How do I save depth buffer to a texture with Metal?

Question

I'd like to save a depth buffer to a texture in metal, but nothing I've tried seems to work.

_renderPassDesc.colorAttachments[1].clearColor = MTLClearColorMake(0.f, 0.f, 0.f, 1.f);
[self createTextureFor:_renderPassDesc.colorAttachments[1]
                  size:screenSize
            withDevice:_device
                format:MTLPixelFormatRGBA16Float];

_renderPassDesc.depthAttachment.loadAction = MTLLoadActionClear;
_renderPassDesc.depthAttachment.storeAction = MTLStoreActionStore;
_renderPassDesc.depthAttachment.texture = self.depthTexture;
_renderPassDesc.depthAttachment.clearDepth = 1.0;   

When I pass depthTexture into my shader (which works fine with data from my other textures), all I get is red pixels.

As I change clearDepth to values closer to zero, I get darker shades of red. Perhaps I'm somehow not sampling the texture correctly in my shader?

fragment float4 cubeFrag(ColorInOut in [[stage_in]],
                     texture2d<float> albedo [[ texture(0) ]],
                     texture2d<float> normals [[ texture(1) ]],
                     texture2d<float> albedo2 [[ texture(2) ]],
                     texture2d<float> normals2 [[ texture(3) ]],
                     texture2d<float> lightData [[ texture(4) ]],
                     texture2d<float> depth [[ texture(5) ]])
{
    constexpr sampler texSampler(min_filter::linear, mag_filter::linear);
    return depth.sample(texSampler, in.texCoord).rgba;
}

Answer 1

Use depth2d<float> instead of texture2d<float> as the argument type, and read a float from the depth texture float val = depth.sample(texSampler, in.texCoord);

Answer 2

OK, it turns out that I just needed to use depth2d instead of texture2d:

depth2d<float> depth [[ texture(5) ]])