TControlCanvas = class(TCanvas)
class PASCALIMPLEMENTATION TControlCanvas : public Vcl::Graphics::TCanvas
TControlCanvas is a specialized canvas object associated with a control.
TControlCanvas provides a graphics context for controls that render their own images.
Not all controls need a canvas. Many controls rely on underlying Windows screen objects to provide rendering logic.
TControlCanvas is descended from TCanvas, which provides many properties, events, and methods to aid in the creation of rich images. TControlCanvas adds properties and methods to interact with a control object, and to manage the device context associated with the control.