wailsapp/wails · error

Invalid font style

Error message

Invalid font style

What it means

NewFont validates the style bitmask before creating the font: style must be a subset of FontBold|FontItalic|FontUnderline|FontStrikeOut (values 1|2|4|8 = 0x0F). Any style byte with bits above 0x0F — including accidentally passing a point size, a color, or a style enum from a different API — panics with 'Invalid font style'. This is a pure argument-validation panic, not a Win32 failure.

Source

Thrown at v2/internal/frontend/desktop/windows/winc/font.go:36

	FontItalic    byte = 0x02
	FontUnderline byte = 0x04
	FontStrikeOut byte = 0x08
)

func init() {
	DefaultFont = NewFont("MS Shell Dlg 2", 8, 0)
}

type Font struct {
	hfont     w32.HFONT
	family    string
	pointSize int
	style     byte
}

func NewFont(family string, pointSize int, style byte) *Font {
	if style > FontBold|FontItalic|FontUnderline|FontStrikeOut {
		panic("Invalid font style")
	}

	//Retrive screen DPI
	hDC := w32.GetDC(0)
	defer w32.ReleaseDC(0, hDC)
	screenDPIY := w32.GetDeviceCaps(hDC, w32.LOGPIXELSY)

	font := Font{
		family:    family,
		pointSize: pointSize,
		style:     style,
	}

	font.hfont = font.createForDPI(screenDPIY)
	if font.hfont == 0 {
		panic("CreateFontIndirect failed")
	}

View on GitHub (pinned to 0e754b1b40)

Solutions

1. Build the style only from winc constants: winc.FontBold, winc.FontItalic, winc.FontUnderline, winc.FontStrikeOut (OR them together)
2. Mask the style defensively before the call: style & (FontBold|FontItalic|FontUnderline|FontStrikeOut)
3. Double-check the NewFont signature (family string, pointSize int, style byte) when porting code

Example fix

// before
fnt := winc.NewFont("Segoe UI", 9, 12) // 12 = 0b1100 -> only underline(4)+strikeout(8) bits, ok; but 16+ panics
fnt := winc.NewFont("Segoe UI", 9, winc.FontBold|16) // invalid bit -> panic

// after
fnt := winc.NewFont("Segoe UI", 9, winc.FontBold|winc.FontItalic) // subset of 0x0F

const fontStyleMask = winc.FontBold | winc.FontItalic | winc.FontUnderline | winc.FontStrikeOut // 0x0F

func safeStyle(s byte) byte { return s & fontStyleMask }

fnt := winc.NewFont("Segoe UI", 9, safeStyle(incomingStyle))

When it happens

Trigger: Calling winc.NewFont(family, size, style) with style > 0x0F, e.g. NewFont("Segoe UI", 9, 16); mixing up parameter order so a size lands in the style slot; OR-ing in a custom flag not defined by winc.

Common situations: Porting font code from other toolkits whose style enums use different bit values; copy-paste parameter-order mistakes (family/pointSize/style swapped).

Related errors

• GetSysColorBrush failed
• Cannot create canvas from invalid HDC.
• CreateFontIndirect failed
• Faild to create solid color brush
• Failed to create null brush

AI-assisted analysis of wailsapp/wails@0e754b1b40 (2026-08-15). Data as JSON: /api/errors/e5e37715fd753a68. Report an issue: GitHub.