求内切圆的圆心和半径（已知三个点的坐标）

转自:http://blog.csdn.net/baidu_31872269/article/details/54923589

/******
m0 n0 m1 n1 m2 n2 为三角形的三个点的坐标值 m为横坐标 n为纵坐标
px 内切圆的圆心的横坐标
py 内切圆的圆心的纵坐标
pr 内切圆的半径

***/

int NeiQieYuan(int m0, int n0, int m1, int n1, int m2, int n2, float *px, float *py, float *pr)
{
int dax = 0;
int day = 0;

int dbx = 0;
int dby = 0;

float absA = 0.0f;
float absB = 0.0f;
float temp = 0;

dax = m0 - m1;
day = n0 - n1;

dbx = m2 - m1;
dby = n2 - n1;

temp = dax * dax + day * day * 1.0f;
absA = sqrtf(temp);
temp = dbx * dbx + dby * dby * 1.0f;
absB = sqrtf(temp);

// (absB * day - absA * dby)(y - n1) = (absA * dbx - absB * dax)(x - m1)

// 第一个角平分线方程
// a(y - n1) = b(x - m1)

// 方程1
float a = 0.0f;
float b = 0.0f;

a = (absB * day - absA * dby);
b = (absA * dbx - absB * dax);

dax = m0 - m2;
day = n0 - n2;

dbx = m1 - m2;
dby = n1 - n2;

temp = dax * dax + day * day * 1.0f;
absA = sqrtf(temp);
temp = dbx * dbx + dby * dby * 1.0f;
absB = sqrtf(temp);

float c = 0.0f;
float d = 0.0f;

c = (absB * day - absA * dby);
d = (absA * dbx - absB * dax);
// 第二个角平分线方程
// c(y - n2) = d(x - m2)
float PointX = 0.0f;
float PointY = 0.0f;

if(a != 0)
{
PointX = (c * b * m1 + n2 * a * c - n1 * a * c - a * d * m2) / (c * b - a * d);
PointY = b * (PointX - m1) / a + n1;

}else
{
PointX = m1;
PointY = d * (m1 - m2) / c + n2;
}

// dax * (y - n2) = day * (x - m2)

// 点到直线的方程 (-day)(y - PointY) = (dax)(x - PointX)

// 计算点到直线的距离

float intersectionX = 0.0f;
float intersectionY = 0.0f;

if(dax != 0)
{
intersectionX = (day * day * m2 - day * dax * n2 + day * dax * PointY + dax * dax * PointX) / (dax * dax + day * day);
intersectionY = day * (intersectionX - m2) / dax + n2;

}else
{
intersectionX = m2;
intersectionY = dax * (intersectionX - PointX) / (-day) + PointY;
}

*px = PointX;
*py = PointY;

float temp1 = (intersectionX - PointX) * (intersectionX - PointX) + (intersectionY - PointY) * (intersectionY - PointY);
*pr = sqrtf((intersectionX - PointX) * (intersectionX - PointX) + (intersectionY - PointY) * (intersectionY - PointY));

return 0;

}

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