動作環境

C++ Builder XE4

関連 http://qiita.com/7of9/items/a5c05ddddd268d8e82e7

塗りつぶしを試す。

TCanvas.FloodFill Method

Unit1.cpp

//---------------------------------------------------------------------------

# include <vcl.h>
# pragma hdrstop

# include "Unit1.h"
//---------------------------------------------------------------------------
# pragma package(smart_init)
# pragma resource "*.dfm"
TForm1 *Form1;
//---------------------------------------------------------------------------
__fastcall TForm1::TForm1(TComponent* Owner)
	: TForm(Owner)
{
}
//---------------------------------------------------------------------------
void __fastcall TForm1::Button1Click(TObject *Sender)
{
	TRect R = GetClientRect();
	//            X1      Y1     X2       Y2        X3       Y3     X4      Y4
	Canvas->Chord(R.Left, R.Top, R.Right, R.Bottom, R.Right, R.Top, R.Left, R.Top);

	Canvas->Brush->Color = clBlue;

	long hormid = (R.Left + R.Right) / 2;
	Canvas->FloodFill(hormid, R.top - 100, clBlack, fsBorder);

}
//---------------------------------------------------------------------------

ボタンを2回押さないと中の色を塗らない
他のウィンドウで隠された後、描画されない

参考 http://stackoverflow.com/questions/24931706/how-to-repaint-canvas-just-in-time

描画をきちんとするにはFormPaint()で実装するようだ。

Unit1.cpp

//---------------------------------------------------------------------------

# include <vcl.h>
# pragma hdrstop

# include "Unit1.h"
//---------------------------------------------------------------------------
# pragma package(smart_init)
# pragma resource "*.dfm"
TForm1 *Form1;
//---------------------------------------------------------------------------
__fastcall TForm1::TForm1(TComponent* Owner)
	: TForm(Owner)
{
}
//---------------------------------------------------------------------------
void __fastcall TForm1::FormPaint(TObject *Sender)
{
	TRect R = GetClientRect();
	//            X1      Y1     X2       Y2        X3       Y3     X4      Y4
	Canvas->Chord(R.Left, R.Top, R.Right, R.Bottom, R.Right, R.Top, R.Left, R.Top);

	Canvas->Brush->Color = clBlue;

	long hormid = (R.Left + R.Right) / 2;
	Canvas->FloodFill(hormid, R.Top + 50, clBlack, fsBorder);
}
//---------------------------------------------------------------------------

こちらでは、他のウィンドウで隠してから表示してもきちんと描画される。