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Asked: 2025-06-09T06:14:14+05:30

What is the correct method in HLSL for writing a pixel shader that outputs only depth information without using SV_TARGET?

I’ve been experimenting with HLSL for a little while and I’ve hit a bit of a snag that I can’t quite figure out. I’m trying to write a pixel shader that only outputs depth information, but I’m not sure how to do this without using `SV_TARGET`. I’ve read about depth-only rendering, but the examples I’ve found typically still reference `SV_TARGET`, and that’s not really what I want.

Here’s a quick rundown of what I’ve got so far. In my rendering setup, I’m specifically directing the rendering output to a depth stencil buffer, like this:

“`cpp
commandList->OMSetRenderTargets(0, nullptr, FALSE, &m_mainDepthStencilDescriptorHandle.getCpuHandle());
“`

This tells the command list not to expect any color data, as I’m only interested in writing to the depth buffer. However, the pixel shader I initially wrote looks like this:

“`hlsl
struct VS_OUTPUT
{
float4 position: SV_POSITION;
};

float4 main(VS_OUTPUT input) : SV_TARGET
{
return float4(0.0f, 0.0f, 0.0f, 0.0f);
}
“`

I know this shader has `SV_TARGET` in it, which is typically used for color outputs, but that’s not what I’m looking to do since I don’t need any color data. Instead of outputting color values, I want to ensure that depth information gets written correctly.

So, here’s where I’m stuck: what’s the proper way in HLSL to tell the shader that I’m only concerned with writing depth? Do I just need to modify the return type or the output semantics to make it clear that I’m only working with depth? I’ve come across a couple of things regarding the use of `SV_DEPTH`, but I’m not entirely sure how to integrate that into my setup.

Anyone out there have experience with this kind of thing? How can I make my pixel shader effectively output only depth without referencing the tradition `SV_TARGET`? Any examples or insights would really help me wrap my head around this. Thanks!

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    2 Answers

    1. To write a pixel shader that outputs depth information only, you can modify your pixel shader to explicitly output the depth value using the SV_DEPTH semantic. Specifically, your pixel shader function should return a single float, annotated with the semantic SV_DEPTH, instead of returning a float4 value with SV_TARGET. For instance:

      struct VS_OUTPUT
{
    float4 position : SV_POSITION;
};

float main(VS_OUTPUT input) : SV_DEPTH
{
    // Return the depth value based on the pixel's Z component after perspective division
    return input.position.z / input.position.w;
}

      This adjustment clearly communicates to Direct3D that you’re solely intending to output depth information without any associated color data. Since your render target is set up with no color target bindings (OMSetRenderTargets(0, nullptr, ...)), the use of SV_DEPTH in your pixel shader aligns with your rendering configuration. This change effectively removes any reliance on the SV_TARGET semantic and ensures correct depth-only rendering behavior.

    2. It sounds like you’re on the right track wanting to output depth information without using `SV_TARGET`. In your case, since you’re aiming to write to a depth stencil buffer, you can actually do this quite easily using `SV_DEPTH`.

      In DirectX, the pixel shader can utilize the `SV_DEPTH` semantic to specify that it will write to the depth buffer directly. You can modify your pixel shader like this:

      
struct VS_OUTPUT
{
    float4 position: SV_POSITION;
};

float main(VS_OUTPUT input) : SV_DEPTH
{
    // Assuming you have a way to calculate the depth value here
    float depthValue = input.position.z; // Example: just using the z position as depth
    return depthValue;
}

      In this version, you’re returning a float value for depth instead of a color value. The value returned by the shader will correspond to the depth that gets written to the depth stencil buffer.

      Also, ensure that in your rasterizer state setup, you’re allowing depth writing and that your depth stencil view is correctly set to handle this output. You might want to check your pixel shader compilation settings to ensure they match your intentions for depth-only rendering.

      Give this a try, and it should help you focus just on writing depth values!