added rectangle package

rectangle /rectangle.go

@@ -0,0 +1,40 @@
+package rectangle
+
+import (
+	"errors"
+	"image"
+	"image/color"
+
+	"github.com/anthonynsimon/bild/parallel"
+)
+
+//AddRectangle adds rectangle to the passes image
+//it uses image to operate on
+//definations of arguments are :
+//	 img  : input image
+//   xLeft : x value of  top left most corner of rectangle to be drawn
+//   yLeft : y value of top left most corner of rectangle to be drawn
+//   xRight : x value of bottom right most corner of rectangle to be drawn
+//   yRight : y value of bottom right  most corner of rectangle to be drawn
+// 	 c : color for the inner rectangle
+func AddRectangle(img *image.RGBA, xLeft, yLeft, xRight, yRight int, c color.Color) error {
+
+	height, width := img.Rect.Dy(), img.Rect.Dx()
+	if xRight > width || yRight > height {
+		return errors.New("bottom right corner values exceed the limit")
+	} else if xLeft < 0 || yLeft < 0 {
+		return errors.New("top left corner values preceed the limit")
+	} else if xLeft > xRight || yLeft < yRight {
+		return errors.New("values must be in correct order")
+	}
+	height, width = yLeft-yRight, xRight-xLeft
+	parallel.Line(height, func(start, end int) {
+		for y := start; y < end; y++ {
+			for x := 0; x < width; x++ {
+				img.Set(x+xLeft, y+yRight, c)
+			}
+		}
+	})
+
+	return nil
+}