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xgb-draw: proper brush stroke render

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This commit is contained in:
Přemysl Eric Janouch
2018-09-04 19:22:32 +02:00
parent df082e1dee
commit 254ceb810c
1 changed files with 143 additions and 20 deletions
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163
prototypes/xgb-draw.go
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@@ -1,3 +1,10 @@
// Network-friendly drawing application based on XRender.
//
// TODO
// - interpolate motion between points
// - use double buffering to remove flicker
// (more pronounced over X11 forwarding)
// - maybe keep the pixmap as large as the window
package main
import (
@@ -10,6 +17,16 @@ import (
func F64ToFixed(f float64) render.Fixed { return render.Fixed(f * 65536) }
func FixedToF64(f render.Fixed) float64 { return float64(f) / 65536 }
func findPictureFormat(formats []render.Pictforminfo,
depth byte, direct render.Directformat) render.Pictformat {
for _, pf := range formats {
if pf.Depth == depth && pf.Direct == direct {
return pf.Id
}
}
return 0
}
func main() {
X, err := xgb.NewConn()
if err != nil {
@@ -37,7 +54,7 @@ func main() {
visual, xproto.CwBackPixel|xproto.CwEventMask,
[]uint32{0xffffffff, xproto.EventMaskButtonPress |
xproto.EventMaskButtonMotion | xproto.EventMaskButtonRelease |
xproto.EventMaskStructureNotify})
xproto.EventMaskStructureNotify | xproto.EventMaskExposure})
title := []byte("Draw")
_ = xproto.ChangeProperty(X, xproto.PropModeReplace, wid, xproto.AtomWmName,
@@ -50,7 +67,8 @@ func main() {
log.Fatalln(err)
}
var pformat render.Pictformat
// Find appropriate picture formats.
var pformat, pformatAlpha, pformatRGB render.Pictformat
for _, pd := range pformats.Screens[X.DefaultScreen].Depths {
for _, pv := range pd.Visuals {
if pv.Visual == visual {
@@ -58,7 +76,26 @@ func main() {
}
}
}
if pformatAlpha = findPictureFormat(pformats.Formats, 8,
render.Directformat{
AlphaShift: 0,
AlphaMask: 0xff,
}); pformat == 0 {
log.Fatalln("required picture format not found")
}
if pformatRGB = findPictureFormat(pformats.Formats, 24,
render.Directformat{
RedShift: 16,
RedMask: 0xff,
GreenShift: 8,
GreenMask: 0xff,
BlueShift: 0,
BlueMask: 0xff,
}); pformatRGB == 0 {
log.Fatalln("required picture format not found")
}
// Picture for the window.
pid, err := render.NewPictureId(X)
if err != nil {
log.Fatalln(err)
@@ -66,6 +103,8 @@ func main() {
render.CreatePicture(X, pid, xproto.Drawable(wid), pformat, 0, []uint32{})
// Brush shape.
const brushRadius = 5
brushid, err := render.NewPictureId(X)
if err != nil {
log.Fatalln(err)
@@ -74,12 +113,12 @@ func main() {
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)},
render.Pointfix{F64ToFixed(brushRadius), F64ToFixed(brushRadius)},
render.Pointfix{F64ToFixed(brushRadius), F64ToFixed(brushRadius)},
F64ToFixed(0),
F64ToFixed(50),
2, []render.Fixed{F64ToFixed(0), F64ToFixed(1)},
[]render.Color{cFull, cTrans})
F64ToFixed(brushRadius),
3, []render.Fixed{F64ToFixed(0), F64ToFixed(0.1), F64ToFixed(1)},
[]render.Color{cFull, cFull, cTrans})
// Brush color.
colorid, err := render.NewPictureId(X)
@@ -87,22 +126,81 @@ func main() {
log.Fatalln(err)
}
_ = render.CreateSolidFill(X, colorid, render.Color{
Red: 0xcccc,
Green: 0xaaaa,
Blue: 0x8888,
Red: 0xeeee,
Green: 0x8888,
Blue: 0x4444,
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.
// Pixmaps.
const (
pixWidth = 1000
pixHeight = 1000
)
pixid, err := xproto.NewPixmapId(X)
if err != nil {
log.Fatalln(err)
}
_ = xproto.CreatePixmap(X, 24, pixid, xproto.Drawable(screen.Root),
pixWidth, pixHeight)
pixpictid, err := render.NewPictureId(X)
if err != nil {
log.Fatalln(err)
}
render.CreatePicture(X, pixpictid, xproto.Drawable(pixid),
pformatRGB, 0, []uint32{})
pixmaskid, err := xproto.NewPixmapId(X)
if err != nil {
log.Fatalln(err)
}
_ = xproto.CreatePixmap(X, 8, pixmaskid, xproto.Drawable(screen.Root),
pixWidth, pixHeight)
pixmaskpictid, err := render.NewPictureId(X)
if err != nil {
log.Fatalln(err)
}
render.CreatePicture(X, pixmaskpictid, xproto.Drawable(pixmaskid),
pformatAlpha, 0, []uint32{})
// Pixmaps come uninitialized.
render.FillRectangles(X,
render.PictOpSrc, pixpictid, render.Color{
Red: 0xffff, Green: 0xffff, Blue: 0xffff, Alpha: 0xffff,
}, []xproto.Rectangle{{Width: pixWidth, Height: pixHeight}})
// This is the only method we can use to render proper brush strokes.
//
// https://www.cairographics.org/operators/
// http://ssp.impulsetrain.com/porterduff.html
printAt := func(x, y int16) {
// ConjointOver is defined as: A = Aa * 1 + Ab * max(1-Aa/Ab,0)
// which basically resolves to: A = max(Aa, Ab)
// which equals "lighten" with one channel only.
//
// Resources:
// - https://www.cairographics.org/operators/
// - http://ssp.impulsetrain.com/porterduff.html
// - https://keithp.com/~keithp/talks/renderproblems/renderproblems/render-title.html
// - https://keithp.com/~keithp/talks/cairo2003.pdf
drawLineTo := func(x, y int16) {
_ = render.Composite(X, render.PictOpConjointOver,
brushid, render.PictureNone, pixmaskpictid,
0, 0, 0, 0, x-brushRadius, y-brushRadius,
brushRadius*2, brushRadius*2)
_ = render.SetPictureClipRectangles(X, pid,
x-brushRadius, y-brushRadius, []xproto.Rectangle{
{Width: brushRadius * 2, Height: brushRadius * 2}})
_ = render.Composite(X, render.PictOpSrc,
pixpictid, render.PictureNone, pid,
0, 0, 0, 0, 0 /* dst-x */, 0, /* dst-y */
pixWidth, pixHeight)
_ = render.Composite(X, render.PictOpOver,
colorid, brushid, pid,
0, 0, 0, 0, x-50, y-50, 100, 100)
colorid, pixmaskpictid, pid,
0, 0, 0, 0, 0 /* dst-x */, 0, /* dst-y */
pixWidth, pixHeight)
}
drawing := false
@@ -121,19 +219,44 @@ func main() {
case xproto.UnmapNotifyEvent:
return
case xproto.ExposeEvent:
_ = render.SetPictureClipRectangles(X, pid, int16(e.X), int16(e.Y),
[]xproto.Rectangle{{Width: e.Width, Height: e.Height}})
_ = render.Composite(X, render.PictOpSrc,
pixpictid, render.PictureNone, pid,
0, 0, 0, 0, 0 /* dst-x */, 0, /* dst-y */
pixWidth, pixHeight)
if drawing {
_ = render.Composite(X, render.PictOpOver,
colorid, pixmaskpictid, pid,
0, 0, 0, 0, 0 /* dst-x */, 0, /* dst-y */
pixWidth, pixHeight)
}
case xproto.ButtonPressEvent:
if e.Detail == xproto.ButtonIndex1 {
render.FillRectangles(X,
render.PictOpSrc, pixmaskpictid, render.Color{},
[]xproto.Rectangle{{Width: pixWidth, Height: pixHeight}})
drawing = true
printAt(e.EventX, e.EventY)
drawLineTo(e.EventX, e.EventY)
}
case xproto.MotionNotifyEvent:
if drawing {
printAt(e.EventX, e.EventY)
drawLineTo(e.EventX, e.EventY)
}
case xproto.ButtonReleaseEvent:
if e.Detail == xproto.ButtonIndex1 {
_ = render.Composite(X, render.PictOpOver,
colorid, pixmaskpictid, pixpictid,
0, 0, 0, 0, 0 /* dst-x */, 0, /* dst-y */
pixWidth, pixHeight)
drawing = false
}
}