d3d12: Support R16G16B16A16_FLOAT display targets

Since GDI doesn't support this format, we need a fallback path to
get contents on-screen if we're not using DXGI. For that scenario,
we allocate a proxy display target and blit during frontbuffer flush.

Once we have that fallback in place, we can override the sw winsys
format support check for that format.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/27512>

src/gallium/drivers/d3d12/d3d12_resource.cpp

@@ -86,6 +86,8 @@ d3d12_resource_destroy(struct pipe_screen *pscreen,
       screen->winsys->displaytarget_destroy(screen->winsys, resource->dt);
    }
 
+   if (resource->dt_proxy)
+      pipe_resource_reference(&resource->dt_proxy, NULL);
    threaded_resource_deinit(presource);
    if (can_map_directly(presource))
       util_range_destroy(&resource->valid_buffer_range);
@@ -369,6 +371,7 @@ init_texture(struct d3d12_screen *screen,
 
    if (screen->winsys && (templ->bind & PIPE_BIND_DISPLAY_TARGET)) {
       struct sw_winsys *winsys = screen->winsys;
+      if (winsys->is_displaytarget_format_supported(winsys, res->base.b.bind, res->base.b.format)) {
          res->dt = winsys->displaytarget_create(screen->winsys,
                                                 res->base.b.bind,
                                                 res->base.b.format,
@@ -377,6 +380,15 @@ init_texture(struct d3d12_screen *screen,
                                                 64, NULL,
                                                 &res->dt_stride);
          res->dt_refcount = 1;
+      } else {
+         assert(res->base.b.format == PIPE_FORMAT_R16G16B16A16_FLOAT); /* The only format we proxy right now */
+         struct pipe_resource proxy_templ = *templ;
+         proxy_templ.format = PIPE_FORMAT_R8G8B8A8_UNORM;
+         res->dt_proxy = screen->base.resource_create(&screen->base, &proxy_templ);
+         if (!res->dt_proxy)
+            return false;
+         assert(d3d12_resource(res->dt_proxy)->dt);
+      }
    }
 
    res->bo = d3d12_bo_wrap_res(screen, d3d12_res, init_residency);

src/gallium/drivers/d3d12/d3d12_resource.h

@@ -48,9 +48,12 @@ struct d3d12_resource {
    unsigned int plane_slice;
    struct pipe_resource* first_plane;
    unsigned mip_levels;
+
    struct sw_displaytarget *dt;
    unsigned dt_refcount; /* For planar resources sharing the dt pointer */
    unsigned dt_stride;
+   struct pipe_resource *dt_proxy;
+
    struct util_range valid_buffer_range;
    uint32_t bind_counts[PIPE_SHADER_TYPES][D3D12_RESOURCE_BINDING_TYPES];
    unsigned generation_id;

src/gallium/drivers/d3d12/d3d12_screen.cpp

@@ -634,7 +634,8 @@ d3d12_is_format_supported(struct pipe_screen *pscreen,
    }
 
    if (bind & PIPE_BIND_DISPLAY_TARGET) {
-      if (!screen->winsys->is_displaytarget_format_supported(screen->winsys, bind, format))
+      enum pipe_format dt_format = format == PIPE_FORMAT_R16G16B16A16_FLOAT ? PIPE_FORMAT_R8G8B8A8_UNORM : format;
+      if (!screen->winsys->is_displaytarget_format_supported(screen->winsys, bind, dt_format))
          return false;
    }
 
@@ -798,6 +799,29 @@ d3d12_flush_frontbuffer(struct pipe_screen * pscreen,
    if (!winsys || !pctx)
      return;
 
+   assert(res->dt || res->dt_proxy);
+   if (res->dt_proxy) {
+     struct pipe_blit_info blit;
+
+     memset(&blit, 0, sizeof(blit));
+     blit.dst.resource = res->dt_proxy;
+     blit.dst.box.width = blit.dst.resource->width0;
+     blit.dst.box.height = blit.dst.resource->height0;
+     blit.dst.box.depth = 1;
+     blit.dst.format = blit.dst.resource->format;
+     blit.src.resource = pres;
+     blit.src.box.width = blit.src.resource->width0;
+     blit.src.box.height = blit.src.resource->height0;
+     blit.src.box.depth = 1;
+     blit.src.format = blit.src.resource->format;
+     blit.mask = PIPE_MASK_RGBA;
+     blit.filter = PIPE_TEX_FILTER_NEAREST;
+
+     pctx->blit(pctx, &blit);
+     pres = res->dt_proxy;
+     res = d3d12_resource(pres);
+   }
+
    assert(res->dt);
    void *map = winsys->displaytarget_map(winsys, res->dt, 0);