I created a pixmap or drawable window, then used XDrawLine() function 
drawed a line as below fingure:

		width = 300
	================================
	|				|
	|				|
	|			p1	|
	|			\	|
	|			 \	| height = 300
	|			  \	|
	|			   \	|
	|			    \	|
	|			     \	|
	|			      \	|
	|			       \|p3
	|				| 
	|===============================| \
					    \
					     p2

	I created the pixmap or drawable window only with size 300x300.
But I draw line from p1(x1=270,y1=100) to p2(x2=500,y2=800).
My question is, dose the XDrawLine function can finger out that correct
p3(x3 and y3) for me? If you calculate x3 and y3. 

x3 = 300;

@ = art tan (( 800 - 100)/(500 - 270)) = 71.81 degrees;

y3 = 100 + x3/tan(@) = 100 + 300/tan(71.81) = 198.58 ~= (integer) 199.

How do I prove XDrawLine() give me the right x3, y3 or not?
Please don't ask me why I don't created a 900x900 pixmap. No, I don't
wan to. 

Thanks in advance!