haven/nexgb/examples/create-window/main.go

// Example create-window shows how to create a window, map it, resize it,
// and listen to structure and key events (i.e., when the window is resized
// by the window manager, or when key presses/releases are made when the
// window has focus). The events are printed to stdout.
package main

import (
	"fmt"

	xgb "janouch.name/haven/nexgb"
	"janouch.name/haven/nexgb/xproto"
)

func main() {
	X, err := xgb.NewConn()
	if err != nil {
		fmt.Println(err)
		return
	}

	// xproto.Setup retrieves the Setup information from the setup bytes
	// gathered during connection.
	setup := xproto.Setup(X)

	// This is the default screen with all its associated info.
	screen := setup.DefaultScreen(X)

	// Any time a new resource (i.e., a window, pixmap, graphics context, etc.)
	// is created, we need to generate a resource identifier.
	// If the resource is a window, then use xproto.NewWindowId. If it's for
	// a pixmap, then use xproto.NewPixmapId. And so on...
	wid, _ := xproto.NewWindowId(X)

	// CreateWindow takes a boatload of parameters.
	xproto.CreateWindow(X, screen.RootDepth, wid, screen.Root,
		0, 0, 500, 500, 0,
		xproto.WindowClassInputOutput, screen.RootVisual, 0, []uint32{})

	// This call to ChangeWindowAttributes could be factored out and
	// included with the above CreateWindow call, but it is left here for
	// instructive purposes. It tells X to send us events when the 'structure'
	// of the window is changed (i.e., when it is resized, mapped, unmapped,
	// etc.) and when a key press or a key release has been made when the
	// window has focus.
	// We also set the 'BackPixel' to white so that the window isn't butt ugly.
	xproto.ChangeWindowAttributes(X, wid,
		xproto.CwBackPixel|xproto.CwEventMask,
		[]uint32{ // values must be in the order defined by the protocol
			0xffffffff,
			xproto.EventMaskStructureNotify |
				xproto.EventMaskKeyPress |
				xproto.EventMaskKeyRelease})

	// MapWindow makes the window we've created appear on the screen.
	// We demonstrated the use of a 'checked' request here.
	// A checked request is a fancy way of saying, "do error handling
	// synchronously." Namely, if there is a problem with the MapWindow request,
	// we'll get the error *here*. If we were to do a normal unchecked
	// request (like the above CreateWindow and ChangeWindowAttributes
	// requests), then we would only see the error arrive in the main event
	// loop.
	//
	// Typically, checked requests are useful when you need to make sure they
	// succeed. Since they are synchronous, they incur a round trip cost before
	// the program can continue, but this is only going to be noticeable if
	// you're issuing tons of requests in succession.
	//
	// Note that requests without replies are by default unchecked while
	// requests *with* replies are checked by default.
	err = xproto.MapWindowChecked(X, wid).Check()
	if err != nil {
		fmt.Printf("Checked Error for mapping window %d: %s\n", wid, err)
	} else {
		fmt.Printf("Map window %d successful!\n", wid)
	}

	// This is an example of an invalid MapWindow request and what an error
	// looks like.
	err = xproto.MapWindowChecked(X, 0).Check()
	if err != nil {
		fmt.Printf("Checked Error for mapping window 0x1: %s\n", err)
	} else { // neva
		fmt.Printf("Map window 0x1 successful!\n")
	}

	// Start the main event loop.
	for {
		// WaitForEvent either returns an event or an error and never both.
		// If both are nil, then something went wrong and the loop should be
		// halted.
		//
		// An error can only be seen here as a response to an unchecked
		// request.
		ev, xerr := X.WaitForEvent()
		if ev == nil && xerr == nil {
			fmt.Println("Both event and error are nil. Exiting...")
			return
		}

		if ev != nil {
			fmt.Printf("Event: %s\n", ev)
		}
		if xerr != nil {
			fmt.Printf("Error: %s\n", xerr)
		}
	}
}