Fix font baseline issue

textfield.go

@@ -86,6 +86,9 @@ type TextField struct {
 	// overrideLineHeight is the custom height for a line of text, or 0 to disable.
 	overrideLineHeight int
 
+	// lineOffset is the offset of the baseline current font.
+	lineOffset int
+
 	// textColor is the color of the text within the field.
 	textColor color.Color
 
@@ -151,7 +154,7 @@ func NewTextField(face font.Face) *TextField {
 		scrollAutoHide:  true,
 		visible:         true,
 	}
-	f.setDefaultLineHeight()
+	f.fontUpdated()
 	return f
 }
 
@@ -298,7 +301,7 @@ func (f *TextField) SetFont(face font.Face) {
 	defer f.Unlock()
 
 	f.face = face
-	f.setDefaultLineHeight()
+	f.fontUpdated()
 }
 
 // Padding returns the amount of padding around the text within the field.
@@ -510,9 +513,10 @@ func (f *TextField) Draw(screen *ebiten.Image) {
 	screen.DrawImage(f.img, op)
 }
 
-func (f *TextField) setDefaultLineHeight() {
-	lineBounds := text.BoundString(f.face, "ATZgpq.")
-	f.lineHeight = lineBounds.Dy() + 5
+func (f *TextField) fontUpdated() {
+	m := f.face.Metrics()
+	f.lineHeight = m.Height.Round()
+	f.lineOffset = m.Ascent.Round()
 }
 
 func (f *TextField) wrapContent(withScrollBar bool) {
@@ -542,6 +546,7 @@ func (f *TextField) wrapContent(withScrollBar bool) {
 		}
 
 		l := len(line)
+		availableWidth := w - (f.padding * 2)
 		var start int
 		var end int
 		var initialEnd int
@@ -550,29 +555,29 @@ func (f *TextField) wrapContent(withScrollBar bool) {
 				initialEnd = end
 
 				bounds := text.BoundString(f.face, line[start:end])
-				if bounds.Dx() <= w-(f.padding*2) {
-					if f.wordWrap {
-						if end < l && !unicode.IsSpace(rune(line[end])) {
-							for endOffset := 0; endOffset < end-start; endOffset++ {
-								if unicode.IsSpace(rune(line[end-endOffset])) {
-									end = end - endOffset
-									if end < l-1 {
-										end++
-									}
-									break
-								}
+				if bounds.Dx() > availableWidth {
+					continue
+				}
+
+				if f.wordWrap && end < l && !unicode.IsSpace(rune(line[end])) {
+					for endOffset := 0; endOffset < end-start; endOffset++ {
+						if unicode.IsSpace(rune(line[end-endOffset])) {
+							end = end - endOffset
+							if end < l-1 {
+								end++
 							}
+							break
 						}
 					}
-
-					if end != initialEnd && f.horizontal != AlignStart {
-						bounds = text.BoundString(f.face, line[start:end])
-					}
-
-					f.bufferWrapped = append(f.bufferWrapped, line[start:end])
-					f.lineWidths = append(f.lineWidths, bounds.Dx())
-					break
 				}
+
+				if end != initialEnd && f.horizontal != AlignStart {
+					bounds = text.BoundString(f.face, line[start:end])
+				}
+
+				f.bufferWrapped = append(f.bufferWrapped, line[start:end])
+				f.lineWidths = append(f.lineWidths, bounds.Dx())
+				break
 			}
 			start = end
 		}
@@ -595,22 +600,23 @@ func (f *TextField) drawContent() (overflow bool) {
 	if lineHeight == 0 {
 		lineHeight = f.lineHeight
 	}
-	lineOffset := lineHeight / 3
+
 	f.bufferSize = 0
 	for i, line := range f.bufferWrapped {
 		lineX := f.padding
-		lineY := f.padding
-
-		lineY += lineHeight*(i+1) - lineOffset
+		lineY := f.lineOffset + lineHeight*i
 
+		// Calculate buffer size (width or height).
 		if f.singleLine {
 			bounds := text.BoundString(f.face, line)
-			f.bufferSize = bounds.Dx() + f.padding*4
+			f.bufferSize = bounds.Dx() + f.padding*2
 		} else {
-			f.bufferSize = lineY + lineOffset + f.padding
+			f.bufferSize = lineY + f.padding*2
 		}
 
-		if lineY < 0 || lineY >= h-(f.padding*2) {
+		// Calculate whether the line overflows the visible area.
+		lineOverflows := lineY < 0 || lineY >= h-(f.padding*2)
+		if lineOverflows {
 			overflow = true
 		}
 
@@ -619,24 +625,28 @@ func (f *TextField) drawContent() (overflow bool) {
 			continue
 		}
 
+		// Apply scrolling transformation.
 		if f.singleLine {
 			lineX -= f.offset
 		} else {
 			lineY -= f.offset
 		}
 
+		// Align horizontally.
 		if f.horizontal == AlignCenter {
 			lineX = (fieldWidth - f.lineWidths[i]) / 2
 		} else if f.horizontal == AlignEnd {
 			lineX = (fieldWidth - f.lineWidths[i]) - f.padding*2
 		}
 
+		// Align vertically.
 		if f.vertical == AlignCenter && lineHeight*lines <= h {
-			lineY = (fieldHeight-(lineHeight*lines))/2 + lineHeight*(i+1) - lineOffset
+			lineY = (fieldHeight-(lineHeight*lines))/2 + lineHeight*(i+1) - f.lineOffset
 		} else if f.vertical == AlignEnd && lineHeight*lines <= h {
 			lineY = (fieldHeight - lineHeight*i) - f.padding*2
 		}
 
+		// Draw line.
 		text.Draw(f.img, line, f.face, lineX, lineY, f.textColor)
 	}