xgb-draw: double buffer, change color, cleanup

prototypes/xgb-draw.go

@@ -1,9 +1,6 @@
 // Network-friendly drawing application based on XRender.
 //
-// TODO
-//  - use double buffering to remove flicker
-//    (more pronounced over X11 forwarding)
-//  - maybe keep the pixmap as large as the window
+// TODO: Maybe keep the pixmap as large as the window.
 package main
 
 import (
@@ -26,6 +23,23 @@ func findPictureFormat(formats []render.Pictforminfo,
 	return 0
 }
 
+func createNewPicture(X *xgb.Conn, depth byte, drawable xproto.Drawable,
+	width uint16, height uint16, format render.Pictformat) render.Picture {
+	pixmapid, err := xproto.NewPixmapId(X)
+	if err != nil {
+		log.Fatalln(err)
+	}
+	_ = xproto.CreatePixmap(X, depth, pixmapid, drawable, width, height)
+
+	pictid, err := render.NewPictureId(X)
+	if err != nil {
+		log.Fatalln(err)
+	}
+	_ = render.CreatePicture(X, pictid, xproto.Drawable(pixmapid), format,
+		0, []uint32{})
+	return pictid
+}
+
 func main() {
 	X, err := xgb.NewConn()
 	if err != nil {
@@ -125,53 +139,44 @@ func main() {
 		log.Fatalln(err)
 	}
 	_ = render.CreateSolidFill(X, colorid, render.Color{
-		Red:   0xeeee,
+		Red:   0x4444,
 		Green: 0x8888,
-		Blue:  0x4444,
+		Blue:  0xffff,
 		Alpha: 0xffff,
 	})
 
-	// Pixmaps.
+	// Various 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)
+	canvasid := createNewPicture(X, 24,
+		xproto.Drawable(screen.Root), pixWidth, pixHeight, pformatRGB)
+	bufferid := createNewPicture(X, 24,
+		xproto.Drawable(screen.Root), pixWidth, pixHeight, pformatRGB)
+	maskid := createNewPicture(X, 8,
+		xproto.Drawable(screen.Root), pixWidth, pixHeight, pformatAlpha)
 
-	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{})
+	// Smoothing by way of blur, apparently a misguided idea.
+	/*
+		_ = render.SetPictureFilter(X, maskid,
+			uint16(len("convolution")), "convolution",
+			[]render.Fixed{F64ToFixed(3), F64ToFixed(3),
+				F64ToFixed(0), F64ToFixed(0.15), F64ToFixed(0),
+				F64ToFixed(0.15), F64ToFixed(0.40), F64ToFixed(0.15),
+				F64ToFixed(0), F64ToFixed(0.15), F64ToFixed(0)})
+	*/
 
 	// Pixmaps come uninitialized.
-	render.FillRectangles(X,
-		render.PictOpSrc, pixpictid, render.Color{
+	_ = render.FillRectangles(X,
+		render.PictOpSrc, canvasid, 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.
+	// This is the only method we can use to render brush strokes without
+	// alpha accumulation due to stamping. Though this also seems to be
+	// misguided. Keeping it here for educational purposes.
 	//
 	// ConjointOver is defined as: A = Aa * 1 + Ab * max(1-Aa/Ab,0)
 	// which basically resolves to: A = max(Aa, Ab)
@@ -184,20 +189,28 @@ func main() {
 	//  - https://keithp.com/~keithp/talks/cairo2003.pdf
 	drawPointAt := func(x, y int16) {
 		_ = render.Composite(X, render.PictOpConjointOver,
-			brushid, render.PictureNone, pixmaskpictid,
+			brushid, render.PictureNone, maskid,
 			0, 0, 0, 0, x-brushRadius, y-brushRadius,
 			brushRadius*2, brushRadius*2)
 
-		_ = render.SetPictureClipRectangles(X, pid,
+		_ = render.SetPictureClipRectangles(X, bufferid,
 			x-brushRadius, y-brushRadius, []xproto.Rectangle{
 				{Width: brushRadius * 2, Height: brushRadius * 2}})
-
 		_ = render.Composite(X, render.PictOpSrc,
-			pixpictid, render.PictureNone, pid,
+			canvasid, render.PictureNone, bufferid,
 			0, 0, 0, 0, 0 /* dst-x */, 0, /* dst-y */
 			pixWidth, pixHeight)
 		_ = render.Composite(X, render.PictOpOver,
-			colorid, pixmaskpictid, pid,
+			colorid, maskid, bufferid,
+			0, 0, 0, 0, 0 /* dst-x */, 0, /* dst-y */
+			pixWidth, pixHeight)
+
+		// Composited, now blit to window without flicker.
+		_ = render.SetPictureClipRectangles(X, pid,
+			x-brushRadius, y-brushRadius, []xproto.Rectangle{
+				{Width: brushRadius * 2, Height: brushRadius * 2}})
+		_ = render.Composite(X, render.PictOpSrc,
+			bufferid, render.PictureNone, pid,
 			0, 0, 0, 0, 0 /* dst-x */, 0, /* dst-y */
 			pixWidth, pixHeight)
 	}
@@ -271,14 +284,16 @@ func main() {
 			_ = render.SetPictureClipRectangles(X, pid, int16(e.X), int16(e.Y),
 				[]xproto.Rectangle{{Width: e.Width, Height: e.Height}})
 
+			// Not bothering to deflicker here using the buffer pixmap,
+			// with compositing this event is rare enough.
 			_ = render.Composite(X, render.PictOpSrc,
-				pixpictid, render.PictureNone, pid,
+				canvasid, 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,
+					colorid, maskid, pid,
 					0, 0, 0, 0, 0 /* dst-x */, 0, /* dst-y */
 					pixWidth, pixHeight)
 			}
@@ -286,7 +301,7 @@ func main() {
 		case xproto.ButtonPressEvent:
 			if e.Detail == xproto.ButtonIndex1 {
 				render.FillRectangles(X,
-					render.PictOpSrc, pixmaskpictid, render.Color{},
+					render.PictOpSrc, maskid, render.Color{},
 					[]xproto.Rectangle{{Width: pixWidth, Height: pixHeight}})
 
 				drawing = true
@@ -303,7 +318,7 @@ func main() {
 		case xproto.ButtonReleaseEvent:
 			if e.Detail == xproto.ButtonIndex1 {
 				_ = render.Composite(X, render.PictOpOver,
-					colorid, pixmaskpictid, pixpictid,
+					colorid, maskid, canvasid,
 					0, 0, 0, 0, 0 /* dst-x */, 0, /* dst-y */
 					pixWidth, pixHeight)