bitmap.go

package textrender

import (
	"image"
	"image/color"
	"image/png"
	"io"

	"golang.org/x/image/font"
	"golang.org/x/image/font/basicfont"
	"golang.org/x/image/math/fixed"
)

// BitmapRenderer renders text layout as a bitmap image
type BitmapRenderer struct {
	FontFace   font.Face   // Font to use for rendering
	Background color.Color // Background color
	TextColor  color.Color // Text color
	Padding    int         // Padding around text in pixels
}

// DefaultBitmapRenderer returns a renderer with default settings
func DefaultBitmapRenderer() *BitmapRenderer {
	return &BitmapRenderer{
		FontFace:   basicfont.Face7x13,
		Background: color.White,
		TextColor:  color.Black,
		Padding:    10,
	}
}

// Render renders the text layout as a PNG image
func (r *BitmapRenderer) Render(layout *TextLayout) image.Image {
	if r.FontFace == nil {
		r.FontFace = basicfont.Face7x13
	}
	if r.Background == nil {
		r.Background = color.White
	}
	if r.TextColor == nil {
		r.TextColor = color.Black
	}

	// Calculate image dimensions
	bounds := r.FontFace.Metrics().Height
	lineHeight := bounds.Ceil()

	// For fixed-width fonts, calculate character width
	advance, _ := r.FontFace.GlyphAdvance('M')
	charWidth := advance.Ceil()

	numLines := len(layout.Lines)
	width := layout.Options.Width*charWidth + 2*r.Padding
	height := numLines*lineHeight + 2*r.Padding

	// Create image
	img := image.NewRGBA(image.Rect(0, 0, width, height))

	// Fill background
	for y := 0; y < height; y++ {
		for x := 0; x < width; x++ {
			img.Set(x, y, r.Background)
		}
	}

	// Create drawer
	drawer := &font.Drawer{
		Dst:  img,
		Src:  image.NewUniform(r.TextColor),
		Face: r.FontFace,
	}

	// Draw each line
	ascent := r.FontFace.Metrics().Ascent.Ceil()
	for i, line := range layout.Lines {
		y := r.Padding + ascent + i*lineHeight
		drawer.Dot = fixed.P(r.Padding, y)
		drawer.DrawString(line)
	}

	return img
}

// RenderToPNG renders the text layout and writes it as PNG to the writer
func (r *BitmapRenderer) RenderToPNG(layout *TextLayout, w io.Writer) error {
	img := r.Render(layout)
	return png.Encode(w, img)
}

// RenderBitmap is a convenience function to render text as a bitmap image
func RenderBitmap(text string, options LayoutOptions) image.Image {
	layout := Layout(text, options)
	renderer := DefaultBitmapRenderer()
	return renderer.Render(layout)
}