在 XNA 中绘制椭圆 [英] Draw an Ellipse in XNA

问题描述

我正在尝试编写代码以在 XNA 中绘制椭圆.假设我们有以下参数:

I'm trying to write a code to draw an ellipse in XNA. Suppose we have the following parameters:

1. 半长轴 (a).
2. 半短轴 (b).
3. 椭圆中心 (h,k).
4. 和 2D 旋转 (theta).

如何使用上述参数绘制椭圆.

How it possible to draw the ellipse using the above parameters.

这是函数

public VertexPositionColor Set2dEllipse(int x, int y, int z, Color color)
{
    VertexPositionColor vertices= new VertexPositionColor[100];
    for(int i= 0;i<100;i++)
    {
        double angle = (i / 100 * Math.PI * 2);
        vertices[i].Position = New Vector3((x + (Math.Cos(angle)) * size.Width), (y + Math.Sin(angle) * size.Height), z);
        vertices[i].Color = color;
    }
}

推荐答案

我修改了取自 此处 满足您的要求.

I've modified the code taken from here to meet your requirements.

public void CreateEllipse(int a, int b, int h, int k, float theta)
{
    VertexPositionColor[] vertices = new VertexPositionColor[vertexCount];
    //Drawing an Ellipse with its major axis parallel to the x-axis. Rotation can be applied to change this.
    Vector3 position;
    const float max = MathHelper.Pi;
    //2 * max since we're moving from -Pi to +Pi in the loop.
    float step = 2 * max / (float)vertexCount;
    int i = 0;
    //Optional Axis and angle rotation for the ellipse (See later notes):
    //Vector3 axis = new Vector3(0, 0, -1);
    float angle = MathHelper.ToRadians(theta);

    for (float t = -max; t <= max; t += step)
    {
        //Formula shamelessly taken from wikipedia
        position = new Vector3(h + a * (float)Math.Cos((double)t), k + b * (float)Math.Sin((double)t), 0f);
        //Optional Rotation for the Ellipse:
        //position = Vector3.Transform(position, Matrix.CreateFromAxisAngle(axis, angle));
        vertices[i] = new VertexPositionColor(position, Color.DarkOrange);
        i++;
    }
    //Optional Rotation for the Ellipse:
    position = Vector3.Transform(position, Matrix.CreateFromAxisAngle(axis, angle));
    //then add the first vector again so it's a complete loop (sounds familiar)
    position = new Vector3(h + a * (float)Math.Cos((double)-max), k + b * (float)Math.Sin((double)-max), 0f);
    vertices[vertexCount - 1] = new VertexPositionColor(position, Color.DarkOrange);

    vertexBuffer = new VertexBuffer(device, vertexCount * VertexPositionColor.SizeInBytes,
        BufferUsage.WriteOnly);
    vertexBuffer.SetData<VertexPositionColor>(vertices);
}

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