Visual Basic 'NET BASICS

1
Visual Basic .NET BASICS

• Lesson 15
• Lines and Shapes

2
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.

3
Objectives (continued)

• Draw polygrams.
• Create images made up of multiple objects drawn
  on a form.

4
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.

5
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.

6
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.

7
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.

8
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.

9
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.

10
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.

11
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.

12
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.

13
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.

14
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.

15
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.

16
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.