Add drawing functions

draw.go

@@ -0,0 +1,103 @@
+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"
+
+// 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
+}
+
+// DrawBounds draws the LayoutBounds, MinimumSize, and LayoutBoundsSpace of a
+// TypeSetter to the given image.
+func DrawBounds (destination draw.Image, setter *TypeSetter, offset fixed.Point26_6) {
+	blue  := color.RGBA { B: 255, A: 255 }
+	red   := color.RGBA { R: 255, A: 255 }
+	green := color.RGBA { G: 255, A: 255 }
+
+	layoutBoundsSpace := setter.LayoutBoundsSpace()
+	layoutBounds      := setter.LayoutBounds()
+	
+	minimum     := setter.MinimumSize()
+	minimumRect := roundRect(fixed.Rectangle26_6 { Max: minimum }.Add(offset).Add(layoutBounds.Min))
+	drawRectangleOutline(destination, minimumRect, green)
+	
+	drawRectangleOutline(destination, roundRect(layoutBoundsSpace.Add(offset)), blue)
+	drawRectangleOutline(destination, roundRect(layoutBounds.Add(offset)), red)
+}
+
+func drawTofu (
+	char rune,
+	destination draw.Image,
+	position    fixed.Point26_6,
+	face        font.Face,
+	col         color.Color,
+) {
+	bounds, _ := tofuBounds(face)
+	rectBounds := roundRect(bounds).Add(image.Pt (
+		position.X.Round(),
+		position.Y.Round()))
+	drawRectangleOutline(destination, rectBounds, col)
+}
+
+func drawRectangleOutline (destination draw.Image, bounds image.Rectangle, col color.Color) {
+	for x := bounds.Min.X; x < bounds.Max.X; x ++ {
+		destination.Set(x, bounds.Min.Y, col)
+	}
+	for y := bounds.Min.Y; y < bounds.Max.Y; y ++ {
+		destination.Set(bounds.Min.X, y, col)
+		destination.Set(bounds.Max.X - 1, y, col)
+	}
+	for x := bounds.Min.X; x < bounds.Max.X; x ++ {
+		destination.Set(x, bounds.Max.Y - 1, col)
+	}
+}
+
+func roundRect (rectangle fixed.Rectangle26_6) image.Rectangle {
+	return image.Rect (
+		rectangle.Min.X.Round(),
+		rectangle.Min.Y.Round(),
+		rectangle.Max.X.Round(),
+		rectangle.Max.Y.Round())
+}