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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
}
}
}
}
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