[求助]解释下这下语句

Copies a portion of a bitmap onto a rectangle on the canvas, replacing one of the colors of the bitmap with the brush of the canvas.

Delphi syntax:

procedure BrushCopy(const Dest: TRect; Bitmap: TBitmap; const Source: TRect; Color: TColor);

C++ syntax:

void __fastcall BrushCopy(const Types::TRect &Dest, TBitmap* Bitmap, const Types::TRect &Source, TColor Color);

Description

Use BrushCopy to achieve special effects such as making the copied image partially transparent. BrushCopy is provided mainly for backward compatibility. Use a TImageList instead of BrushCopy.

Dest specifies the rectangular portion of the canvas that will receive the copy of the bitmap. Bitmap specifies the graphic to copy from. Source specifies the rectangular area of Bitmap to copy. Color specifies the color in Bitmap to replace with the Brush of the canvas.

To use BrushCopy to make the copied image partially transparent, specify the color of the surface of the canvas (clBackground for example) as the Color of the Brush property, then call BrushCopy.