如何以较低的分辨率渲染SceneKit着色器？

// 创建一个自定义的渲染目标
let lowResolutionSize = CGSize(width: 320, height: 240)
let lowResolutionTexture = MTLTextureDescriptor.texture2DDescriptor(pixelFormat: .rgba8Unorm, width: Int(lowResolutionSize.width), height: Int(lowResolutionSize.height), mipmapped: false)
let lowResolutionRenderTarget = device.makeTexture(descriptor: lowResolutionTexture)

// 创建一个自定义的着色器
let shader = """
    #pragma arguments
    texture2d<float, access::read> colorTexture;
    #pragma body
    constexpr sampler colorSampler(mip_filter::nearest, mag_filter::nearest);
    float4 color = colorTexture.sample(colorSampler, _surface.diffuseTexcoord);
    _surface.diffuse = color.rgb;
"""

// 创建一个自定义的SCNTechnique
let technique = SCNTechnique()
technique.fragmentFunctionName = "customShader"
technique.setValue(shader, forKey: "customShader")

// 将自定义的着色器与节点相关联
let material = SCNMaterial()
material.technique = technique
node.geometry?.materials = [material]

// 将自定义的SCNTechnique设置为场景的technique属性
sceneView.technique = technique