使用鼠標在C＃中繪制矩形

Question

我只是想在鼠標移動事件上繪制一個矩形。 我只是在MouseDown事件中保存了起點，而終點是Mouse Move中的終點。 並稱為paintImage函數。

Rectangle rec = new Rectangle (x1,y1,x2 - x1 , y2 - y1);
G.DrawRectangle(Pens.Blue,rec);

Starting Points = (x1,y1)
Ending Points = (x2,y2)

問題是，當x2的值小於x1或y2小於y1時，則矩形未繪制。

Answer 1

您可以輕松地寫一張支票：

int drawX, drawY, width, height;
if (x1 < x2)
{
    drawX = x1;
    width = x2 - x1;
}
else
{
    drawX = x2;
    width = x1 - x2;
}

if (y1 < y2)
{
    drawY = y1;
    height = y2 - y1;
}
else
{
    drawY = y2;
    height = y1 - y2;
}

Rectangle rec = new Rectangle (drawX, drawY, width, height);
G.DrawRectangle(Pens.Blue,rec);

這也可以寫成較短的形式：

Rectangle rec = new Rectangle ((x1 < x2) ? x1 : x2, (y1 < y2) ? y1 : y2, (x1 < x2) ? x2 - x1 : x1 - x2, (y1 < y2) ? y2 - y1 : y1 - y2);
G.DrawRectangle(Pens.Blue,rec);

Answer 2

如果寬度變為負數，則需要交換坐標：

int xpos = (x2-x1 < x1) ? x2 : x1;
int ypos = (y2-y1 < y1) ? y2 : y1;
int width = Math.Abs(x2-x1);
int height = Math.Abs(y2-y1);

G.DrawRectangle(Pens.Blue, new Rectangle(xpos, ypos, width, height));