关于TImage控件的画图问题

[jone7319]

在Form1上放个Image1.想法是通过按下鼠标右键确定线条的起点A，继续按着右键不放拖动鼠标确定线条的终点B，放开鼠标右键画一条从A到B的线段。
以下是我的代码：
//---------------------------------------------------------------------------

#include <vcl.h>
#pragma hdrstop

#include "Unit1.h"
//---------------------------------------------------------------------------
#pragma package(smart_init)
#pragma resource "*.dfm"
TForm1 *Form1;
bool rmd=false;
TPoint a,b;
//---------------------------------------------------------------------------
__fastcall TForm1::TForm1(TComponent* Owner)
: TForm(Owner)
{
}
//---------------------------------------------------------------------------

void __fastcall TForm1::Image1MouseMove(TObject *Sender, TShiftState Shift,
int X, int Y)
{
if( rmd )
{
Image1->Canvas->MoveTo(a.x,a.y);
Image1->Canvas->LineTo(b.x,b.y);
b.x=X;
b.y=Y;
Image1->Canvas->MoveTo(a.x,a.y);
Image1->Canvas->LineTo(b.x,b.y);
}

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

void __fastcall TForm1::Image1MouseDown(TObject *Sender,
TMouseButton Button, TShiftState Shift, int X, int Y)
{
if(Button==1)
{
rmd=true;
a.x=X;
a.y=Y;
}

}
//---------------------------------------------------------------------------
void __fastcall TForm1::Image1MouseUp(TObject *Sender, TMouseButton Button,
TShiftState Shift, int X, int Y)
{
rmd=false;
}
//---------------------------------------------------------------------------
void __fastcall TForm1::FormCreate(TObject *Sender)
{
Image1->Canvas->Pen->Color=clRed;
Image1->Canvas->Pen->Width=3;
Image1->Canvas->Pen->Style<<psDot;
Image1->Canvas->Pen->Mode=pmXor;
}
//---------------------------------------------------------------------------

以上代码的运行结果，是每次按下鼠标会从之前的位置多画一条到当前位置的线条，结果变成画折线了，而不是多条线段，达不到要求的效果。

通过修改代码，在void __fastcall TForm1::Image1MouseDown事件中加入
Image1->Canvas->MoveTo(a.x,a.y);
Image1->Canvas->LineTo(b.x,b.y);
效果有所改观，但不理想。


修改后的完整代码如下：
//---------------------------------------------------------------------------

#include <vcl.h>
#pragma hdrstop

#include "Unit1.h"
//---------------------------------------------------------------------------
#pragma package(smart_init)
#pragma resource "*.dfm"
TForm1 *Form1;
bool rmd=false;
TPoint a,b;
//---------------------------------------------------------------------------
__fastcall TForm1::TForm1(TComponent* Owner)
: TForm(Owner)
{
}
//---------------------------------------------------------------------------

void __fastcall TForm1::Image1MouseMove(TObject *Sender, TShiftState Shift,
int X, int Y)
{
if( rmd )
{
Image1->Canvas->MoveTo(a.x,a.y);
Image1->Canvas->LineTo(b.x,b.y);
b.x=X;
b.y=Y;
Image1->Canvas->MoveTo(a.x,a.y);
Image1->Canvas->LineTo(b.x,b.y);
}

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

void __fastcall TForm1::Image1MouseDown(TObject *Sender,
TMouseButton Button, TShiftState Shift, int X, int Y)
{
if(Button==1)
{
rmd=true;
a.x=X;
a.y=Y;
Image1->Canvas->MoveTo(a.x,a.y);
Image1->Canvas->LineTo(b.x,b.y);
}

}
//---------------------------------------------------------------------------
void __fastcall TForm1::Image1MouseUp(TObject *Sender, TMouseButton Button,
TShiftState Shift, int X, int Y)
{
rmd=false;
}
//---------------------------------------------------------------------------
void __fastcall TForm1::FormCreate(TObject *Sender)
{
Image1->Canvas->Pen->Color=clRed;
Image1->Canvas->Pen->Width=3;
Image1->Canvas->Pen->Style<<psDot;
Image1->Canvas->Pen->Mode=pmXor;
}
//---------------------------------------------------------------------------


结果是得到了不同的线段，但是之前的线条还是会闪现，不是想要的结果，希望各位给个算法代码。我是弄不明白，我已用MoveTo移动了位置，为什么还会从前一个位置开始画线？

[ooolinux]

鼠标拖动过程你需要显示不断随鼠标移动的线吗？

[ooolinux]

你是用什么版本的C++ Builder？如果用C++ Builder 6.0，参考： F:\Program Files (x86)\Borland\CBuilder6\Examples\Apps\Doodle 这个自带的画图程序，你的C++ Builder 6.0可能安装在C盘，而不是像我在F盘。 __fastcall TDoodleForm::TDoodleForm(TComponent* Owner) : TForm(Owner) { DoubleBuffered=true; //原代码加一句这个可以避免闪烁 }

[jone7319]

引用 1 楼 u010165006 的回复:

鼠标拖动过程你需要显示不断随鼠标移动的线吗？

是的，但是我目前得到的效果不理想、

[jone7319]

还是弄不明白，感觉这个MouseMove事件有bug，加了个Sleep(100)延时效果好了些。 //--------------------------------------------------------------------------- void __fastcall TForm1::Image1MouseDown(TObject *Sender, TMouseButton Button, TShiftState Shift, int X, int Y) { if(Button==1) { Sleep(100); rmd=true; a.x=X; a.y=Y; Image1->Canvas->MoveTo(a.x,a.y); Image1->Canvas->LineTo(b.x,b.y); } }