Revert change to default depth clear value in draw_list_begin()

[clayjohn]

Fixes: #90627

The reverse Z PR change the default clear depth specified by draw_list_begin(). This was convenient as many uses of draw_list_begin() should be clearing to 0.0 now. However, this broke the lightmapper which uses the RD API outside of the renderer and does not use reverse Z. It will also break any user project which uses the RD API directly and relies on the default clear value.

Ultimately, its better to revert back to the previous default value as this change was technically a breaking change.

[akien-mga]

Thanks!

[darksylinc]

How is it that an external component can use the RD API without Reverse Z?

Setting the default value to Normal Z when the engine internal doesn't support Normal Z will cause a lot of headaches in the future.

Alternatively introduce draw_list_begin2 and deprecate draw_list_begin

[clayjohn]

How is it that an external component can use the RD API without Reverse Z?

Setting the default value to Normal Z when the engine internal doesn't support Normal Z will cause a lot of headaches in the future.

Alternatively introduce draw_list_begin2 and deprecate draw_list_begin

When a user uses the RD API they create their own framebuffers, render passes etc. So they can use whatever depth representation they want.

The RD API itself doesn't use reverse z or non reverse z, the way that Vulkan doesn't use reverse z or non reverse z. The decision is totally in user space.

[darksylinc]

But isn't the Reverse Z sent through the projection matrix? Or are they dodging the projection matrix (which is almost always a bad idea).

[clayjohn]

They supply their own projection matrix. The RD API is it's own thing. It's just an abstraction layer. We use it for our renderer internally. But users can use it for whatever they like.