most recent 30 from stackoverflow.com 2025-08-07T12:07:18Z https://stackoverflow.com/feeds/question/8336127 https://creativecommons.org/licenses/by-sa/4.0/rdf https://stackoverflow.com/q/8336127 4 Shannon Matthews https://stackoverflow.com/users/395461 2025-08-07T03:15:45Z 2025-08-07T00:49:14Z

<p><strong>Background</strong></p> <p>I/m building a custom FireMonkey GUI control. I want to render the control to a back buffer. The back buffer will be drawn on the control's canvas.</p> <ul> <li><p>The back buffer is a Fmx.TBitmap object.</p></li> <li><p>I am using a back buffer because the control rendering code is a little involved and does not need to be called each time the control is repainted. The back buffer will only be updated when some control properties change. </p></li> </ul> <p><strong>Problem</strong></p> <p>The BackBuffer.Canvas drawing operations have no visible effect. However clearing the bitmap, or setting the value of the bitmap pixels individually do work as expected. </p> <p>For some reason the BackBuffer.Canvas object will not draw on the back buffer bitmap. </p> <ul> <li>I think I've set the required Canvas.Fill properties correctly. </li> <li>All the canvas properties I've checked appear to be correct. (Canvas width/height/etc)</li> </ul> <p>I've extracted the relevant code in case that contains some clues. </p> <pre><code>TMyControl(TControl) private protected BackBuffer : TBitmap; procedure Paint; override; procedure Resize; override; public constructor Create(AOwner: TComponent); override; end; constructor TMyControl.Create(AOwner: TComponent); begin inherited; BackBuffer := TBitmap.Create(10, 10); end; procedure TFxSampleDisplay.Resize; var w, h : integer; begin inherited; // Ensure BackBuffer is the same size as the control. w := round(BoundsRect.Width); h := round(BoundsRect.Height); BackBuffer.SetSize(w,h); end; procedure TMyControl.Paint; var r : TRectF; begin inherited; //******** This has visible results ******** BackBuffer.Clear($1100ff00); // Fill with semi-opaque green background BackBuffer.Pixels[2,2] := $ffff0000; // Draw a red pixel //******** This doesn't have visible results ******** r.Left := 0; r.Top := 0; r.Right := 50; r.Bottom := 50; BackBuffer.Canvas.Fill.Color := $ffff0000; // Set fill to RED. BackBuffer.Canvas.Fill.Kind := TBrushKind.bkSolid; BackBuffer.Canvas.FillRect(r, 10,10, AllCorners, 1); //******** Draw the backbuffer on to the controls canvas ******** Canvas.DrawBitmap(BackBuffer, BoundsRect, BoundsRect, 1); end; </code></pre>

https://stackoverflow.com/questions/8336127/-/8338771#8338771 4 Kromster https://stackoverflow.com/users/77764 2025-08-07T09:05:44Z 2025-08-07T17:32:39Z

<p>Try surrounding your drawing with:</p> <pre><code>BackBuffer.Canvas.BeginScene; .. .. BackBuffer.Canvas.EndScene; BackBuffer.BitmapChanged; </code></pre> <p>P.S. I'm pretty new with FireMonkey style, so just try it out and write if it worked please!</p>

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