Description

This example shows how to use the TCanvas drawing functions and their results.

The TCanvas drawing functions are: DrawArc, DrawBitmap, DrawEllipse, DrawLine, DrawPath, DrawPolygon, DrawRect, DrawRectSides, CreateThumbnail.

To build and test this example, create a Multi-Device Application - C++ and add the following controls on the form:

A TImage
A TGroupBox with nine TRadioButton objects (a radio button for each function). Change the TRadioButton.Text property for each radio button to the name of a function.
A TButton

The example draws on the canvas of the bitmap. The bitmap is displayed on the TImage.

Code

Add the following code to the OnCreate event handler of the form.

void __fastcall TForm1::FormCreate(TObject *Sender) {
	// sets the size of the TBitmap  
	Image1->Bitmap->SetSize(int(Image1->Width),int(Image1->Height));
	Image1->Bitmap->Clear(TAlphaColorRec::White);
}

Add the following code, which makes the drawing area white, to the OnClick event handler of the button.

void __fastcall TForm2::Button1Click(TObject *Sender) {
	// clears the canvas
	Image1->Bitmap->Clear(TAlphaColorRec::White);
}

Add the following codes to the OnClick event handlers of each radio button.

Code

void __fastcall TForm1::DrawArcClickClick(TObject *Sender) {
	// sets the center and the radius of the arc
	TPointF p1(200, 200), p2(150, 150);
	Image1->Bitmap->Canvas->BeginScene();
	// draws the arc on the canvas
	Image1->Bitmap->Canvas->DrawArc(p1, p2, 90, 230, 20);
	Image1->Bitmap->Canvas->EndScene();
}
// ---------------------------------------------------------------------------

void __fastcall TForm1::DrawBitmapClick(TObject *Sender) {
	TBitmap* MyBitmap;
	// is the area where to draw the bitmap
	// is also the area of the bitmap to be drawn on the canvas 
	TRectF MyRect(50, 30, 150, 200);
	// MyBitmap is the bitmap to be drawn on the canvas
	MyBitmap = new TBitmap("bitmap1.png");
	Image1->Bitmap->Canvas->BeginScene();
	// draws on the rectangle specified by MyRect the area from MyBitmap specified by MyRect
	Image1->Bitmap->Canvas->DrawBitmap(MyBitmap, MyRect, MyRect, 20);
	Image1->Bitmap->Canvas->EndScene();
}
// ---------------------------------------------------------------------------

void __fastcall TForm1::DrawEllipseClick(TObject *Sender) {
	// sets the circumscribed rectangle of the ellipse
	TRectF MyRect(50, 40, 200, 270);
	Image1->Bitmap->Canvas->BeginScene();
	// draws the ellipse on the canvas
	Image1->Bitmap->Canvas->DrawEllipse(MyRect, 40);
	Image1->Bitmap->Canvas->EndScene();
}
// ---------------------------------------------------------------------------

void __fastcall TForm1::DrawLineClick(TObject *Sender) {
	// p1 and p2 represent the ends of the line to be drawn
	TPointF p1(20, 2), p2(350, 400);
	Image1->Bitmap->Canvas->BeginScene();
	// draws the line on the canvas
	Image1->Bitmap->Canvas->DrawLine(p1, p2, 100);
	Image1->Bitmap->Canvas->EndScene();
}
// ---------------------------------------------------------------------------

void __fastcall TForm1::DrawPathClick(TObject *Sender) {
	TPathData* path;
	// sets the circumscribed rectangle of the ellipse to be added to the path
	TRectF MyRect1(90, 100, 230, 300), MyRect2(70, 90, 220, 290);
	// initializes and creates the path to be drawn
	path = new TPathData;
	path->AddEllipse(MyRect1);
	path->AddRectangle(MyRect2, 0, 0, AllCorners);
	// draws the path on the canvas
	Image1->Bitmap->Canvas->BeginScene();
	Image1->Bitmap->Canvas->DrawPath(path, 200);
	Image1->Bitmap->Canvas->EndScene();
}
// ---------------------------------------------------------------------------

void __fastcall TForm1::DrawPolygonClick(TObject *Sender) {
	// sets the points that define the polygon
	TPointF p1(80, 200), p2(225, 30), p3(370, 200), p4(300, 340),
		p5(150, 340), p6(80,200);
	TPolygon MyPolygon;
	// creates the polygon
	MyPolygon.set_length(6);
	MyPolygon[0] = p1;
	MyPolygon[1] = p2;
	MyPolygon[2] = p3;
	MyPolygon[3] = p4;
	MyPolygon[4] = p5;
        MyPolygon[5] = p6;
	Image1->Bitmap->Canvas->BeginScene();
	// draws the polygon on the canvas
	Image1->Bitmap->Canvas->DrawPolygon(MyPolygon, 50);
	Image1->Bitmap->Canvas->EndScene();
}
// ---------------------------------------------------------------------------

void __fastcall TForm1::DrawRectClick(TObject *Sender) {
	// sets the rectangle to be drawn
	TRectF MyRect(50, 40, 200, 270);
	Image1->Bitmap->Canvas->BeginScene();
	// draws the rectangle on the canvas
	Image1->Bitmap->Canvas->DrawRect(MyRect, 30, 60, AllCorners, 100);
	Image1->Bitmap->Canvas->EndScene();
}
// ---------------------------------------------------------------------------

void __fastcall TForm1::DrawRectSidesClick(TObject *Sender) {
	// sets the rectangle to be customized and drawn
	TRectF MyRect(50, 40, 200, 270);
	Image1->Bitmap->Canvas->BeginScene();
	// customizes the rectangle and draws it on the canvas
	Image1->Bitmap->Canvas->DrawRectSides(MyRect, 50, 20, AllCorners, 40,
		AllSides, TCornerType(1));
	Image1->Bitmap->Canvas->EndScene();
}
// ---------------------------------------------------------------------------

void __fastcall TForm1::CreateThumbnailClick(TObject *Sender) {
	// creates the bitmap from where to draw the thumbnail
	TBitmap* MyBitmap = new TBitmap("bitmap1.png");
	// draws a thumbnail with the given sizes
	Image1->Bitmap = MyBitmap->CreateThumbnail(300,300);
}
// ---------------------------------------------------------------------------