Drawing Straight Lines In a Windows VCL Application

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This procedure draws two diagonal straight lines on an image in a VCL form.

1. Create a VCL form.
2. Code the form's OnPaint event handler to draw the straight lines.
3. Build and run the application.

To create a VCL form and place an image on it

1. Open File > New > Windows VCL Application - Delphi
2. In the form view, click the form, if necessary, to display Form1 in the Object Inspector.

To write the OnPaint event handler

1. In the Object Inspector, double-click the Form1 OnPaint event on the Events tab.The Code Editor displays with the cursor in the TForm1.FormPaint event handler block.
2. Enter the following event handling code:

with Canvas do
begin
MoveTo(0,0);
LineTo(ClientWidth, ClientHeight);
MoveTo(0, ClientHeight);
LineTo(ClientWidth, 0);
end; 

Canvas->MoveTo( 0, 0 );
Canvas->LineTo( ClientWidth, ClientHeight );
Canvas->MoveTo( 0, ClientHeight );
Canvas->LineTo( ClientWidth, 0 );

To run the program

1. Choose Run > Run .
2. The applications executes, displaying a form with two diagonal crossing lines.

   Tip: To change the color of the pen to green, insert this statement following the first MoveTo() statement in the event handler code: Pen.Color := clGreen; (Delphi) Canvas->Pen->Color = clGreen; (C++). Experiment using other canvas and pen object properties. See Using the Properties of the Canvas Object in the Windows Developer's Guide.

See Also

• VCL Overview
• How To Build a Windows VCL Application with Graphics
• Drawing Rectangles and Ellipses in a Windows VCL Application
• Drawing a Polygon in a Windows VCL Application
• Displaying a Bitmap Image in a Windows VCL Application