Fix bound calculation with just emojis (again, super hacky)

draw2dimg/ftgc.go

@@ -275,10 +275,35 @@ func (gc *GraphicContext) GetStringBounds(s string) (left, top, right, bottom fl
 	top, left, bottom, right = 10e6, 10e6, -10e6, -10e6
 	cursor := 0.0
 	prev, hasPrev := truetype.Index(0), false
+	// Get sample letter for approximated emoji calculations
+	const letter = 'M'
+	mindex := f.Index(letter)
+	mtop, mleft, mheight, mwidth := 10e6, 10e6, -10e6, -10e6
+	if err := gc.glyphBuf.Load(gc.Current.Font, fixed.Int26_6(gc.Current.Scale), mindex, font.HintingNone); err != nil {
+		log.Println(err)
+		return 0, 0, 0, 0
+	}
+	e0 := 0
+	for _, e1 := range gc.glyphBuf.Ends {
+		ps := gc.glyphBuf.Points[e0:e1]
+		for _, p := range ps {
+			x, y := pointToF64Point(p)
+			mtop = math.Min(mtop, y)
+			mheight = math.Max(mheight, y)
+			mleft = math.Min(mleft, x)
+			mwidth = math.Max(mwidth, x)
+		}
+	}
+	mtop *= 1.2
+	mwidth *= 1.55
+	mheight += math.Abs(mtop-mheight) * 0.2
+	// Actually iterate through the string
 	for fragment := range gc.Emojis.Iterate(s) {
 		if fragment.IsEmoji {
-			cursor += fUnitsToFloat64(fixed.Int26_6(gc.Current.Scale)) * 1.15
-			left = math.Min(left, cursor)
+			cursor += mwidth
+			top = math.Min(top, mtop)
+			bottom = math.Max(bottom, mheight)
+			left = math.Min(left, mleft)
 			right = math.Max(right, cursor)
 			continue
 		}