xgb-render: preliminary text rendering

I have finally got it working at all, now let's fix bounds etc.

prototypes/xgb-xrender.go

@@ -1,9 +1,16 @@
 package main
 
 import (
+	"fmt"
 	"github.com/BurntSushi/xgb"
 	"github.com/BurntSushi/xgb/render"
 	"github.com/BurntSushi/xgb/xproto"
+	"github.com/golang/freetype"
+	"github.com/golang/freetype/truetype"
+	"golang.org/x/image/font"
+	"golang.org/x/image/font/gofont/goregular"
+	"golang.org/x/image/math/fixed"
+	"image"
 	"log"
 	"math/rand"
 )
@@ -11,6 +18,98 @@ import (
 func F64ToFixed(f float64) render.Fixed { return render.Fixed(f * 65536) }
 func FixedToF64(f render.Fixed) float64 { return float64(f) / 65536 }
 
+func glyphListBytes(buf []byte, runes []rune, size int) int {
+	b := 0
+	for _, r := range runes {
+		switch size {
+		default:
+			buf[b] = byte(r)
+			b += 1
+		case 2:
+			xgb.Put16(buf[b:], uint16(r))
+			b += 2
+		case 4:
+			xgb.Put32(buf[b:], uint32(r))
+			b += 4
+		}
+	}
+	return xgb.Pad(b)
+}
+
+// When the len is 255, a GLYPHABLE follows, otherwise a list of CARD8/16/32.
+func glyphEltHeaderBytes(buf []byte, len byte, deltaX, deltaY int16) int {
+	b := 0
+	buf[b] = len
+	b += 4
+	xgb.Put16(buf[b:], uint16(deltaX))
+	b += 2
+	xgb.Put16(buf[b:], uint16(deltaY))
+	b += 2
+	return xgb.Pad(b)
+}
+
+type xgbCookie interface{ Check() error }
+
+// TODO: We actually need a higher-level function that also keeps track of
+// and loads glyphs into the X server.
+
+// compositeString makes an appropriate render.CompositeGlyphs request,
+// assuming that glyphs equal Unicode codepoints.
+func compositeString(c *xgb.Conn, op byte, src, dst render.Picture,
+	maskFormat render.Pictformat, glyphset render.Glyphset, srcX, srcY int16,
+	destX, destY int16, text string) xgbCookie {
+	runes := []rune(text)
+
+	var highest rune
+	for _, r := range runes {
+		if r > highest {
+			highest = r
+		}
+	}
+
+	size := 1
+	switch {
+	case highest > 1<<16:
+		size = 4
+	case highest > 1<<8:
+		size = 2
+	}
+
+	// They gave up on the XCB protocol API and we need to serialize explicitly.
+
+	// To spare us from caring about the padding, use the largest number lesser
+	// than 255 that is divisible by 4 (for size 2 and 4 the requirements are
+	// less strict but this works in the general case).
+	const maxPerChunk = 252
+
+	buf := make([]byte, (len(runes)+maxPerChunk-1)/maxPerChunk*8+len(runes)*size)
+	b := 0
+
+	for len(runes) > maxPerChunk {
+		b += glyphEltHeaderBytes(buf[b:], maxPerChunk, 0, 0)
+		b += glyphListBytes(buf[b:], runes[:maxPerChunk], size)
+		runes = runes[maxPerChunk:]
+	}
+	if len(runes) > 0 {
+		b += glyphEltHeaderBytes(buf[b:], byte(len(runes)), destX, destY)
+		b += glyphListBytes(buf[b:], runes, size)
+	}
+
+	switch size {
+	default:
+		return render.CompositeGlyphs8(c, op, src, dst, maskFormat, glyphset,
+			srcX, srcY, buf)
+	case 2:
+		return render.CompositeGlyphs16(c, op, src, dst, maskFormat, glyphset,
+			srcX, srcY, buf)
+	case 4:
+		return render.CompositeGlyphs32(c, op, src, dst, maskFormat, glyphset,
+			srcX, srcY, buf)
+	}
+}
+
+// ---
+
 func main() {
 	X, err := xgb.NewConn()
 	if err != nil {
@@ -119,6 +218,79 @@ func main() {
 	// ...or just scan through pformats.Formats and look for matches, which is
 	// what XRenderFindStandardFormat in Xlib does as well as exp/shiny.
 
+	f, err := freetype.ParseFont(goregular.TTF)
+	if err != nil {
+		log.Fatalln(err)
+	}
+
+	c := freetype.NewContext()
+	c.SetDPI(96) // TODO: Take this from the screen or monitor.
+	c.SetFont(f)
+	c.SetFontSize(9)
+	c.SetSrc(image.White)
+	c.SetHinting(font.HintingFull)
+	// TODO: Seems like we want to use NRGBA. Or RGBA if the A is always 1.
+	// Or implement our own image.Image for direct gamma-corrected RGB!
+	nrgb := image.NewRGBA(image.Rect(0, 0, 36, 36))
+	c.SetClip(nrgb.Bounds())
+	c.SetDst(nrgb)
+
+	bounds := f.Bounds(c.PointToFixed(9 /* FIXME: Duplication. */))
+	log.Println("+%v", bounds)
+
+	// FIXME: Duplication.
+	opts := truetype.Options{
+		Size: 9,
+		DPI:  96,
+	}
+
+	// TODO: Seems this satisfies the sfnt interface, DrawString just adds
+	// kerning and DrawMask on top.
+	face := truetype.NewFace(f, &opts)
+	_ = face
+
+	// TODO: Figure out a way to load glyphs into XRender.
+	var rgbFormat render.Pictformat
+	for _, pf := range pformats.Formats {
+		// Hopefully. Might want to check ARGB/BGRA.
+		if pf.Depth == 32 && pf.Direct.AlphaMask != 0 {
+			rgbFormat = pf.Id
+			log.Printf("%+v\n", pf)
+			break
+		}
+	}
+
+	gsid, err := render.NewGlyphsetId(X)
+	if err != nil {
+		log.Fatalln(err)
+	}
+
+	// NOTE: A depth of 24 will not work, the server always rejects it.
+	_ = render.CreateGlyphSet(X, gsid, rgbFormat)
+
+	for r := rune(32); r < 128; r++ {
+		for i := 0; i < len(nrgb.Pix); i++ {
+			nrgb.Pix[i] = 0
+		}
+
+		advance, err := c.DrawString(string(r), fixed.P(18, 18))
+		_, _ = advance, err
+		if err != nil {
+			log.Println("skip")
+			continue
+		}
+
+		_ = render.AddGlyphs(X, gsid, 1, []uint32{uint32(r)},
+			[]render.Glyphinfo{{
+				Width:  uint16(36),
+				Height: uint16(36),
+				X:      int16(18),
+				Y:      int16(18),
+				XOff:   int16(18),
+				YOff:   0,
+			}}, []byte(nrgb.Pix))
+	}
+
 	pid, err := render.NewPictureId(X)
 	if err != nil {
 		log.Fatalln(err)
@@ -133,9 +305,22 @@ func main() {
 		log.Fatalln(err)
 	}
 
+	whiteid, err := render.NewPictureId(X)
+	if err != nil {
+		log.Fatalln(err)
+	}
+
+	_ = render.CreateSolidFill(X, whiteid, render.Color{
+		Red:   0xffff,
+		Green: 0xffff,
+		Blue:  0xffff,
+		Alpha: 0xffff,
+	})
+
 	var from, to render.Color
+	var start, end uint32
 	recolor := func() {
-		start := rand.Uint32() & 0xffffff
+		start = rand.Uint32() & 0xffffff
 		from = render.Color{
 			Red:   0x101 * uint16((start>>16)&0xff),
 			Green: 0x101 * uint16((start>>8)&0xff),
@@ -143,7 +328,7 @@ func main() {
 			Alpha: 0xffff,
 		}
 
-		end := rand.Uint32() & 0xffffff
+		end = rand.Uint32() & 0xffffff
 		to = render.Color{
 			Red:   0x101 * uint16((end>>16)&0xff),
 			Green: 0x101 * uint16((end>>8)&0xff),
@@ -169,6 +354,10 @@ func main() {
 			0, 0, 0, 0, 50, 50, w-100, h-100)
 
 		_ = render.FreePicture(X, gid)
+
+		_ = compositeString(X, render.PictOpOver, whiteid, pid,
+			0 /* TODO: mask Pictureformat? */, gsid, 0, 0, 100, 100,
+			fmt.Sprintf("%#06x - %#06x", start, end))
 	}
 
 	for {