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Visual Basic .NET BASICS. Lesson 15 Lines and Shapes. Objectives. Explain the coordinate system used to position graphical objects on a form. Draw lines from code. Draw boxes and rectangles from code. Draw circles and ellipses from code. Objectives (continued). Draw polygrams.
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Visual Basic .NET BASICS Lesson 15 Lines and Shapes
Objectives • Explain the coordinate system used to position graphical objects on a form. • Draw lines from code. • Draw boxes and rectangles from code. • Draw circles and ellipses from code.
Objectives (continued) • Draw polygrams. • Create images made up of multiple objects drawn on a form.
Drawing Objects Using Code • Visual Basic .NET provides a single Graphic object with a large number of methods that allow a program to draw on a form. • A Graphics object is a general-purpose drawing surface that may be used with a number of graphical tools in Visual Studio .NET.
Understanding Coordinates • In order to begin working with drawing objects, you must first understand the coordinate system on a form. • The top-left point on a form has an X coordinate of zero and a Y coordinate of zero. • To use the DrawLine method, you need to think in terms of X and Y rather than top and left. • The combination of the X and Y value is called a Point.
Understanding Pens and Brushes • After specifying the location of an object, you will also have to specify a Pen or Brush to use to draw the object. • A pen is used to draw lines or the outline of a shape. • A brush is used to fill in shapes or to draw text.
Using the DrawLine Method • To use the DrawLine method, you must specify the endpoints of the line you want to draw and the pen you want to use to draw the line. • You can also create a Pen inside the DrawLine statement.
Drawing Rectangles and Boxes • Rectangles and boxes can be drawn in two different ways: • The DrawRectangle method uses a Pen object and is used to draw the outline of a rectangle. • The FillRectangle method uses a Brush object and is used to draw a rectangle that is filled in. • The rectangle is created with an X and Y location for its top-left corner and two other parameters that will specify the width and height properties.
Drawing Circles and Ellipses • Like rectangles, circles and ellipses can either be drawn as outlines or as filled objects. • The parameters for the DrawEllipse method are a Pen object, the location of the ellipse, and the width and height of the ellipse. • The FillEllipse method uses the same location and size parameters, but uses a Brush object in place of a Pen object.
Drawing Polygons • A polygon is any shape with three or more sides. • The DrawPolygon method takes a Pen as its first parameter. • The second parameter is an array of points. • The array has one element less than the number of sides in the polygon.
Locating the Mouse • The MouseDown event returns a number of useful pieces of information. • It returns the location on the form where the mouse was pointing when the mouse button was pressed. • This variable, ”e,” has an X and Y coordinate and holds the location where the mouse was clicked. • This will allow your program to draw wherever the user wishes to draw.
Clearing the Form • The form can be cleared in two ways: • Parts of the form may be cleared by drawing new shapes over existing shapes. • Another way is to use the Clear method of the Graphics objects.
Summary • You can use the DrawLine method to draw a line on a form using Visual Basic. NET code. • There are two ways to draw most shapes on a form. A Draw method creates an outline drawing of the object. The Fill method creates an object that is filled with a color specified by a brush color. • A Pen object is created with a color and may also have a line specified for it.
Summary (continued) • Rectangles (including squares) are created using the DrawRectangle and FillRectangle methods. Rectangles are objects that can be declared with a starting point and width and height. Once they are declared, rectangle objects can be used to draw both rectangles and ellipses. • Ellipses (including circles) are created using the DrawEllipse and FillEllipse methods.
Summary (continued) • Once you have drawn a line, rectangle, ellipse, or other shape with a graphic method, you cannot manipulate it. The graphic methods draw directly on a form. • The MouseDown event returns information about the location of the mouse and the button that was used to click on the mouse. • The Clear method of the Graphics object is used to erase the whole form.
Summary (continued) • Distance and position on a form is mea-sured using coordinates. The top-left corner of a form has the coordinates (0, 0). All coordinates are positive. As you move toward the bottom of a form, the X-coordi-nate value increases. As you move toward the right of a form, the Y-coordinate value increases.
