Draw Rectangle in c# using Mouse

Question

I am just trying to draw a rectangle on mouse move event . I just saved the starting point in MouseDown Event and Ending Point is from Mouse Move . And called the paintImage Function .

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

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

The Problem is When the value of x2 is less than x1 OR y2 is less than y1 the rectangle is not drawing ... Anyone help me on this

Answer 1

You could easily write a check:

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);

This can also be written in shorter form:

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

You need to swap coordinates in case the width becomes negative:

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));