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Multi-Threading for TBitmap, TCanvas, and TContext3D

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FireMonkey supports multi-threaded use of TBitmap, TCanvas, and TContext3D. Bitmaps can be created, used, and deleted across any thread. Drawing on a canvas or 3D context is internally serialized; that is, while the code that draws can run on any thread, and several threads can draw at the same time, internally access is serialized such that only one thread can draw on a canvas or 3D context at once.

TBitmap

TBitmap has complete multi-threading support. Instances can be created, destroyed, and modified in any thread without synchronization.

Note: You will still require normal thread synchronization if you share objects between threads, to ensure an object is not deleted while another thread is using it. Also, be cautious adding your own synchronization around bitmap access. It can cause deadlocks.

TCanvas

TCanvas and all subclasses have support for multi-threaded environments, but does not support simultaneous execution of Canvas instances. This means that when a Canvas calls BeginScene, the execution of the code inside this BeginScene...EndScene section blocks any other thread that attempts to process drawing, including drawing on other canvases.

Write BeginScene...EndScene blocks as short as possible to avoid blocking other threads.

For example, write:

for I := 0 to 10000 do
begin
  // thread work
  Canvas.BeginScene;
  try
    // drawing code
  finally
    Canvas.EndScene;
  end;
end;

Instead of:

Canvas.BeginScene;
try
  for I := 0 to 10000 do
  begin
    // thread code
    // drawing code
  end;
finally
  Canvas.EndScene;
end;

TContext3D

TContext3D has support for multi-threaded environments, but does not support simultaneous execution of Context3D instances. It has the same limitations as TCanvas.

See Also

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