package canvas // Text rendering functions using the HTML 5 canvas. import ( "fmt" "path/filepath" "strings" "git.kirsle.net/go/render" ) // FontFilenameToName converts a FontFilename to its CSS font name. // // The CSS font name is set to the base of the filename, without the .ttf // file extension. For example, "fonts/DejaVuSans.ttf" uses the CSS font // family name "DejaVuSans" and that's what this function returns. // // Fonts must be defined in the index.html style sheet when serving the // wasm build of Doodle. // // If filename is "", returns "serif" as a sensible default. func FontFilenameToName(filename string) string { if filename == "" { return "DejaVuSans,serif" } return strings.TrimSuffix(filepath.Base(filename), filepath.Ext(filename)) } // DrawText draws text on the canvas. func (e *Engine) DrawText(text render.Text, point render.Point) error { font := FontFilenameToName(text.FontFilename) e.canvas.ctx2d.Set("font", fmt.Sprintf("%dpx %s,serif", text.Size, font), ) e.canvas.ctx2d.Set("textBaseline", "top") write := func(dx, dy int, color render.Color) { e.canvas.ctx2d.Set("fillStyle", color.ToHex()) e.canvas.ctx2d.Call("fillText", text.Text, int(point.X)+dx, int(point.Y)+dy, ) } // Does the text have a stroke around it? if text.Stroke != render.Invisible { e.canvas.ctx2d.Set("fillStyle", text.Stroke.ToHex()) write(-1, -1, text.Stroke) write(-1, 0, text.Stroke) write(-1, 1, text.Stroke) write(1, -1, text.Stroke) write(1, 0, text.Stroke) write(1, 1, text.Stroke) write(0, -1, text.Stroke) write(0, 1, text.Stroke) } // Does it have a drop shadow? if text.Shadow != render.Invisible { write(1, 1, text.Shadow) } // Draw the text itself. write(0, 0, text.Color) return nil } // ComputeTextRect computes and returns a Rect for how large the text would // appear if rendered. func (e *Engine) ComputeTextRect(text render.Text) (render.Rect, error) { font := FontFilenameToName(text.FontFilename) e.canvas.ctx2d.Set("font", fmt.Sprintf("%dpx %s,serif", text.Size, font), ) measure := e.canvas.ctx2d.Call("measureText", text.Text) rect := render.Rect{ // TODO: the only TextMetrics widely supported in browsers is // the width. For height, use the text size for now. W: measure.Get("width").Int(), H: text.Size, } return rect, nil }