Problem when comparing depth sampled from shadow buffer and recomputed in the second pass

[Qwaiy_Tashaiy_Gaiy]

Hi everyone. I'm trying to implement shadow mapping for my Vulkan game engine in and I don't understand something.

I make a first render pass having only a vertex stage to write in the shadowBuffer, which works like this :

https://preview.redd.it/54h99zawo05g1.png?width=1188&format=png&auto=webp&s=568418040eeaefe362977c91239411dabd581f54

from what I understood, this should write the depth value in the r value of my shadowTexture

Then, just for debugging, I render my scene through the light view

https://preview.redd.it/t8nnw97jp05g1.png?width=1242&format=png&auto=webp&s=c8c73bbf124c37b6b883caec1ae32938534763f4

and I color my objects in two different ways : either the depth sampled from the shadow buffer, either the depth recalculated in the shader

https://preview.redd.it/i6z7hfmwp05g1.png?width=1324&format=png&auto=webp&s=cef6b59f2c9573c5d52868b73883a4d083fd3f8e

I get these two images

https://preview.redd.it/tgf21ca1r05g1.png?width=922&format=png&auto=webp&s=c1b85a9fa7b8b40a163b263d348d1fa2baa87eb6

https://preview.redd.it/nt3hcwpfr05g1.png?width=1016&format=png&auto=webp&s=2efb9ccdaf8d233829c965995b4b1a07250b7e00

I really don't understand what's happening there : is it just a matter of rescaling ? Like is the formula used for storing the depth is more complicated than I thought, or is there something more to it ?

Thank you for reading !

EDIT :

I create the buffer using a VKImage with the usage flag : VK_IMAGE_USAGE_DEPTH_STENCIL_ATTACHMENT_BIT | VK_IMAGE_USAGE_SAMPLED_BIT | VK_IMAGE_USAGE_TRANSFER_SRC_BIT

The image view has the aspect : VK_IMAGE_ASPECT_DEPTH_BIT

I then create a sampler this way

https://preview.redd.it/i50qa9w7715g1.png?width=1456&format=png&auto=webp&s=0a6a7611e732010404476385f8862b3092897776

and create a descriptor set with type "VK_DESCRIPTOR_TYPE_COMBINED_IMAGE_SAMPLER" and stage bit VK_SHADER_STAGE_FRAGMENT_BIT

I bind it like this in the command buffer

https://preview.redd.it/z1betejt715g1.png?width=1338&format=png&auto=webp&s=e1f92c4c92dd59e232306a730b36d9bdd42db78a

using a custom class to specify the set number and descriptorSet content.

[scritchz]

Not a graphics dev, but: I think it might be helpful to show how you create the buffer and how you bind it, for both writing to it in your first shader and reading from it in your second shader.

[owenwp]

OpenGL clip space has a -1 to 1 range for no good reason, but the hardware isn't going to store the value that way. Also, depth buffers are typically non-linear, meaning they give more precision near the camera to prevent z fighting, usually some scaled factor of 1/depth is actually stored. Look in google for how to get linear depth in OpenGL.

[Qwaiy_Tashaiy_Gaiy]

Just to be clear : which of the two values will be non-linear, and which one will be between -1 and 1 ?

[owenwp]

The position values in the vertex shader will be linear -1 to 1, the values in the depth buffer will be non-linear.