xgb-draw: add a demo drawing application

Just trying to see how fast XRender can be and such.

prototypes/xgb-draw.go

@@ -0,0 +1,141 @@
+package main
+
+import (
+	"github.com/BurntSushi/xgb"
+	"github.com/BurntSushi/xgb/render"
+	"github.com/BurntSushi/xgb/xproto"
+	"log"
+)
+
+func F64ToFixed(f float64) render.Fixed { return render.Fixed(f * 65536) }
+func FixedToF64(f render.Fixed) float64 { return float64(f) / 65536 }
+
+func main() {
+	X, err := xgb.NewConn()
+	if err != nil {
+		log.Fatalln(err)
+	}
+	if err := render.Init(X); err != nil {
+		log.Fatalln(err)
+	}
+
+	setup := xproto.Setup(X)
+	screen := setup.DefaultScreen(X)
+
+	visual, depth := screen.RootVisual, screen.RootDepth
+	if depth < 24 {
+		log.Fatalln("need more colors")
+	}
+
+	wid, err := xproto.NewWindowId(X)
+	if err != nil {
+		log.Fatalln(err)
+	}
+
+	_ = xproto.CreateWindow(X, depth, wid, screen.Root,
+		0, 0, 500, 500, 0, xproto.WindowClassInputOutput,
+		visual, xproto.CwBackPixel|xproto.CwEventMask,
+		[]uint32{0xffffffff, xproto.EventMaskButtonPress |
+			xproto.EventMaskButtonMotion | xproto.EventMaskButtonRelease |
+			xproto.EventMaskStructureNotify})
+
+	title := []byte("Draw")
+	_ = xproto.ChangeProperty(X, xproto.PropModeReplace, wid, xproto.AtomWmName,
+		xproto.AtomString, 8, uint32(len(title)), title)
+
+	_ = xproto.MapWindow(X, wid)
+
+	pformats, err := render.QueryPictFormats(X).Reply()
+	if err != nil {
+		log.Fatalln(err)
+	}
+
+	var pformat render.Pictformat
+	for _, pd := range pformats.Screens[X.DefaultScreen].Depths {
+		for _, pv := range pd.Visuals {
+			if pv.Visual == visual {
+				pformat = pv.Format
+			}
+		}
+	}
+
+	pid, err := render.NewPictureId(X)
+	if err != nil {
+		log.Fatalln(err)
+	}
+	render.CreatePicture(X, pid, xproto.Drawable(wid), pformat, 0, []uint32{})
+
+	// Brush shape.
+	brushid, err := render.NewPictureId(X)
+	if err != nil {
+		log.Fatalln(err)
+	}
+
+	cFull := render.Color{0xffff, 0xffff, 0xffff, 0xffff}
+	cTrans := render.Color{0xffff, 0xffff, 0xffff, 0}
+	_ = render.CreateRadialGradient(X, brushid,
+		render.Pointfix{F64ToFixed(50), F64ToFixed(50)},
+		render.Pointfix{F64ToFixed(50), F64ToFixed(50)},
+		F64ToFixed(0),
+		F64ToFixed(50),
+		2, []render.Fixed{F64ToFixed(0), F64ToFixed(1)},
+		[]render.Color{cFull, cTrans})
+
+	// Brush color.
+	colorid, err := render.NewPictureId(X)
+	if err != nil {
+		log.Fatalln(err)
+	}
+	_ = render.CreateSolidFill(X, colorid, render.Color{
+		Red:   0xcccc,
+		Green: 0xaaaa,
+		Blue:  0x8888,
+		Alpha: 0xffff,
+	})
+
+	// Unfortunately, XRender won't give us any /blending operators/, only
+	// providing basic Porter-Duff ones with useless disjoint/conjoint variants,
+	// but we need the "lighten" operator to draw brush strokes properly.
+	//
+	// https://www.cairographics.org/operators/
+	// http://ssp.impulsetrain.com/porterduff.html
+	printAt := func(x, y int16) {
+		_ = render.Composite(X, render.PictOpOver,
+			colorid, brushid, pid,
+			0, 0, 0, 0, x-50, y-50, 100, 100)
+	}
+
+	drawing := false
+	for {
+		ev, xerr := X.WaitForEvent()
+		if xerr != nil {
+			log.Printf("Error: %s\n", xerr)
+			return
+		}
+		if ev == nil {
+			return
+		}
+
+		log.Printf("Event: %s\n", ev)
+		switch e := ev.(type) {
+		case xproto.UnmapNotifyEvent:
+			return
+
+		case xproto.ButtonPressEvent:
+			if e.Detail == xproto.ButtonIndex1 {
+				drawing = true
+				printAt(e.EventX, e.EventY)
+			}
+
+		case xproto.MotionNotifyEvent:
+			if drawing {
+				printAt(e.EventX, e.EventY)
+			}
+
+		case xproto.ButtonReleaseEvent:
+			if e.Detail == xproto.ButtonIndex1 {
+				drawing = false
+			}
+		}
+	}
+}