Is there a working example for Fog post effect for non AR game?

i can read the depth and mix it with the rendered image and get a linear fog effect but I can't get a true radial fog. I've been going back and forth with gemini and chatgpt and neither can do it. gemini got me a radial gradient but it's jsut projected flat across all 3d objects.

it's been all day trial after trial

this is what gives me the flat radial gradient

using namespace metal;

struct DepthFogEffectConstants {
	float4 fogColor;
	float density;
	// We no longer need the inverse projection matrix here!
};

kernel void depthFogKernel(
	texture2d<half, access::read>   inColor   [[texture(0)]],
	texture2d<float, access::read>  inDepth   [[texture(1)]],
	texture2d<half, access::write>  outColor  [[texture(2)]],
	constant DepthFogEffectConstants& uniforms [[buffer(0)]],
	uint2                           gid       [[thread_position_in_grid]])
{
	float w = outColor.get_width();
	float h = outColor.get_height();

	if (gid.x >= w || gid.y >= h) {
		return;
	}

	half4 originalColor = inColor.read(gid);
	float rawDepth = inDepth.read(gid).r;

	// 1. Guard check for empty backgrounds/skyboxes
	if (rawDepth <= 0.00001f || rawDepth >= 0.9999f) {
		outColor.write(originalColor, gid);
		return;
	}

	// 2. Map screen pixels from the center of the lens (-1.0 to 1.0)
	float2 screenPos = float2(
		((float(gid.x) / w) * 2.0f) - 1.0f,
		1.0f - ((float(gid.y) / h) * 2.0f)
	);

	// 3. Since rawDepth is already acting as a view-space Z proxy,
	// we use it to calculate the true spherical ray distance from the lens center.
	// The hypotenuse of screen offset (X, Y) and depth (Z) gives the radial distance.
	float radialDistance = sqrt(screenPos.x * screenPos.x + screenPos.y * screenPos.y + rawDepth * rawDepth);

	// 4. Calculate exponential fog matching your visual test
	float fogFactor32 = exp(-radialDistance * uniforms.density);
	half fogFactor = half(clamp(fogFactor32, 0.0f, 1.0f));
	half4 fogColor = half4(uniforms.fogColor);

	// Mix and write colors out cleanly
	half4 finalColor = mix(fogColor, originalColor, fogFactor);
	outColor.write(radialDistance, gid);
}

in this code i'm just outputing the radial distance to see that calculation and it's just wrong. i don't know what to do anymore