hi guys
my set up is sort of like this with URP feature, main camera render stuff like usual.
a custom pass will render stuff with remapped depth range on top or behide the normal camera stuff, for example, for a remapped depth range it could be something like 0.5-0.6, then the custom projection will render stuff using its entire near-far range and remap it to the 0.5-0.6 depth buffer range.
in the shader code, i force perspective divide to be done in the vert shader and put the result as clip space pos(where w = 1, with 1 being the clip range instead of the usual view depth), also for the z component i put in linear depth.
so the clippos set up is something like
(posvs.x/posvs.w,posvs.y/posvs.w, linear Z, 1)
my problem arise when vertex get pass the custom projection’s near(also far as well, but not important here).
here is a simple scene hopefully to make the problem clearer. (by the way, i switch to DX api in editor so that i can launch RenderDoc without crashing)
got 2 set of simple primitives sitting very close to the main cam and the custom projection object(both main cam and custom projection obj has the same camera setting, meaning projection is the same here in this set up)
the left set is rendering with custom projection, the right set is with the main camera.
take note the both triangle has the front most vert poking out of the frustum.
as can be seen, the left set is not clipping at all (at least not properly like the right set. tho the mesh will eventually got clip if all verts are out of the frustum. still lets focus back on the main issue here)
lets just focus on the triangle for the sake of simplicity, here is the clippos data
for the left set triangle(the set that is not clipping properly).
the z component is looking exactly right according to my shader code, since the back 2 verts are still within the frustum, so the z for these 2 verts are the remapped depth values.
the front most vert is also correct as whenever the view depth is less than near(in this case, this vert has physically gone pass the projection’s near), the shader code will put z back to its non-remapped z, so 1.00213.
now for triangle in the right set:
since its being render normally, so no remapped z value, so the data also checks out. take note the front most vert also got the same z value just like the left set.
when looking in render doc with depth test overlay, the left set triangle got pass all the ztest for all pixel, while the front most vert z is clearly out of clip range 1
still, all pixels in this triangle got pass the ztest, as if it never compare z to 1 which should be the default clear value for DX at this point.
then when looking at the right set triangle(where the front most vert has the same z value as with the left set triangle) can do proper depth test correctly
question:
how can the GPU not clipping while my clippos value is clearly out side of clip range?
is there some kind of secret enforcing depth test range setting that i need to enable when using cutom projection? coz from what is shown in RenderDoc, no early z test (for out side clip range, early z will still work when in side frustum) is happening for the left set primitive where they are being render with custom projection and depth remapped.