Canvas Issue: Drawing a line through 3 points

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  • Humm

       I have a canvas object. And...

       I was wondering myself how to draw a line depending on three points. It's compulsory that it it passes through three points due its a light ray and a prism...

       But I only see an action wich is :Draw Line from X1,Y1 to X2,Y2 ...

    �Any experience in this?

  • Use two Draw Line action. One for point A to point B and another from B to C.

  • Yes, but there is a problem with that: The line must be straight. And the points 1 and 2 are moving all time...

    Seems quite difficult...

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  • Use X1,Y1 for the actual objects that are moving?

  • x1 is constant, y1 is variable.

    x2 is variable, y2 is constant.

    The ray (represented by this line, must go further x2,y2 to the infinite.

  • Perhaps, this could be useful:

    If I want to have an X and Y whatever points in this space, I can use:

    ((X -x1)/(x2-x1))-((Y-y1)/(y2-y1))

    What do you think?

  • It works! Due to a factor: The final X is always known. The only thing left to find out is the Y. Easy!

  • You wanted to draw a straight line between 3 points ? How is it possible ? (Unless the points are aligned, but that would be the same as drawing a line between 2 points)

    Did you mean 2 points but with only 3 known coordinates ?

  • I had 2 points known. All are moving al time, like particules in a fluid. The thrird one is a wall. So I know only it's X. The only thing to find out is the Y.

    Because of that I must be careful of two moving points to obtain a straight line.

  • Oh ! And the line will always hit the wall ? Then this should do the trick :

    X1 = FirstObject.X

    Y1 = FirstObject.Y

    X2 = Wall.X

    Y2 = FirstObject.Y + Tan(Angle(FirstObject.X, FirstObject.Y, SecondObject.X, SecondObject.Y)) * abs(FirstObject.X - Wall.X)

  • That was near the solution, thanks! But for some values, the line breaks.

    The formula I have finally used and works fine is:


    Where x1,x2,y1,y2 and X are known values.

    Nevertheless, thanks a lot!

  • That's pretty much the same formula without using the angle ! <img src="smileys/smiley2.gif" border="0" align="middle" />

    Tan(angle) = (y2-y1) / (x2 - x1)

    Replacing that in my formula, we obtain the same thing ! Maybe there's something wrong with the angle() function... Nevertheless, you're better off without it !

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