TCanvas.Create Constructor

Creates an instance of TCanvas.

Pascal

constructor Create;

C++

__fastcall TCanvas();

Description

Call Create to instantiate a TCanvas object at runtime. Create allocates memory for the instance of TCanvas and creates the TFont, TBrush and TPen objects for the Font, Brush, and Pen properties. Create also initializes the CopyMode to cmSrcCopy.

C++ Examples:

Copy Code

/*
The GetFormImage allows you to easily obtain a bitmap of a
form. The following method can be added to a custom
TWinControl descendant to save itself as a bitmap.  Check the
produced BMP file to confirm.  Click the button and them
double click on the newly created foo.bmp file to view.
*/

#include <memory>       //for STL auto_ptr class

class TMyControl : public TColorListBox
{
__published:    // IDE-managed Components
    void __fastcall SaveAsBmp(TFileName fileName);
private:    // User declarations
public:     // User declarations
    __fastcall TMyControl(TComponent* Owner);
};

TForm1 *Form1;
TMyControl *MyControl1;

__fastcall TForm1::TForm1(TComponent* Owner)
    : TForm(Owner)
{
}

__fastcall TMyControl::TMyControl(TComponent* Owner)
    : TColorListBox(Owner)
{
}

typedef struct {
  TLogPalette lpal;
  TPaletteEntry dummy[256];
} LogPal;

void __fastcall TMyControl::SaveAsBmp(TFileName fileName)
{
  std::auto_ptr<TCanvas> tempCanvas(new TCanvas);
  HWND notUsed;
  tempCanvas->Handle = GetDeviceContext(notUsed);
  std::auto_ptr<TImage> image2save(new TImage(Form1)); // The owner will clean this up.
  image2save->Height = Height;
  image2save->Width = Width;
  TRect destRect = Rect(0,0,Width,Height);
  TRect sourceRect = destRect;
  image2save->Canvas->CopyRect(destRect, tempCanvas.get(), sourceRect);
  LogPal SysPal;
  SysPal.lpal.palVersion = 0x300;
  SysPal.lpal.palNumEntries = 256;
  GetSystemPaletteEntries(tempCanvas->Handle,0,256,SysPal.lpal.palPalEntry);
  image2save->Picture->Bitmap->Palette =
    CreatePalette(dynamic_cast<const tagLOGPALETTE *>(&SysPal.lpal));
  image2save->Picture->SaveToFile(fileName);
}

void __fastcall TForm1::Button1Click(TObject *Sender)
{
  static_cast<TMyControl*>(MyControl1)->SaveAsBmp("../foo.bmp");
}

void __fastcall TForm1::FormCreate(TObject *Sender)
{
  TMyControl* control = new TMyControl(Form1); // The owner will clean this up.
  
  MyControl1 = control;
  control->Parent = this;
  control->Visible = true;
}

Delphi Examples:

Copy Code

{
The GetFormImage allows you to easily obtain a bitmap of a
form. The following method can be added to a custom
TWinControl descendant to save itself as a bitmap.  Check the
produced BMP file to confirm.  Click the button and then
double click on the newly created foo.bmp file to view.
}
type
  TMyControl = class(TColorListBox)
    procedure SaveAsBmp(fileName: TFileName);
  end;
  TForm1 = class(TForm)
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
    procedure FormCreate(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;
  MyControl1: TMyControl;
implementation

{$R *.dfm}

type
  LogPal = record
  lpal : TLogPalette;
  dummy:Array[0..255] of TPaletteEntry;
  end;  

procedure TMyControl.SaveAsBmp(fileName: TFileName);
var
  Source: TComponent;
  SysPal : LogPal;
  tempCanvas: TCanvas;
  sourceRect, destRect: TRect;
  image2save: TImage;
  notUsed: HWND;
begin
  tempCanvas := TCanvas.Create;
  try
    tempCanvas.Handle := GetDeviceContext(notUsed);
    image2save:=TImage.create(self);
    try
      with image2save do
      begin
        Height := Self.Height;
        Width :=  Self.Width;
        destRect := Rect(0,0,Width,Height);
        sourceRect := destRect;
        Canvas.CopyRect(destRect,tempCanvas,sourceRect);
        SysPal.lPal.palVersion:=$300;
        SysPal.lPal.palNumEntries:=256;
        GetSystemPaletteEntries(
          tempCanvas.Handle,0,256,SysPal.lpal.palPalEntry);
        Picture.Bitmap.Palette:= CreatePalette(Syspal.lpal);
      end;
      image2save.Picture.SaveToFile(fileName);
    finally
     image2save.Free;
    end;
  finally
    tempCanvas.Free;
  end;
end;
procedure TForm1.Button1Click(Sender: TObject);
begin
  MyControl1.SaveAsBmp('foo.bmp');
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  MyControl1:= TMyControl.Create(Form1);
  MyControl1.Parent:= Form1;
  MyControl1.visible := true;
end;