Move a rectangle using angles

Question

I need to move a rectangle using angles. Actually I want to change the direction of my moving rectangle when it reaches the location I have given in my code in if statement!

I just need the way I can find out how to move my rectangle at 60, 30, 60, 120, 150, 270 degrees!

Suppose that if

          circle.Y>=this.Height-80

See this: enter image description here

I really actually need to change the direction of rectangle movement using angles! so that at certain location reaches I can change the rectangle direction according to angle of my own choice! such that:

if(circle.Y>=this.Height-80)
    move in the direction of 90 degrees

if(circle.X>=this.Width-80)
    move in the direction of 60 degree

as you can see in the screen shot!

What I have been trying is:

public partial class Form1 : Form
{
    Rectangle circle;
    double dx = 2;
    double dy = 2;

    public Form1()
    {
        InitializeComponent();
        circle = new Rectangle(10, 10, 40, 40);
    }

    private void Form1_Load(object sender, EventArgs e)
    {
        this.Refresh();
    }

    private void Form1_Paint(object sender, PaintEventArgs e)
    {
        Graphics g = e.Graphics;
        g.SmoothingMode = SmoothingMode.AntiAlias;
        g.FillEllipse(new SolidBrush(Color.Red), circle);
    }

    private void timer_Tick(object sender, EventArgs e)
    {
        circle.X += (int)dx;
        circle.Y += (int)dy;
        if (circle.Y>=this.Height-80)
        {
            dy = -Math.Acos(0) * dy/dy; //here i want to change the direction of circle at 90 degrees so that it should go up vertically straight with same speed
        }
        this.Refresh();
    }
}

The Problem is that I have been trying changing my conditions to:

dy = -Math.Asin(1) * dy;
dx = Math.Acos(0) * dx ;

but in both cases nothing is happening and the direction remains same! I just want to move the circle in inverted upward direction at 90 degrees when it reach at

circle.Y>=this.Height-80

Even if it's an assignment, we still help. It's the effort you put into the code that matters to us. — But I'm Not A Wrapper Class, Jun 02 '14 at 15:20
the answer would remain same dear see dx=dy=2; and though dx/dy=dy/dx=1; — Java Nerd, Jun 02 '14 at 15:29
@user3411946 - Don't put extra code that achieves nothing and only serves to confuse us. There is obviously no purpose to `* dy/dy`. Please change the code to reflect what you are actually trying to achieve. Or explain it in words, and we can tell you what the calculation should be. — mbeckish, Jun 02 '14 at 15:31

score 3 · Accepted Answer · answered Jun 05 '14 at 05:37

You need to draw the rectangle again to some image for it to display. I created this code for moving and drawing rectangle on pictureBox1, using your already defined circle-rectangle:

Moving the rectangle:

public void MoveRectangle(ref Rectangle rectangle, double angle, double distance)
{
   double angleRadians = (Math.PI * (angle) / 180.0);
   rectangle.X = (int)((double)rectangle.X - (Math.Cos(angleRadians) * distance));
   rectangle.Y = (int)((double)rectangle.Y - (Math.Sin(angleRadians) * distance));
}

Drawing the rectangle and displaying it in the PictureBox:

public void DrawRectangle(Rectangle rectangle)
{
   Bitmap bmp = new Bitmap(pictureBox1.Width, pictureBox1.Height);
   using (Graphics g = Graphics.FromImage(bmp))
   {
      g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.AntiAlias;
      g.FillEllipse(new SolidBrush(Color.Red), rectangle);
   }
   pictureBox1.Image = bmp;
}

Demo it with a button click:

private void Button1_Click(object sender, EventArgs e)
{
   MoveRectangle(ref circle, 90, 5);
   DrawRectangle(circle);
}

well I don't need the whole code but i got super ideas from your answer bounty awarded thanks! — Java Nerd, Jun 05 '14 at 17:20

Nicolas Castro · Answer 2 · 2014-06-02T15:46:49.327

Math.Asin(1) * dy is a constant value. Thus, you should use, for example, an instance variable that increments in each Tick of your timer.

...And *dy/dy is irrelevant.

public partial class Form1 : Form
{
    Rectangle circle;
    double dx = 2;
    double dy = 2;
    acum=0; //the new variable

...

private void timer_Tick(object sender, EventArgs e)
    {
        circle.X += (int)dx;
        circle.Y += (int)dy;
        if (circle.Y>=this.Height-300)
        {
            dy = -Math.Acos(acum); 
            acum+=1; //your accumulator
        }
        this.Refresh();
    }

score 1 · Answer 3 · answered Jun 02 '14 at 15:52

acos and asin are the inverse of sin and cos so the output of those two functions is an angle (usually in radians). This makes the code incorrect.

I strongly suggest that you read up on vector and matrix maths as using Euler angles can get quite messy.

So, you will have a position vector P and a movement vector M and the current position is:

 P' = P + M.t

where t is time, P is the original position and P' is the current position.

Then, when you want to change direction, you create a rotation matrix and multiply the movement vector M by this rotation matrix.

The advantage here is that you can step from a 2D system to a 3D system by adding a Z component to your vectors and increasing the size of your matrices.

Actually, in your example, the rotation matrix is not needed, the new movement vector will be (0,1) assuming upwards is +ve y. — Skizz, Jun 02 '14 at 15:54

Move a rectangle using angles

3 Answers3