Question

Help explaining some Trigonometry on my C# method

Asked by: stormist

I have C# method, the relevant code is below. It draws the border around a clock.
I need help understanding this part mathematically:
 float x = (float)(_CenterX / _PI) - (this.Width / (125));
            float y = (float)(_CenterY / _PI) - (this.Width / (125));

What would be the purpose of dividing the center of a circle X cord or Y cord by PI?

Any theories as to why this method breaks down when the user decreases the width enough? (the circle this method draws gets off center with the rest of the renderings (a clock)

float x = (float)(_CenterX / _PI) - (this.Width / (125));
            float y = (float)(_CenterY / _PI) - (this.Width / (125));
 
            float width = ((this.ClientSize.Width / 2) - penWidth) + _hourLength;
            float height = ((this.ClientSize.Height / 2) - penWidth) + _hourLength;
 
            Rectangle rect = new Rectangle((int)x, (int)y, (int)width, (int)height);
graphics.FillEllipse(gradientBrush, rect);

                                  
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Asked On
2009-09-16 at 22:40:32ID24738800
Topics

Math & Science

,

Algorithms

Participating Experts
2
Points
500
Comments
3

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Answers

 

by: InteractiveMindPosted on 2009-09-17 at 03:35:55ID: 25354504

It all looks pretty unnecessary. If I understand your situation, would something like this not work?

int radius = this.Width/2;
Rectangle rect=new Rectangle(_CenterX-radius, _CenterY-radius, 2*radius, 2*radius);
graphics.FillEllipse(gradientBrush, rect);

                                              
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by: programmer78Posted on 2009-09-17 at 03:45:39ID: 25354553

These formulas looks like empiric. as far as I understood, (x,y,wdth,height) - is a rectangle, which surrounds ellipse (circle). The rectangle has 4 dimensions (2 coordinates and 2 sizes), in this formula these 4 parameters are functions of 6 parameters.
Any number divided by PI results in diameter of the circle, which has the perimeter that equals to number.
Such a complicated calculation may be due to they need draw something as a background and this background should be congruent to the clock.

 

by: stormistPosted on 2009-09-17 at 17:42:34ID: 25362329

Hi,
Interactive mind: the mod you suggest makes the filling about twice as big as the clock. Here are the variables that are set on the clock upon each resize:
 this.Width = this.Height;
            this._Radius = this.Height / 2;
            this._CenterX = this.ClientSize.Width / 2;
            this._CenterY = this.ClientSize.Height / 2;
            this._hourLength = (float)this.Height / 3 / 1.65F;
            this._minuteLength = (float)this.Height / 3 / 1.20F;
            this._secondLength = (float)this.Height / 3 / 1.15F;
            this._hourThickness = (float)this.Height / 60;
            this._minuteThickness = (float)this.Height / 80;
            this._secondThickness = (float)this.Height / 200;
            this._CenterCircleRadius = this.Height / 50;

any ideas on how to make the filling match the clock? Also this routine is done for the outer border of the clock: ( it is almost exact, but seems to be off when the clock is resized too small.

  float x = (float)(_CenterX / _PI) - (this.Width / 1000);
            float y = (float)(_CenterY / _PI) - (this.Width / 1000);
 
            float width = ((this.ClientSize.Width / 2) - penWidth) + _hourLength;
            float height = ((this.ClientSize.Height / 2) - penWidth) + _hourLength;
 
 graphics.DrawEllipse(pen, x, y, width, height);

                                              
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