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POHow does Delphi XE2 Firemonkey's Align property set to alScale affect the coordinate system?
 

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  1. POHow does Delphi XE2 Firemonkey's Align property set to alScale affect the coordinate system?
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    <p>How does Delphi XE2 Firemonkey's Align property set to alScale affect the coordinate system?</p> <p>I am looking at Firemonkey's canvas drawing capabilities and came across problems with the coordinates system when a component's Align property is set to alScale. The following demonstration program (a FM HD application) illustrates the problem. Compile and run the sample code, draw a couple of lines, then change the form's size for the weirdness to begin. The lines do not appear at the expected locations.</p> <p>Any suggestions and explanations would be greatly appreciated! Thanks in advance.</p> <p>The main form (LineDrawFormUnit.pas):</p> <pre><code>unit LineDrawFormUnit; interface uses System.SysUtils, System.Types, System.UITypes, System.Classes, System.Variants, FMX.Types, FMX.Controls, FMX.Forms, FMX.Dialogs, FMX.Objects; type TLineDrawForm = class(TForm) Image1: TImageControl; Panel1: TPanel; Label1: TLabel; Label2: TLabel; lX: TLabel; lY: TLabel; { These event handlers are set in the IDE's object inspector } procedure Image1MouseDown(Sender: TObject; Button: TMouseButton; Shift: TShiftState; X, Y: Single); procedure Image1MouseUp(Sender: TObject; Button: TMouseButton; Shift: TShiftState; X, Y: Single); { This event handler is set/unset with the MouseDown and MouseUp events to capture mouse moves when drawing } procedure ImageControl1MouseMove(Sender: TObject; Shift: TShiftState; X, Y: Single); procedure FormCreate(Sender: TObject); private FSaveBitmap: TBitmap; p1, p2: TPointF; { Start and end points of lines to draw } end; var LineDrawForm: TLineDrawForm; implementation {$R *.fmx} procedure TLineDrawForm.FormCreate(Sender: TObject); begin Image1.Bitmap.Create(Round(Image1.Width), Round(Image1.Height)); end; procedure TLineDrawForm.Image1MouseDown(Sender: TObject; Button: TMouseButton; Shift: TShiftState; X, Y: Single); begin p1.X := X; p1.Y := Y; lX.Text := FloatToStr(X); lY.Text := FloatToStr(Y); FSaveBitmap := TBitmap.Create(Image1.Bitmap.Width, Image1.Bitmap.Height); FSaveBitmap.Assign(Image1.Bitmap); { Save the current canvas as bitmap } Image1.OnMouseMove := ImageControl1MouseMove; { Activate the MouseMove event handler} end; procedure TLineDrawForm.ImageControl1MouseMove(Sender: TObject; Shift: TShiftState; X, Y: Single); begin p2.X := X; p2.Y := Y; lX.Text := FloatToStr(X); lY.Text := FloatToStr(Y); Image1.Bitmap.Assign(FSaveBitmap); Image1.Bitmap.Canvas.BeginScene; try Image1.Bitmap.Canvas.Stroke.Color := claGray; Image1.Bitmap.Canvas.StrokeThickness := 0.5; Image1.Bitmap.Canvas.DrawLine(p1, p2, 1.0); finally Image1.Bitmap.Canvas.EndScene; Image1.Bitmap.BitmapChanged; end; end; procedure TLineDrawForm.Image1MouseUp(Sender: TObject; Button: TMouseButton; Shift: TShiftState; X, Y: Single); begin p2.X := X; p2.Y := Y; lX.Text := FloatToStr(X); lY.Text := FloatToStr(Y); Image1.Bitmap.Canvas.BeginScene; try Image1.Bitmap.Canvas.Stroke.Color := claBlack; Image1.Bitmap.Canvas.StrokeThickness := 2; Image1.Bitmap.Canvas.DrawLine(P1, P2, 1.0); finally Image1.Bitmap.Canvas.EndScene; Image1.Bitmap.BitmapChanged; end; (Sender as TControl).OnMouseMove := nil; if FSaveBitmap &lt;&gt; nil then FSaveBitmap.Free; end; end. </code></pre> <p>The FMX file (LineDrawFormUnit.fmx):</p> <pre><code>object LineDrawForm: TLineDrawForm Left = 0 Top = 0 Caption = 'Polygon Form' ClientHeight = 513 ClientWidth = 650 Visible = False OnCreate = FormCreate StyleLookup = 'backgroundstyle' object Image1: TImageControl Align = alScale Position.Point = '(18,21)' Width = 620.000000000000000000 Height = 452.000000000000000000 OnMouseDown = Image1MouseDown OnMouseUp = Image1MouseUp TabOrder = 0 end object Panel1: TPanel Align = alBottom Position.Point = '(0,480)' Width = 650.000000000000000000 Height = 33.000000000000000000 TabOrder = 2 object Label1: TLabel Position.Point = '(16,8)' Width = 25.000000000000000000 Height = 15.000000000000000000 TabOrder = 1 Text = 'X:' end object Label2: TLabel Position.Point = '(384,8)' Width = 25.000000000000000000 Height = 15.000000000000000000 TabOrder = 2 Text = 'Y:' end object lX: TLabel Position.Point = '(32,8)' Width = 313.000000000000000000 Height = 15.000000000000000000 TabOrder = 3 Text = '0' end object lY: TLabel Position.Point = '(424,8)' Width = 209.000000000000000000 Height = 15.000000000000000000 TabOrder = 4 Text = '0' end end end </code></pre>
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    1. COP.S. I originally had forgotten to get rid of the unused PolygonUnit in the interface Uses clause, now corrected.
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    2. COImage1.Bitmap is not scaled up when Image1 is enlarged with the form. However, it is reduced in size when Image1 is shrunk with the form, and again expanded up to original size when the form is expanded. Setting an OnResize handler for the form allows adjusting size of Image1.Bitmap to match its container, but it is cleared. The bitmap shrinks and grows back to its original size when the form's size is reduced and expanded. There must be a non-lossy way to resize TBitmap without clearing its content. Otherwise, one would have to resort to using the TBitmap.ScanLine function.
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      1. POHow does Delphi XE2 Firemonkey's Align property set to alScale affect the coordinate system?
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    3. COP.S. Enlarging a bitmap would make it grainy, so it makes sense that bitmap shrinks and returns to its original size and not larger. Still need to figure out how it is internally accomplished by the framework.
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