delphi fmx DrawBitmap function

Question

On the exemple below, you can see that the application draws two bitmaps (Yellow and Blue) of 256x256 pixels side by side horizontally (0-255 and 256-511) on a red backgroud rectangle (512x260). There is no scaling. The question is, why a vertical pixels line of the background (red) can be viewed between the two ? Delphi 10.1

unit Unit1;

interface

uses
  System.SysUtils, System.Types, System.UITypes, System.Classes,
    System.Variants,
  FMX.Types, FMX.Controls, FMX.Forms, FMX.Graphics, FMX.Dialogs, FMX.Objects,
  FMX.Controls.Presentation, FMX.StdCtrls;

type
  TForm1 = class(TForm)
    PaintBox1: TPaintBox;
    procedure PaintBox1Paint(Sender: TObject; Canvas: TCanvas);
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
  private
    { Private declarations }
    bm1: TBitmap;
    bm2: TBitmap;
    br: TStrokeBrush;
    bShift: Boolean;
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.fmx}

procedure TForm1.FormCreate(Sender: TObject);
begin
  bm1 := TBitmap.Create(256, 256);
  if bm1.Canvas.BeginScene then
    try
      bm1.Canvas.Fill.Color := TAlphaColorRec.Yellow;
      bm1.Canvas.FillRect(RectF(0, 0, bm1.Width, bm1.Height
        ),
        0, 0, AllCorners, 1);
    finally
      bm1.Canvas.EndScene;
    end;
  bm2 := TBitmap.Create(256, 256);
  if bm2.Canvas.BeginScene then
    try
      bm2.Canvas.Fill.Color := TAlphaColorRec.Blue;
      bm2.Canvas.FillRect(RectF(0, 0, bm2.Width, bm2.Height
        ),
        0, 0, AllCorners, 1);
    finally
      bm2.Canvas.EndScene;
    end;

end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  bm1.Free;
  bm2.Free;
end;

procedure TForm1.PaintBox1Paint(Sender: TObject; Canvas: TCanvas);
var
  RecPic: TRectF;
  RecCanvas: TRectF;
  RecCanvas2: TRectF;
begin
  if Canvas.BeginScene then
    try
      Canvas.Fill.Color := TAlphaColorRec.White;
      Canvas.FillRect(RectF(0, 0, PaintBox1.Width, PaintBox1.Height
        ),
        0, 0, AllCorners, 1);

      Canvas.Fill.Color := TAlphaColorRec.Red;
      Canvas.FillRect(RectF(0, 0, 511, 260
        ),
        0, 0, AllCorners, 1);
      RecPic := RectF(0, 0, 255, 255);
      RecCanvas := RectF(0, 0, 255, 255);
      Canvas.DrawBitmap(bm1, RecPic, RecCanvas, 1);

      RecCanvas2 := RectF(256, 0, 511, 255);
      Canvas.DrawBitmap(bm2, RecPic, RecCanvas2, 1);
    finally
      Canvas.EndScene;
    end;
end;

end.

Thanks a lot

Dmitriy Nekrasov Dmitriy Nekrasov · Accepted Answer · 2016-09-03T10:02:46

You must use RecCanvas as RectF(0, 0, 256, 256) and RecCanvas2 as RectF(256, 0, 512, 256), because right and bottom borders are excluded from bitmap drawing area

delphi fmx DrawBitmap function

1 Answers