Graphics

From Xojo Documentation

Revision as of 17:18, 19 November 2020 by GOLone (talk | contribs) (Move Handle from Properties to Methods)


For web apps, see WebGraphics.

Class (inherits from Object)

Graphics class objects are used for drawing text, lines, rectangles, ovals, and pictures.

Enumerations
HandleTypes LineCapTypes LineJoinTypes
Properties
AntiAliasMode FontAscent fa-lock-32.png LineJoin
AntiAliased FontName PenSize
Bold FontSize PrintingCancelled fa-lock-32.png
Brush FontUnit ScaleX
CharacterSpacing Height fa-lock-32.png ScaleY
Copies fa-lock-32.png Italic ShadowBrush
DrawingColor LastPage fa-lock-32.png Transparency
FirstPage fa-lock-32.png LineCap Underline
Font LineDashOffset Width fa-lock-32.png
Methods
ClearRectangle DrawPicture FillRoundRectangle
Clip DrawRectangle Handle
DrawCautionIcon DrawRoundRectangle LineDash
DrawLine DrawStopIcon NextPage
DrawNoteIcon DrawText TextDirection
DrawObject FillOval TextHeight
DrawOval FillPath TextWidth
DrawPath FillRectangle

Notes

Normally you use a graphics object in response to a Canvas.Paint event, but you can also perform direct drawing by using the Graphics property of a Picture. Alternatively, you can create vector graphics using the subclasses of the Object2D class.

fa-info-circle-32.png
You cannot create a meaningful Graphics object via the New command.

Coordinates

The X and Y parameters of the methods are the horizontal and vertical coordinates of the left-top corner of the object being drawn or cleared. The origin (0,0) is the top-left corner of the control or window in which the drawing is being done.
For example, 50,50 is 50 pixels to the right and 50 pixels down from the top-left of the window or control.

Alpha Channel Support

The Transparency property takes a value between 0.0 (opaque) and 100.0 (transparent) that can be used to obtain "fading" effects (amongst other uses) by setting the transparency to a value greater than 0.0.

When rendering colors or pictures with alpha channel information, the Transparency property is composited with the alpha channel information. This allows you to perform uniform fading operations easily and efficiently.

On Windows, using the Transparency property only works on Picture.Graphics if the Picture was created with a depth of 32, or is a Picture with an alpha channel. Attempting to use it on other forms of Pictures will result in an UnsupportedOperationException.

Sample Code

This example uses the Paint event handler of a Canvas control to draw the text “The quick brown fox” in Helvetica bold, italic, 18 point, 50 pixels from the top of and 10 pixels from the left side of the control.

Sub Paint(g As Graphics)
g.Bold = True
g.Italic = True
g.FontName = "Helvetica"
g.FontSize = 18
g.DrawText("The quick brown fox", 10, 50)

This example draws a triangle in a Canvas control. It is placed in the Paint event. The parameter g as Graphics is passed into this event.

Var points() As Integer
points = Array(10, 10, 100, 50, 10, 200, 10, 10)
g.DrawingColor = RGB(100, 200, 255)
g.FillPolygon(points)

This example uses the Clip method to define child Graphics items within the parent Canvas. The code is in the Paint event of a Canvas. The two clippings define regions at the top of the canvas and the DrawOval method draws object in each one. Notice that the first call tries to draw an oval that is wider than the region. It is truncated in the drawing.

Var myClip As Graphics = g.Clip(0, 0, 150, 15)
Var myClip2 As Graphics = g.Clip(150, 0, 150, 15)

// draw the border of the Canvas..
g.DrawingColor = &c000000
g.DrawRectangle(0, 0, g.Width, g.Height)

// draw into the first area...
myClip.DrawingColor = &cff0000
myClip.DrawRectangle(0, 0, myClip.Width, myClip.Height) // draw the border of the area..
myClip.DrawOval(0, 0, 200, 15) // the oval does not appear outside the region despite the call

// draw into the second area...
myClip2.DrawingColor = &c0000ff
myClip2.DrawRectangle(0, 0, myClip2.Width, myClip2.Height) // draw the border of the area
myClip2.DrawOval(0, 0, 150, 15)

See Also

Canvas control; Window, ContainerControl, Group2D classes.