CODEWITHSUNDEEP
c++algorithmgeometry
jmasterx
jmasterx

Reputation: 54103

Finding angle rectangle will occupy when drawn along circle (see drawing)

Here is what I'm trying to do. I have a font that is basically bitmap rectangles for each glyph. I'm trying to get arced text effect like this:

enter image description here

My plan is, given a center and a radius, I'm going to solve for the position and angle of each glyph.

I have a function that can find the position:

Vec2 Math::positionFromCenterToLineAt( Vec2 center, float dist,
        float totalAngular, float angularDistance, float angularOffset )
    {
        float startAngle = -((totalAngular) / 2.0f);
        float curAngle = startAngle + angularDistance;
        curAngle -= angularOffset;
        curAngle += angularDistance / 2.0f;
        curAngle += CGE_PI;

        Vec2 retVec = center;
        Vec2 angVec = Vec2(sin(curAngle),cos(curAngle));
        angVec *= dist;
        retVec += angVec;

        return retVec;
    }

It requires me to know how much of the circle will be occupied in radians, and requires how many degrees from the start angle the current glyph should be drawn at.

What I cannot figure out is a function to find the angle a given glyph will occupy given the radius, center, and width and height of the glyph. Each glyph can have a different dimension.

See this: enter image description here

As you can see, I'm looking for in radians, that sector of the circle.

How could I calculate it?

Thanks

Upvotes: 2

Views: 357

Answers (1)

huseyin tugrul buyukisik
huseyin tugrul buyukisik

Reputation: 11910

2*pi*radius equals the circumference
You know radius as a pixel base(lets say it is 40 pixels)
You can find circumference(lets say it is 251 pixels)
Then, if you get width of a char(lets say it is 8)
You know the angle of arc: angle=2*pi*(8/251)=2*pi*0.03=0.2 radians
0.2 radians * 57.3 = 11.5 degrees

How to find width of a char according to current font?

LOGFONT lf;
int width=lf.lfWidth; //beware! this is average

You want precise option?

GetTextExtentPoint32() // search usage of this!

Its structure type is:

 BOOL GetTextExtentPoint32(
  __in   HDC hdc,
  __in   LPCTSTR lpString,
  __in   int c,
  __out  LPSIZE lpSize
);

Upvotes: 2

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