Animation: Rotate a string with a timer.

ddanbe 2 Tallied Votes 1K Views Share

Start a new Forms application. Drop a Panel and a Timer control on it. Set up a Timer_Tick, Form_Load and a Panel_Paint eventhandler and fill in the code. Run the app and watch the string rotate.

using System;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Windows.Forms;

namespace StringRotation
    public partial class Form1 : Form
        public Form1()
        string RotaStr = "123";         // The string to rotate
        float RotationAngle = 0f;       // The "amount" of rotation
        Point loc = new Point(50, 50);  // Where we first start to draw the string

        private void DrawIt(Graphics G)
            const int cFontSize = 36;

            // Don't make the chars look edgy
                G.SmoothingMode = SmoothingMode.AntiAlias; 
            // Set up string stuff
                FontFamily family = new FontFamily("Arial");
                int fontStyle = (int)FontStyle.Bold;
                int emSize = family.GetEmHeight(FontStyle.Bold) / cFontSize;
                Point origin = loc;
                StringFormat format = StringFormat.GenericDefault;
                Size TxSz = TextRenderer.MeasureText(RotaStr, new Font(family, cFontSize));
            // Define rotation matrix
                Matrix RotationTransform = new Matrix(1, 0, 0, 1, 1, 1); 
            // Calculate rotation point
                PointF RotationPoint = new PointF(loc.X + TxSz.Width / 2, loc.Y + TxSz.Height / 2);          
            // Set up the path
                GraphicsPath gp = new GraphicsPath();                 
            // Add the string to the path.
                gp.AddString(RotaStr, family, fontStyle, emSize, origin, format);
            // Make the rotation transformation
                RotationTransform.RotateAt(RotationAngle, RotationPoint);
            // Color the path and fill it
                SolidBrush B = new SolidBrush(Color.OliveDrab);
                G.FillPath(B, gp);

        private void timer1_Tick(object sender, EventArgs e)
            RotationAngle += 20f; // Rotate by 20 degrees every tick
            if (RotationAngle == 360f) RotationAngle = 0f;

        private void Form1_Load(object sender, EventArgs e)
            this.timer1.Interval = 200;

        private void panel1_Paint(object sender, PaintEventArgs e)
DdoubleD 315 Posting Shark

Fun stuff man! I don't know if it is illusion or what, but does the center (pivot point) move as it rotates?

ddanbe 2,724 Professional Procrastinator Featured Poster

Yes it does! Because it is as close I can get to the center with the calculations I'm using. String measurement is a strange beast as long as you not fully understand it, as I do:( Not that I find it of the uttermost importance but if you or anyone else could give me a clue of what is still wrong here, that would be greatly appreciated!
It has to do with coordinate systems in some way, but I don't seem to get a grasp of it.

Diamonddrake 397 Master Poster

that's really neat danny. Idk when i might ever need it. But I'll add it to my private code snippet library just in case. right next to that numbers only with 1 decimal point only textbox class.

ddanbe 2,724 Professional Procrastinator Featured Poster

Thanks for your comment Diamonddrake:)
In case you are wondering why I needed it, I'm working on a combinatorics calculator. To illustrate this dry math stuff I saw a picture once on the net and would like to imitate that in C#, it is a set of 3 numbered balls. I managed to do it, but to fake the impression that these balls were rolling, I needed rotated digits.
My app is still under contruction, but I can show you my result in the attachement. I just reworked my code a bit and turned it into a snippet.

Diamonddrake 397 Master Poster

That is a good use for it! thanks for sharing!

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