GAMBAS BOOK 3.19.1

The Paint class (gb.qt4) only has (static) methods. The many methods are grouped together in the tables below to make it easier to visualise relationships. After the tables you will find notes on the use of selected methods and descriptions of the parameters.

You should definitely take a look at the Painting project from the Gambas examples, as it not only demonstrates drawing with the Paint class, but also shows the (paint) source code used for the 22 lines and areas:

Figure 23.3.2.1: Project Painting - Example 9: Fill style

The Paint class has these methods:

Tables 23.3.2.4.1 : Methods of the Paint class

The following notes supplement the contents of the tables. Arguments are described in more detail and special features are pointed out. Examples and complete projects can be found in the following two → chapters 23.3.3 Paint projects 1 and 23.3.4 Paint projects 2.

ClosePath

• ClosePath() is different from a LineTo() with the appropriate coordinates.
• If a closed path (with the first method) is drawn with Stroke(), there are no caps (Paint.LineCap) at the line ends, but the lines are joined (Paint.LineJoin).
• If there is no current point when ClosePath() is called, this method has no effect.

Circle and arc

The notes for an arc are very extensive on the one hand and only valid in certain combinations on the other:

• XM : x-coordinate of the centre of the arc
• YM : y-coordinate of the centre of the arc
• Radius : Radius of the circular arc
• Angle : Starting angle - measured against the positive x-axis
• Length : Measure for the centre angle
• Pie : For True, this results in a closed sector ('pie slice'). Standard is an open arc.
• If Length is negative, the arc is drawn in a clockwise direction.
• If Angle and Length are not specified, a full circle is drawn.
• If the Angle value is specified but not Length, nothing is drawn. The current position is set to the (end) point on the arc.
• To draw an elliptical arc instead of a circular arc, you must use the Ellipse method with suitable arguments.

Figure 23.3.2.4.1: Circular arc - circle sectors

Source code:

Public Sub DrawArcs()
  Paint.AntiAlias = True  
    Paint.LineWidth = 1
    Paint.Brush = Paint.Color(Color.Red)
    Paint.Arc(100, 140, 70, Rad(45), 3 * Pi / 2, False)
    Paint.Stroke()
    Paint.Arc(260, 140, 70, Pi / 4, Rad(270), True)
    Paint.Stroke()
    Paint.Arc(420, 140, 70, Pi / 4, 3 * Pi / 2, True)
    Paint.Fill()
    Paint.Dash = [2, 2]
    Paint.Arc(420, 140, 70, Pi / 4 + 3 * Pi / 2, Rad(90), False)
    Paint.Stroke()
    Paint.Dash = []  '-- Null    
  Paint.AntiAlias = False  
End

Rounded rectangles

If the optional radius argument is defined, the rectangle will have rounded 'corners'. The radius argument determines the radius of the rounding. The radius must not be greater than half of the shortest side of the rectangle.

Polygon - special case triangle

This source code is used to draw a light blue triangle ABC:

Paint.LineWidth = 1
Paint.Brush = Paint.Color(&C3DDFF)
Paint.Polygon([20, 20, 30, 160, 200, 70]) '-- A(20|20), B(30|160) and C(200|70)
Paint.Fill()

Ellipses

Ellipse ( X As Float, Y As Float, Width As Float, Height As Float [ , Angle As Float, Length As Float, Pie As Boolean ] )

• X, Y, Width, Height : bounding box of the ellipse
• Angle : Start angle
• Lenght : Swept angle
• Pie : A closed sector results for True. Standard is an open arc.
• If Length is negative, the elliptical arc is drawn in a clockwise direction.
• If Angle and Length are not specified, a complete ellipse is drawn.
• If the Angle value is specified - but not Length - then nothing is drawn. The current position is set to the (end) point on the ellipse arc.

Cubic Bezier curve

CurveTo ( X1 As Float, Y1 As Float, X2 As Float, Y2 As Float, X3 As Float, Y3 As Float )

• X1 : x-coordinate of the first support point (start point)
• Y1 : y-coordinate of the first support point
• X2 : x-coordinate of the second support point
• Y2 : y-coordinate of the second support point
• X3 : x-coordinate of the third support point (end point)
• Y3 : y-coordinate of the third support point

If there was no current point before the call of Paint.CurveTo(..), the function will behave as if the call was preceded by the Paint.MoveTo(X1|Y1) method to ensure a defined start.

Cubic Bezier curve with relative coordinates - version of CurveTo(..)

RelCurveTo ( X1 As Float, Y1 As Float, X2 As Float, Y2 As Float, X3 As Float, Y3 As Float )

• DX1 : x-offset of the first support point (start point)
• DY1 : y offset of the first support point
• DX2 : x-offset of the second support point
• DY2 : y-offset of the second support point
• DX3 : x-offset of the third support point (end point)
• DY3 : y-offset of the third support point

Paint.CurveTo(X+DX1, Y+DY1, X+DX2, Y+DY2, X+DX3, Y+DY3) is logically equivalent to the call Paint.RelCurveTo (DX1, DY1, DX2, DY2, DX3, DY3) at a current point (X|Y).

Text

Text(Text As String [, X As Float,Y As Float,Width As Float,Height As Float,Alignment As Integer ] )

• X, Y, Width, Height : A rectangle in which the text is drawn
• Alignment : Alignment of the text in the rectangle

If only the text is specified, the text is drawn at the current point. The y-coordinate of the current point determines the BaseLine for the text. The term 'BaseLine' can be described very simply using the word annoyance. Mentally draw a line from the base point of the letter A to the base point of the small r - this is the BaseLine. If only the arguments X and Y are specified next to the text, the text is drawn at the point P(X|Y). The y-coordinate of P determines the BaseLine for the text. Otherwise, the text is drawn within the specified rectangle. Please note that the rectangle does not cut off the text!

RichText

RichText ( Text As String [ , X As Float, Y As Float, Width As Float, Height As Float, Alignment As Integer ] )

• The same notes apply to the optional arguments as for the Text() method.
• As only one path is created, font colours defined by the <font> markup are not taken into account!

TrimText – TrimRichText

TrimText ( Text As String, W As Float [ , H As Float ] ) As String
TrimRichText ( RichText As String, W As Float [ , H As Float ] ) As String

• Text : Text to be customised
• W : Length of the (enclosing) rectangle
• H : optional height of the (enclosing) rectangle. If it is not specified, the font size is assumed. In other words: The text should fit into a single line.

DrawImage

DrawImage ( Image As Image, X As Float, Y As Float [ , Width As Float, Height As Float, Opacity As Float, Source As Rect ] )

• Image : Image to be drawn
• X, Y : Coordinates of the starting point (top left)
• Width, Height : If specified, the image is scaled to width and height
• Opacity : The opacity used to create the image is between 0 (completely transparent) and 1.0 (completely opaque). The default value is 1.
• Source : If specified (data type Rect), only the part of the image described by the rectangle is taken into account.

DrawPicture

DrawPicture ( Picture As Picture, X As Float, Y As Float [ , Width As Float, Height As Float, Source As Rect ] )

• Picture : Picture to be drawn
• X, Y : Coordinates of the starting point
• Width, Height : If specified, the image is scaled to width and height
• Source : If specified (data type Rect), only the part of the image described by the rectangle is taken into account.

DrawTextShadow

DrawTextShadow ( Text As String, X As Float, Y As Float, W As Float, H As Float [ , Alignment As Integer, Radius As Integer, Opacity As Float ] )
DrawRichTextShadow ( Text As String, X As Float, Y As Float, W As Float, H As Float [ , Alignment As Integer, Radius As Integer, Opacity As Float ] )

• X, Y, W, H : Define the rectangle in which the drawing takes place
• Alignment : Determines the alignment of the text, default is Align.Left
• Radius : Blending radius in pixels. By default, the value is 1/8 of the font height
• Opacity : The opacity is between 0.0 and 1.0. The default value is 0.5 (50% transparent)
• You must call Paint.DrawText() or Paint.RichText() to draw the actual text for the shadow.

LinearGradient

LinearGradient ( X0 As Float, Y0 As Float, X1 As Float, Y1 As Float, Colors As Integer[], Positions As Float[] [ , Extend As Integer ] ) As PaintBrush

• X0 : x-coordinate starting point
• Y0 : y-coordinate starting point
• X1 : x-coordinate end point
• Y1 : y-coordinate end point
• The points (X0, Y0) and (X1, Y1) define a line of length L that connects the two points.
• Colors : Array of colour values
• Positions : Array of colour positions; 0 for gradient start and 1 for gradient end. A position q (float) between 0 and 1 corresponds to the point Q on the defined path that is q*L away from the start point and (1-q)*L away from the end point. A position in the position array is also called a stopper. The colour with the same index from the colours array belongs to a stopper. This colour has the greatest intensity at the stopper.
• The following illustration shows a linear gradient from (0|0) to (200|70) across the colours black, yellow and blue. The stoppers are shown as red dots at 0 and 0.3 as well as 1.0.

Figure 23.3.2.4.2: LinearGradient

RadialGradient

RadialGradient (CX As Float,CY As Float,Radius As Float,FX As Float,FY As Float,Colors As Integer[],Positions As Float[] [,Extend As Integer ]) As PaintBrush

• CX : x-coordinate circle centre point
• CY : y-coordinate circle centre point
• Radius : Radius of the circle
• FX : x-coordinate for the gradient centre point
• FY : y coordinate for the gradient centre point
• Colors : Array of colour values (stop)
• Positions : Array of colour positions; 0 for gradient start and 1 for gradient end