName("src2")
+	if err != nil {
+		fmt.Printf("err %v\n", err)
+		return
+	}
+	caps, err := w.GetElementByName("caps2")
+	if err != nil {
+		fmt.Printf("err %v\n", err)
+		return
+	}
+	pad := mixer.GetStaticPad("sink_1")
+	if pad == nil {
+		fmt.Printf("pad is null\n")
+		return
+	}
+
+	src.SetState(gst.StateNull)
+	caps.SetState(gst.StateNull)
+
+	w.Remove(src)
+	w.Remove(caps)
+	mixer.ReleaseRequestPad(pad)
+}
+
+func createPipeline() (*gst.Pipeline, error) {
+	gst.Init(nil)
+	var err error
+	var w workflow
+	w.Pipeline, err = gst.NewPipeline("")
+	if err != nil {
+		fmt.Println(err)
+		os.Exit(2)
+	}
+	elements, err := gst.NewElementMany("videotestsrc", "capsfilter", "compositor", "autovideosink")
+	caps := elements[1]
+	caps.SetProperty("caps", gst.NewCapsFromString("video/x-raw , width=640, height=360"))
+	caps.SetProperty("name", "caps1")
+	mixer := elements[2]
+	mixer.SetProperty("name", "mixer")
+	if err != nil {
+		fmt.Printf("err %v\n", err)
+		return nil, err
+	}
+	w.AddMany(elements...)
+	gst.ElementLinkMany(elements...)
+
+	go func() {
+		time.Sleep(time.Second)
+		w.newSrc()
+		time.Sleep(time.Second)
+		w.delSrc()
+		//runtime.GC()
+	}()
+
+	return w.Pipeline, nil
+}
+
+func runPipeline(loop *glib.MainLoop, pipeline *gst.Pipeline) error {
+	// Start the pipeline
+	pipeline.SetState(gst.StatePlaying)
+
+	// Add a message watch to the bus to quit on any error
+	pipeline.GetPipelineBus().AddWatch(func(msg *gst.Message) bool {
+		var err error
+
+		// If the stream has ended or any element posts an error to the
+		// bus, populate error.
+		switch msg.Type() {
+		case gst.MessageEOS:
+			err = errors.New("end-of-stream")
+		case gst.MessageError:
+			// The parsed error implements the error interface, but also
+			// contains additional debug information.
+			gerr := msg.ParseError()
+			fmt.Println("go-gst-debug:", gerr.DebugString())
+			err = gerr
+		}
+
+		// If either condition triggered an error, log and quit
+		if err != nil {
+			fmt.Println("ERROR:", err.Error())
+			loop.Quit()
+			return false
+		}
+
+		return true
+	})
+
+	// Block on the main loop
+	return loop.RunError()
+}
+
+func main() {
+	examples.RunLoop(func(loop *glib.MainLoop) error {
+		pipeline, err := createPipeline()
+		if err != nil {
+			return err
+		}
+		return runPipeline(loop, pipeline)
+	})
+}

gst/gst_element.go

@@ -501,3 +501,21 @@ func (e *Element) URIHandler() URIHandler {
 func (e *Element) RemovePad(pad *Pad) bool {
 	return gobool(C.gst_element_remove_pad(e.Instance(), pad.Instance()))
 }
+
+// GetRequestPad gets a request pad from the element based on the name of the pad template.
+// Unlike static pads, request pads are not created automatically but are only created on demand
+// For example, audiomixer has sink template, 'sink_%u', which is used for creating multiple sink pads on demand so that it performs mixing of audio streams by linking multiple upstream elements on it's sink pads created on demand.
+// This returns the request pad created on demand. Otherwise, it returns null if failed to create.
+func (e *Element) GetRequestPad(name string) *Pad {
+       cname := C.CString(name)
+       defer C.free(unsafe.Pointer(cname))
+       pad := C.gst_element_get_request_pad(e.Instance(), (*C.gchar)(unsafe.Pointer(cname)))
+       if pad == nil {
+               return nil
+       }
+       return FromGstPadUnsafeFull(unsafe.Pointer(pad))
+}
+// ReleaseRequestPad releases request pad
+func (e *Element) ReleaseRequestPad(pad *Pad) {
+       C.gst_element_release_request_pad(e.Instance(), pad.Instance())
+}