Graphics
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Basic |
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As well as the shape control, there are three Methods that can
be used for producing graphics in Visual Basic.
The three methods are 1. PSet, 2. Line
and 3. Circle.
These methods can be used on a Form, PictureBox, or Printer
object.
DRAWING LINES:
The Line method has the following syntax.
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| Object.Line Step (xStart, yStart)-[Step]
(xEnd, yEnd), PenColour, BF |
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All options except "Line -(xEnd, yEnd)" are optional.
- Step makes co-ordinates relative to CurrentX and CurrentY.
If omitted, the co-ordinates refer to the underlying object with
0, 0 at the top left.
- (xStart, yStart) is the start point for the line.
- PenColour sets the line colour. If omitted, the ForeColor
property will be used instead.
- B will produce a rectangle.
- F will cause a rectangle to be filled
The drawing Object's ScaleWidth and ScaleHeight properties are
useful when drawing lines.
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' Draw a line horizontally across the
centre of the form
Me.Line (0, Me.ScaleHeight / 2)-(Me.ScaleWidth, Me.ScaleHeight
/ 2)
' Draw a line vertically down the centre of the form
Me.Line (Me.ScaleWidth / 2, 0)-(Me.ScaleWidth / 2, Me.ScaleHeight)
' Draw a line from the top left, to the bottom right
Me.Line (0, 0)-(Me.ScaleWidth, Me.ScaleHeight)
' Draw a line from the top right, to the bottom left
Me.Line (Me.ScaleWidth, 0)-(0, Me.ScaleHeight)
' Draw a small red filled box in the top left of the form
Me.Line (100, 100)-(500, 500), RGB(255, 0, 0), BF |
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FREEHAND DRAWING:
The MouseDown event and the MouseMove event are useful
for freehand drawing. If no start position is provided for the Line
method, it draws from CurrentX and CurrentY which
are two system variables that maintain the x and y coordinates for
each of the graphics objects.
Initially when MouseDown is raised, we draw a dot with the PSet
method. This updates both CurrentX and CurrentY. When the MouseMove
event is raised, we draw a line from CurrentX CurrentY to the new
mouse position, which in turn updates the system variables CurrentX
and CurrentY. The mouse position is passed to both the MouseDown
and the MouseMove events. We check the Button status in MouseMove
to ensure the button is pressed, otherwise it would draw whenever
the mouse is moved.
To try this example, copy the code and paste it into
a new project. Run the program, and use the mouse to draw on the
form.
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Option Explicit
Private Sub Form_MouseDown(Button As Integer, Shift As Integer,
X As Single, Y As Single)
Me.PSet (X, Y)
End Sub
Private Sub Form_MouseMove(Button As Integer, Shift As Integer,
X As Single, Y As Single)
If Button = vbLeftButton Then
'
Draw a line from the last position
'
This gives the impression of freehand drawing
Me.Line
-(X, Y)
End If
End Sub |
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DRAWING CIRCLES:
The Circle method has the following syntax.
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| Object.Circle Step (x, y), Radius, Colour,
Start, End, Aspect |
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All options except "Circle (x, y), Radius" are optional.
- Step makes co-ordinates relative to CurrentX and CurrentY.
If omitted, the co-ordinates refer to the underlying object with
0, 0 at the top left.
- (x, y) the centre of the circle.
- Radius the radius of the circle.
- Colour sets the arc colour. If omitted, the ForeColor
property will be used instead.
- Start the start point of the arc (in radians, with 0
starting at the 3 O'Clock position - default = 0).
- End the end point of the arc (in radians, with 0 starting
at the 3 O'Clock position - default = 2 * Pi radians).
- Aspect ratio relative to the height and width of the
bounding rectangle of the circle. The default value is 1, a prefect
circle. A value less than 1 results in a short fat circle, and
a value greater than 1 results in a tall thin circle.
This example draws a short fat circle in the centre of
the form with a radius of 1000 twips.
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| Me.Circle (Me.ScaleWidth / 2, Me.ScaleHeight
/ 2), 1000, , , , 0.5 |
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Notice that when optional values are omitted, the comma is
still used as a placeholder.
The next example draws a series of circles and arcs to
further illustrate the use of the Circle method. The resulting image
is shown below the example.
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Const pi As Double = 3.142
Dim r As Integer
' Draw a circle in the centre of the form
Me.Circle (Me.ScaleWidth / 2, Me.ScaleHeight / 2), 500
' Draw the top half of a semi circle,
' 500 twips above centre
Me.Circle (Me.ScaleWidth / 2, Me.ScaleHeight / 2 - 500), 500,
, 0, pi
' Draw the bottom half of a semi circle,
' 500 twips below centre
Me.Circle (Me.ScaleWidth / 2, Me.ScaleHeight / 2 + 500), 500,
, pi, 0
' Draw the left half of a semi circle,
' 500 twips to the left of centre
Me.Circle (Me.ScaleWidth / 2 - 500, Me.ScaleHeight / 2), 500,
, pi / 2, 1.5 * pi
' Draw the right half of a semi circle,
' 500 twips to the right of centre
Me.Circle (Me.ScaleWidth / 2 + 500, Me.ScaleHeight / 2), 500,
, 1.5 * pi, pi / 2
' Draw a short fat oval in the centre of the form
Me.Circle (Me.ScaleWidth / 2, Me.ScaleHeight / 2), 500, , ,
, 0.5
' Draw a tall thin oval in the centre of the form
Me.Circle (Me.ScaleWidth / 2, Me.ScaleHeight / 2), 500, , ,
, 2
' Set the radius to whichever is the larger,
' the width of the form, or the height
If Me.ScaleWidth > Me.ScaleHeight Then
r = Me.ScaleWidth / 2
Else
r = Me.ScaleHeight / 2
End If
' The shape of the form will determine the aspect ratio
Me.Circle (Me.ScaleWidth / 2, Me.ScaleHeight / 2), r, , , ,
Me.ScaleHeight / Me.ScaleWidth |
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RUBBERBAND EFFECT
This example illustrates how to use a "rubberband"
effect using the Circle method and the DrawMode property. To try
it, copy and paste it into a new project.
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Option Explicit
' Declare variables that are required in more than one event
Dim centreX As Integer, centreY As Integer
Dim Drawing As Boolean
Private Sub Form_MouseDown(Button As Integer, Shift As Integer,
X As Single, Y As Single)
' Determine centre of circle
centreX = X
centreY = Y
End Sub
Private Sub Form_MouseMove(Button As Integer, Shift As Integer,
X As Single, Y As Single)
Static oldX As Integer, oldY As Integer
If Button = vbLeftButton Then
' Change the
drawing mode to invert whatever is on
' the canvas
in order to preserve existing drawing
Me.DrawMode
= vbInvert
' If we've started
drawing a circle, we need to
'
delete the old circle
If
Drawing = True Then
'
Calculate the radius of the circle using Pythagoras' theory
'
In a right angled triangle, the square on the hypotenuse
'
is equal to the sum of the areas of the squares on the
'
other two sides. This ensures that the circumference of the
'
circle passes through the current mouse cursor position
Me.Circle
(centreX, centreY), Sqr((centreX - oldX) ^ 2 + (centreY - oldY)
^ 2)
End
If
' Draw new circle
' Use Pythagoras
to calculate radius
Me.Circle (centreX,
centreY), Sqr((centreX - X) ^ 2 + (centreY - Y) ^ 2)
' Store the
current mouse coordinates
oldX = X
oldY = Y
Drawing = True
End If
End Sub
Private Sub Form_MouseUp(Button As Integer, Shift As Integer,
X As Single, Y As Single)
' Change the drawing mode to overwrite
whatever is on the canvas
Me.DrawMode = vbCopyPen
Me.Circle (centreX, centreY), Sqr((centreX
- X) ^ 2 + (centreY - Y) ^ 2)
Drawing = False
End Sub |
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PLOTTING POINTS:
The PSet method has the following syntax.
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| Object.PSet Step (x, y), Colour |
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All options except "PSet (x, y)" are optional.
- Step makes co-ordinates relative to CurrentX and CurrentY.
If omitted, the co-ordinates refer to the underlying object with
0, 0 at the top left.
- (x, y) the co-ordinates for the point to be set.
- Colour sets the arc colour. If omitted, the ForeColor
property will be used instead.
This example draws a point 5 pixels wide in the centre of the
Form.
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Me.DrawWidth = 5
Me.PSet (Me.ScaleWidth / 2, Me.ScaleHeight / 2) |
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GRAPHICS PROPERTIES:
The following is a list of properties for Visual Basic's Graphics
objects.
The ScaleMode Graphics Property
The ScaleMode Property is used to determine the units used
for drawing.
ScaleMode
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| Mode |
Constant |
Description |
| 0 |
vbUser |
Used when ScaleHeight, ScaleWidth, ScaleLeft,
and ScaleTop properties have custom values |
| 1 |
vbTwips |
Twentieth of a printer's point (default) |
| 2 |
vbPoints |
A printer's point (72 points to the inch) |
| 3 |
vbPixels |
The smallest unit of monitor or printer resolution
(machine dependent) |
| 4 |
vbCharacters |
120 x 240 twips per unit |
| 5 |
vbInches |
Measured in inches |
| 6 |
vbMillimeters |
Measured in millimeters |
| 7 |
vbCentimeters |
Measured in centimeters |
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The following sets the ScaleMode of the form to inches.
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DRAW MODE
The DrawMode Property is used to determine how the graphical
methods will be drawn over the background of the Graphic Object.
DRAWMODE
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| Mode |
Constant |
Description |
| 1 |
vbBlackness |
Black Pen |
| 2 |
vbNotMergePen |
Inverse of Merge Pen, mode 15 |
| 3 |
vbMaskNotPen |
Combination of background and inverse pen |
| 4 |
vbNotCopyPen |
Inverse of Copy Pen, mode 13 |
| 5 |
vbMaskPenNot |
Combination of pen and inverse of background |
| 6 |
vbInvert |
Inverse the display |
| 7 |
vbXorPen |
Combination of the pen and the display, but not
both |
| 8 |
vbNotMaskPen |
Inverse setting of Mask Pen, mode 9 |
| 9 |
vbMaskPen |
Combination of the pen and the background |
| 10 |
vbNotXorPen |
Inverse of Xor Pen, mode 7 |
| 11 |
vbNop |
Output unchanged |
| 12 |
vbMergeNotPen |
Combination of background and the inverse of the
pen colour |
| 13 |
vbCopyPen |
Colour specified by the ForeColor Property (default) |
| 14 |
vbMergePenNot |
Combination of pen colour and the inverse of the
background |
| 15 |
vbMergePen |
Combination of the pen colour and the display |
| 16 |
vbWhiteness |
White Pen |
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The following changes the DrawMode of the form to the inverse
of the background.
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DRAWSTYLE
The DrawStyle Property is used to determine the line style
of the Graphics Object.
DrawStyle
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| Style |
Constant |
Description |
| 0 |
vbSolid |
Default - solid |
| 1 |
vbDash |
Dash |
| 2 |
vbDot |
Dot |
| 3 |
vbDashDot |
Dash-Dot |
| 4 |
vbDashDotDot |
Dash-Dot-Dot |
| 5 |
vbInvisible |
Transparent |
| 6 |
vbInsideSolid |
Inside solid |
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The following sets the DrawStyle of the form to Dotted.
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DrawWidth
The DrawWidth property determines the width for output with
the graphic methods. The width setting is in pixels regardless of
the ScaleMode unit.
The following example sets the drawing mode to Invert,
the style to dotted, and the width to 5 pixels on a form.
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Me.ScaleMode = vbInches
Me.DrawMode = vbInvert
Me.DrawStyle = vbDot
Me.DrawWidth = 5
Me.Line (0, 0)-(1, 1) |
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FILLSTYLE
The FillStyle Property is used to determine how to fill Graphics
Objects.
FillStyle
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| Style |
Constant |
Description |
| 0 |
vbFSSolid |
Default - solid |
| 1 |
vbFSTransparent |
Transparent (Default) |
| 2 |
vbHorizontalLine |
Filled with horizontal lines |
| 3 |
vbVerticalLine |
Filled with vertical lines |
| 4 |
vbUpwardDiagonal |
Filled with upward diagonal lines |
| 5 |
vbDownwardDiagonal |
Filled with downward diagonal lines |
| 6 |
vbCross |
Filled with horizontal and vertical lines |
| 7 |
vbDiagonalCross |
Filled with diagonal crossed lines |
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The following sets the FillStyle of the form to crossed.
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SPECIFYING COLOURS:
The RGB function allows colours to be defined using ranges
between 0 and 255 for red, green and blue. The values are passed
to the function in the order red, green, blue - hence the function
name RGB. A value of 0 means none of the colour, and a value of
255 means full intensity of that colour.
For example, red can be set using RGB(255, 0, 0). Intermediate
colours can be defined using intermediate values. For example, grey
can be set using RGB(128, 128, 128).RGB(0, 0, 0) is used to specify
Black, and RGB(255, 255, 255) is used to specify White.
The following example sets for Form's ForeGround property
to Magenta. Any graphics methods used will be drawn using this colour,
unless overridden within the function.
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| Me.ForeColor = RGB(255, 0, 255) |
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The following colour constants may also be used to specify colours
in Visual Basic.
COLOUR CONSTANTS:
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| Constant |
Hexadecimal Value |
Colour |
| vbBlack |
&H0 |
Black |
| vbRed |
&HFF |
Red |
| vbGreen |
&HFF00 |
Green |
| vbYellow |
&HFFFF |
Yellow |
| vbBlue |
&HFF0000 |
Blue |
| vbMagenta |
&HFF00FF |
Magenta |
| vbCyan |
&HFFFF00 |
Cyan |
| vbWhite |
&HFFFFFF |
White |
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The following sets the form's ForeColor property to red.
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SMALL DRAWING PACKAGE
This example uses the graphics features mentioned above to produce
a drawing package.
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