在金属上绘制圆/半圆

Question

我是金属新手。我想画一个半圆。任何想法或建议，画一个半圆。我尝试使用tesselation

float u = patch_coord.x;
float v = patch_coord.y;
float w = patch_coord.z;




   float x = u * patchIn.control_points[0].position.x + v * patchIn.control_points[1].position.x + w * patchIn.control_points[2].position.x;
    float y = u * patchIn.control_points[0].position.y + v * patchIn.control_points[1].position.y + w * patchIn.control_points[2].position.y;

    float2 tangent = normalize(float2(x, y)) / 25;

当我始终将其标准化时，它位于屏幕中间。我想用手指触摸画一个圆圈