texture_cache: Implement rendering to 3D textures

This allows rendering to 3D textures with more than one slice.
Applications are allowed to render to more than one slice of a texture
using gl_Layer from a VTG shader.

This also requires reworking how 3D texture collisions are handled, for
now, this commit allows rendering to slices but not to miplevels. When a
render target attempts to write to a mipmap, we fallback to the previous
implementation (copying or flushing as needed).

- Fixes color correction 3D textures on UE4 games (rainbow effects).
- Allows Xenoblade games to render to 3D textures directly.

1 files changed, 3 insertions, 4 deletions

diff --git a/src/video_core/texture_cache/surface_base.cpp b/src/video_core/texture_cache/surface_base.cpp
index 715f39d0d..94d3a6ae5 100644
--- a/src/video_core/texture_cache/surface_base.cpp
+++ b/src/video_core/texture_cache/surface_base.cpp
@@ -248,12 +248,11 @@ void SurfaceBaseImpl::FlushBuffer(Tegra::MemoryManager& memory_manager,
 
     // Use an extra temporal buffer
     auto& tmp_buffer = staging_cache.GetBuffer(1);
-    // Special case for 3D Texture Segments
-    const bool must_read_current_data =
-        params.block_depth > 0 && params.target == VideoCore::Surface::SurfaceTarget::Texture2D;
     tmp_buffer.resize(guest_memory_size);
     host_ptr = tmp_buffer.data();
-    if (must_read_current_data) {
+
+    if (params.target == SurfaceTarget::Texture3D) {
+        // Special case for 3D texture segments
         memory_manager.ReadBlockUnsafe(gpu_addr, host_ptr, guest_memory_size);
     }