89 lines
2.3 KiB
Go
89 lines
2.3 KiB
Go
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package canvas
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// Text rendering functions using the HTML 5 canvas.
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import (
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"fmt"
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"path/filepath"
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"strings"
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"git.kirsle.net/apps/doodle/lib/render"
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)
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// FontFilenameToName converts a FontFilename to its CSS font name.
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//
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// The CSS font name is set to the base of the filename, without the .ttf
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// file extension. For example, "fonts/DejaVuSans.ttf" uses the CSS font
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// family name "DejaVuSans" and that's what this function returns.
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//
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// Fonts must be defined in the index.html style sheet when serving the
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// wasm build of Doodle.
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//
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// If filename is "", returns "serif" as a sensible default.
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func FontFilenameToName(filename string) string {
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if filename == "" {
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return "DejaVuSans,serif"
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}
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return strings.TrimSuffix(filepath.Base(filename), filepath.Ext(filename))
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}
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// DrawText draws text on the canvas.
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func (e *Engine) DrawText(text render.Text, point render.Point) error {
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font := FontFilenameToName(text.FontFilename)
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e.canvas.ctx2d.Set("font",
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fmt.Sprintf("%dpx %s,serif", text.Size, font),
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)
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e.canvas.ctx2d.Set("textBaseline", "top")
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write := func(dx, dy int, color render.Color) {
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e.canvas.ctx2d.Set("fillStyle", color.ToHex())
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e.canvas.ctx2d.Call("fillText",
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text.Text,
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int(point.X)+dx,
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int(point.Y)+dy,
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)
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}
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// Does the text have a stroke around it?
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if text.Stroke != render.Invisible {
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e.canvas.ctx2d.Set("fillStyle", text.Stroke.ToHex())
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write(-1, -1, text.Stroke)
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write(-1, 0, text.Stroke)
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write(-1, 1, text.Stroke)
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write(1, -1, text.Stroke)
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write(1, 0, text.Stroke)
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write(1, 1, text.Stroke)
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write(0, -1, text.Stroke)
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write(0, 1, text.Stroke)
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}
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// Does it have a drop shadow?
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if text.Shadow != render.Invisible {
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write(1, 1, text.Shadow)
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}
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// Draw the text itself.
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write(0, 0, text.Color)
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return nil
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}
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// ComputeTextRect computes and returns a Rect for how large the text would
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// appear if rendered.
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func (e *Engine) ComputeTextRect(text render.Text) (render.Rect, error) {
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font := FontFilenameToName(text.FontFilename)
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e.canvas.ctx2d.Set("font",
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fmt.Sprintf("%dpx %s,serif", text.Size, font),
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)
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measure := e.canvas.ctx2d.Call("measureText", text.Text)
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rect := render.Rect{
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// TODO: the only TextMetrics widely supported in browsers is
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// the width. For height, use the text size for now.
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W: int32(measure.Get("width").Int()),
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H: int32(text.Size),
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}
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return rect, nil
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}
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