how do you draw a line and make it swing in a full circle while one end of it is fixed on the screen?

[tianxiao]

i tried making the program with a line fixed at one point and the line would swing in a circle. Not much success so far. any suggestions?

[Laplace's Demon]

What grade are you in? Doing this requires trigonometry.

That said, if the line itself is not important and trigonometry scares you, then you could use the procedure "drawarc". You can use this to create a small indicator at the end of an imaginary line, so it can be used to indicate values on a gauge for example.

[Tony]

To draw a line, you need to know the two points. One of the points is fixed, making that part very easy. The other point follows the circumference of a circle. What is the formula for the circle?

(Alternatively, and perhaps easier if you know the math, you could treat the line as a ray of fixed length and find it's end position using angles (via trigonometry)).

[tianxiao]

grade 10, love math, love trig.

[tianxiao]

yes but how can i put that in a program and make a full circle?

[tianxiao]

like i need one end of the line free and spinning around the other end of that line.

[Laplace's Demon]

Allright then. In trig we know that:

sin gives you the Y value on the unit circle

cos gives you the X value on the unit circle.

So you want to use the first point of the line as the origin of a circle, and keep track of an "angle" variable and use sin and cos to find the y and x values of the other end of your line. The sin and cos values will give you points on the unit circle based on your angle, you want to then multiply those values by the desired radius of your circle to find the end of your line.

Try working with that.