xgb-draw: proper brush stroke render
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df082e1dee
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254ceb810c
GPG Key ID:
A0420B94F92B9493
@ -1,3 +1,10 @@
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// Network-friendly drawing application based on XRender.
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//
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// TODO
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// - interpolate motion between points
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// - use double buffering to remove flicker
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// (more pronounced over X11 forwarding)
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// - maybe keep the pixmap as large as the window
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package main
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import (
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@ -10,6 +17,16 @@ import (
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func F64ToFixed(f float64) render.Fixed { return render.Fixed(f * 65536) }
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func FixedToF64(f render.Fixed) float64 { return float64(f) / 65536 }
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func findPictureFormat(formats []render.Pictforminfo,
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depth byte, direct render.Directformat) render.Pictformat {
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for _, pf := range formats {
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if pf.Depth == depth && pf.Direct == direct {
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return pf.Id
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}
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}
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return 0
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}
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func main() {
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X, err := xgb.NewConn()
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if err != nil {
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@ -37,7 +54,7 @@ func main() {
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visual, xproto.CwBackPixel|xproto.CwEventMask,
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[]uint32{0xffffffff, xproto.EventMaskButtonPress |
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xproto.EventMaskButtonMotion | xproto.EventMaskButtonRelease |
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xproto.EventMaskStructureNotify})
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xproto.EventMaskStructureNotify | xproto.EventMaskExposure})
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title := []byte("Draw")
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_ = xproto.ChangeProperty(X, xproto.PropModeReplace, wid, xproto.AtomWmName,
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@ -50,7 +67,8 @@ func main() {
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log.Fatalln(err)
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}
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var pformat render.Pictformat
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// Find appropriate picture formats.
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var pformat, pformatAlpha, pformatRGB render.Pictformat
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for _, pd := range pformats.Screens[X.DefaultScreen].Depths {
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for _, pv := range pd.Visuals {
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if pv.Visual == visual {
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@ -58,7 +76,26 @@ func main() {
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}
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}
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}
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if pformatAlpha = findPictureFormat(pformats.Formats, 8,
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render.Directformat{
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AlphaShift: 0,
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AlphaMask: 0xff,
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}); pformat == 0 {
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log.Fatalln("required picture format not found")
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}
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if pformatRGB = findPictureFormat(pformats.Formats, 24,
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render.Directformat{
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RedShift: 16,
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RedMask: 0xff,
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GreenShift: 8,
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GreenMask: 0xff,
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BlueShift: 0,
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BlueMask: 0xff,
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}); pformatRGB == 0 {
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log.Fatalln("required picture format not found")
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}
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// Picture for the window.
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pid, err := render.NewPictureId(X)
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if err != nil {
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log.Fatalln(err)
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@ -66,6 +103,8 @@ func main() {
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render.CreatePicture(X, pid, xproto.Drawable(wid), pformat, 0, []uint32{})
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// Brush shape.
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const brushRadius = 5
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brushid, err := render.NewPictureId(X)
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if err != nil {
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log.Fatalln(err)
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@ -74,12 +113,12 @@ func main() {
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cFull := render.Color{0xffff, 0xffff, 0xffff, 0xffff}
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cTrans := render.Color{0xffff, 0xffff, 0xffff, 0}
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_ = render.CreateRadialGradient(X, brushid,
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render.Pointfix{F64ToFixed(50), F64ToFixed(50)},
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render.Pointfix{F64ToFixed(50), F64ToFixed(50)},
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render.Pointfix{F64ToFixed(brushRadius), F64ToFixed(brushRadius)},
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render.Pointfix{F64ToFixed(brushRadius), F64ToFixed(brushRadius)},
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F64ToFixed(0),
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F64ToFixed(50),
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2, []render.Fixed{F64ToFixed(0), F64ToFixed(1)},
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[]render.Color{cFull, cTrans})
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F64ToFixed(brushRadius),
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3, []render.Fixed{F64ToFixed(0), F64ToFixed(0.1), F64ToFixed(1)},
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[]render.Color{cFull, cFull, cTrans})
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// Brush color.
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colorid, err := render.NewPictureId(X)
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@ -87,22 +126,81 @@ func main() {
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log.Fatalln(err)
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}
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_ = render.CreateSolidFill(X, colorid, render.Color{
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Red: 0xcccc,
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Green: 0xaaaa,
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Blue: 0x8888,
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Red: 0xeeee,
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Green: 0x8888,
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Blue: 0x4444,
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Alpha: 0xffff,
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})
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// Unfortunately, XRender won't give us any /blending operators/, only
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// providing basic Porter-Duff ones with useless disjoint/conjoint variants,
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// but we need the "lighten" operator to draw brush strokes properly.
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// Pixmaps.
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const (
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pixWidth = 1000
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pixHeight = 1000
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)
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pixid, err := xproto.NewPixmapId(X)
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if err != nil {
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log.Fatalln(err)
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}
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_ = xproto.CreatePixmap(X, 24, pixid, xproto.Drawable(screen.Root),
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pixWidth, pixHeight)
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pixpictid, err := render.NewPictureId(X)
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if err != nil {
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log.Fatalln(err)
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}
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render.CreatePicture(X, pixpictid, xproto.Drawable(pixid),
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pformatRGB, 0, []uint32{})
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pixmaskid, err := xproto.NewPixmapId(X)
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if err != nil {
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log.Fatalln(err)
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}
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_ = xproto.CreatePixmap(X, 8, pixmaskid, xproto.Drawable(screen.Root),
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pixWidth, pixHeight)
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pixmaskpictid, err := render.NewPictureId(X)
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if err != nil {
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log.Fatalln(err)
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}
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render.CreatePicture(X, pixmaskpictid, xproto.Drawable(pixmaskid),
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pformatAlpha, 0, []uint32{})
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// Pixmaps come uninitialized.
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render.FillRectangles(X,
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render.PictOpSrc, pixpictid, render.Color{
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Red: 0xffff, Green: 0xffff, Blue: 0xffff, Alpha: 0xffff,
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}, []xproto.Rectangle{{Width: pixWidth, Height: pixHeight}})
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// This is the only method we can use to render proper brush strokes.
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//
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// https://www.cairographics.org/operators/
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// http://ssp.impulsetrain.com/porterduff.html
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printAt := func(x, y int16) {
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// ConjointOver is defined as: A = Aa * 1 + Ab * max(1-Aa/Ab,0)
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// which basically resolves to: A = max(Aa, Ab)
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// which equals "lighten" with one channel only.
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//
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// Resources:
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// - https://www.cairographics.org/operators/
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// - http://ssp.impulsetrain.com/porterduff.html
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// - https://keithp.com/~keithp/talks/renderproblems/renderproblems/render-title.html
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// - https://keithp.com/~keithp/talks/cairo2003.pdf
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drawLineTo := func(x, y int16) {
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_ = render.Composite(X, render.PictOpConjointOver,
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brushid, render.PictureNone, pixmaskpictid,
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0, 0, 0, 0, x-brushRadius, y-brushRadius,
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brushRadius*2, brushRadius*2)
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_ = render.SetPictureClipRectangles(X, pid,
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x-brushRadius, y-brushRadius, []xproto.Rectangle{
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{Width: brushRadius * 2, Height: brushRadius * 2}})
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_ = render.Composite(X, render.PictOpSrc,
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pixpictid, render.PictureNone, pid,
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0, 0, 0, 0, 0 /* dst-x */, 0, /* dst-y */
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pixWidth, pixHeight)
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_ = render.Composite(X, render.PictOpOver,
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colorid, brushid, pid,
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0, 0, 0, 0, x-50, y-50, 100, 100)
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colorid, pixmaskpictid, pid,
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0, 0, 0, 0, 0 /* dst-x */, 0, /* dst-y */
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pixWidth, pixHeight)
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}
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drawing := false
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@ -121,19 +219,44 @@ func main() {
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case xproto.UnmapNotifyEvent:
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return
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case xproto.ExposeEvent:
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_ = render.SetPictureClipRectangles(X, pid, int16(e.X), int16(e.Y),
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[]xproto.Rectangle{{Width: e.Width, Height: e.Height}})
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_ = render.Composite(X, render.PictOpSrc,
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pixpictid, render.PictureNone, pid,
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0, 0, 0, 0, 0 /* dst-x */, 0, /* dst-y */
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pixWidth, pixHeight)
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if drawing {
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_ = render.Composite(X, render.PictOpOver,
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colorid, pixmaskpictid, pid,
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0, 0, 0, 0, 0 /* dst-x */, 0, /* dst-y */
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pixWidth, pixHeight)
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}
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case xproto.ButtonPressEvent:
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if e.Detail == xproto.ButtonIndex1 {
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render.FillRectangles(X,
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render.PictOpSrc, pixmaskpictid, render.Color{},
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[]xproto.Rectangle{{Width: pixWidth, Height: pixHeight}})
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drawing = true
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printAt(e.EventX, e.EventY)
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drawLineTo(e.EventX, e.EventY)
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}
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case xproto.MotionNotifyEvent:
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if drawing {
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printAt(e.EventX, e.EventY)
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drawLineTo(e.EventX, e.EventY)
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}
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case xproto.ButtonReleaseEvent:
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if e.Detail == xproto.ButtonIndex1 {
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_ = render.Composite(X, render.PictOpOver,
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colorid, pixmaskpictid, pixpictid,
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0, 0, 0, 0, 0 /* dst-x */, 0, /* dst-y */
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pixWidth, pixHeight)
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drawing = false
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}
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}
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