用OpenGL或D3D绘制Ellipse的有效方法 [英] Effecient way to draw Ellipse with OpenGL or D3D

问题描述

  void DrawCircle（float cx，float cy，float r，int num_segments）
 {
 float theta = 2 * 3.1415926 / float（num_segments）; 
 float c = cosf（theta）; //预先计算正弦和余弦
 float s = sinf（theta）; 
 float t; 
 
 float x = r; //我们从角度= 0开始
 float y = 0; 
 
 glBegin（GL_LINE_LOOP）; 
 for（int ii = 0; ii  {
 glVertex2f（x + cx，y + cy）; //输出顶点
 
 //应用旋转矩阵
t = x; 
 x = c * x  -  s * y; 
 y = s * t + c * y; 
} 
 glEnd（）; 
 
 
 
 
 
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我想知道是否有类似的方法来绘制椭圆的主要/短轴矢量和大小都是已知的。
解决方案
 
无法在openGL中绘制曲线，只需很多直线线。但是如果你使用了顶点缓冲对象，那么你不必将每个顶点都发送到显卡上，这样会更快。
  b 
 $ b 
 我的Java示例 
 
There is a fast way to draw circle like this
void DrawCircle(float cx, float cy, float r, int num_segments) 
{ 
    float theta = 2 * 3.1415926 / float(num_segments); 
    float c = cosf(theta);//precalculate the sine and cosine
    float s = sinf(theta);
    float t;

    float x = r;//we start at angle = 0 
    float y = 0; 

    glBegin(GL_LINE_LOOP); 
    for(int ii = 0; ii < num_segments; ii++) 
    { 
        glVertex2f(x + cx, y + cy);//output vertex 

        //apply the rotation matrix
        t = x;
        x = c * x - s * y;
        y = s * t + c * y;
    } 
    glEnd(); 
}
I am wondering if there is a similar way to draw ellipse where its major/minor axes vector and size are both known.
解决方案
There is no way to draw a curve in openGL, just a lot of straight lines.  But if you used vertex buffer objects then you won't have to send each vertex to the graphics card which will be much faster.

My Java Example

                        
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