typeset/draw.go

package typeset

import "image"
import "unicode"
import "image/draw"
import "image/color"
import "golang.org/x/image/font"
import "golang.org/x/image/math/fixed"
import "git.tebibyte.media/tomo/typeset/internal"

// Draw draws the contents of a TypeSetter to an image at the given offset. It
// returns a rectangle containing all pixels in the image that were updated.
func Draw (destination draw.Image, setter *TypeSetter, offset fixed.Point26_6, col color.Color) image.Rectangle {
	source := image.NewUniform(col)
	face   := setter.Face()
	var updatedRegion image.Rectangle
	bounds := destination.Bounds()
	
	setter.Runes()(func (position fixed.Point26_6, run rune) bool {
		// leave empty space for space characters
		if unicode.IsSpace(run) {
			return true
		}
		
		dot := offset.Add(position)
		destinationRectangle, mask, maskPoint, _, ok := face.Glyph(dot, run)
		
		if ok {
			// don't bother drawing runes that are out of bounds
			if destinationRectangle.Min.Y > bounds.Max.Y      { return false }
			if destinationRectangle.Intersect(bounds).Empty() { return true  }

			// draw rune
			draw.DrawMask (
				destination,
				destinationRectangle,
				source, image.Point { },
				mask, maskPoint,
				draw.Over)
		} else {
			// draw tofu
			drawTofu(run, destination, dot, face, col)
		}


		updatedRegion = updatedRegion.Union(destinationRectangle)
		return true
	})
	
	return updatedRegion
}

func drawTofu (
	char rune,
	destination draw.Image,
	position    fixed.Point26_6,
	face        font.Face,
	col         color.Color,
) {
	bounds, _ := tofuBounds(face)
	rectBounds := internal.RoundRect(bounds).Add(image.Pt (
		position.X.Round(),
		position.Y.Round()))
	internal.DrawRectangleOutline(destination, rectBounds, col)
}