xgb-window: add a basic xgb demo

Demonstrating RGBA visuals and direct pixel values.

prototypes/xgb-window.go

@@ -0,0 +1,133 @@
+package main
+
+import (
+	"github.com/BurntSushi/xgb"
+	"github.com/BurntSushi/xgb/xproto"
+	"log"
+	"math/rand"
+)
+
+func main() {
+	X, err := xgb.NewConn()
+	if err != nil {
+		log.Fatalln(err)
+	}
+
+	setup := xproto.Setup(X)
+	screen := setup.DefaultScreen(X)
+
+	var visual xproto.Visualid
+	var depth byte
+	for _, i := range screen.AllowedDepths {
+		if i.Depth == 32 {
+			// TODO: Could/should check other parameters.
+			for _, v := range i.Visuals {
+				if v.Class == xproto.VisualClassTrueColor {
+					visual = v.VisualId
+					depth = i.Depth
+					break
+				}
+			}
+		}
+	}
+	if visual == 0 {
+		log.Fatalln("cannot find an RGBA TrueColor visual")
+	}
+
+	mid, err := xproto.NewColormapId(X)
+	if err != nil {
+		log.Fatalln(err)
+	}
+
+	_ = xproto.CreateColormap(
+		X, xproto.ColormapAllocNone, mid, screen.Root, visual)
+
+	wid, err := xproto.NewWindowId(X)
+	if err != nil {
+		log.Fatalln(err)
+	}
+
+	// Border pixel and colormap are required when depth differs from parent.
+	_ = xproto.CreateWindow(X, depth, wid, screen.Root,
+		0, 0, 500, 500, 0, xproto.WindowClassInputOutput,
+		visual, xproto.CwBorderPixel|xproto.CwColormap,
+		[]uint32{0, uint32(mid)})
+
+	// This could be included in CreateWindow parameters.
+	_ = xproto.ChangeWindowAttributes(X, wid,
+		xproto.CwBackPixel|xproto.CwEventMask, []uint32{0x80808080,
+			xproto.EventMaskStructureNotify | xproto.EventMaskKeyPress |
+				xproto.EventMaskExposure})
+
+	title := "Gradient"
+	_ = xproto.ChangeProperty(X, xproto.PropModeReplace, wid, xproto.AtomWmName,
+		xproto.AtomString, 8, uint32(len(title)), []byte(title))
+
+	_ = xproto.MapWindow(X, wid)
+
+	cid, err := xproto.NewGcontextId(X)
+	if err != nil {
+		log.Fatalln(err)
+	}
+
+	_ = xproto.CreateGC(X, cid, xproto.Drawable(wid),
+		xproto.GcGraphicsExposures, []uint32{0})
+
+	var w, h uint16
+	var start, end uint32 = 0xabcdef, 0x32ab54
+	gradient := func() {
+		ra, ga, ba := (start>>16)&0xff, (start>>8)&0xff, start&0xff
+		rb, gb, bb := (end>>16)&0xff, (end>>8)&0xff, end&0xff
+
+		var low, high uint16 = 50, h - 50
+		if high > h {
+			return
+		}
+
+		for y := low; y < high; y++ {
+			ratio := float64(y-low) / (float64(high) - float64(low))
+			iratio := 1 - ratio
+
+			rR := uint32(ratio*float64(ra)+iratio*float64(rb)) & 0xff
+			gG := uint32(ratio*float64(ga)+iratio*float64(gb)) & 0xff
+			bB := uint32(ratio*float64(ba)+iratio*float64(bb)) & 0xff
+
+			_ = xproto.ChangeGC(X, cid, xproto.GcForeground,
+				[]uint32{0xff000000 | rR<<16 | gG<<8 | bB})
+			_ = xproto.PolyLine(X, xproto.CoordModeOrigin, xproto.Drawable(wid),
+				cid, []xproto.Point{
+					{X: 50, Y: int16(y)},
+					{X: int16(w - 50), Y: int16(y)},
+				})
+		}
+	}
+
+	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.ConfigureNotifyEvent:
+			w, h = e.Width, e.Height
+
+		case xproto.KeyPressEvent:
+			start = rand.Uint32() & 0xffffff
+			end = rand.Uint32() & 0xffffff
+			gradient()
+
+		case xproto.ExposeEvent:
+			gradient()
+		}
+	}
+
+}