IOS金属：锯齿抗锯齿

我试着画一个半圆，用的是渲染编码器的绘图索引

[renderEncoder setVertexBuffer:self.vertexBuffer offset:0 atIndex:0];

[renderEncoder drawIndexedPrimitives:MTLPrimitiveTypeTriangleStrip
                              indexCount:self.indexCount
                               indexType:MTLIndexTypeUInt16
                             indexBuffer:self.indicesBuffer
                       indexBufferOffset:0];

其中，通过计算创建了圆的顶点缓冲和指示缓冲。

int segments = 10;


float vertices02[ (segments +1)* (3+4)];
vertices02[0] = centerX;
vertices02[1] = centerY;
vertices02[2] = 0;

//3, 4, 5, 6 are RGBA
vertices02[3] = 1.0;
vertices02[4] = 0;
vertices02[5] = 0.0;
vertices02[6] = 1.0;    

uint16_t indices[(segments -1)*3];

for (int i = 1; i <= segments ; i++){
    float degree = (i -1) * (endDegree - startDegree)/ (segments -1) + startDegree;

    vertices02[i*7] = (centerX + cos([self degreesToRadians:degree])*radius);
    vertices02[i*7 +1] = (centerY +  sin([self degreesToRadians:degree])*radius);
    vertices02[i*7 +2] = 0;

    vertices02[i*7 +3] = 1.0;
    vertices02[i*7 +4] = 0;
    vertices02[i*7 +5] = 0.0;
    vertices02[i*7 +6] = 1.0;

    if (i < segments){
        indices[(i-1)*3 + 0] = 0;
        indices[(i-1)*3 + 1] = i;
        indices[(i-1)*3 + 2] = i+1;
    }
}

所以我把9个三角形组合成一个180度的圆。

然后创建顶点缓存器和指示缓冲区。

self.vertexBuffer = [device newBufferWithBytes:vertexArrayPtr
                                            length:vertexDataSize
                                           options:MTLResourceOptionCPUCacheModeDefault];
self.indicesBuffer = [device newBufferWithBytes:indexArrayPtr
                                             length:indicesDataSize 
                                            options:MTLResourceOptionCPUCacheModeDefault];

结果如下：

https://i.stack.imgur.com/yVscr.png

我相信这是iOS金属公司的反混叠问题。我曾经用同样的技术在OpenGL中创建半圆，但是边缘更平滑。

有什么建议来解决这个问题吗？