Rework dummy image handling to avoid RTX HDR driver bug

As a side effect, it avoids useless allocations and uploads of
a zeroed memory buffer to clear the dummy image textures.

src/platform/windows/display_vram.cpp

@@ -125,6 +125,9 @@ namespace platf::dxgi {
     // the first successful capture of a desktop frame
     bool dummy = false;
 
+    // Set to true if the image is blank (contains no content at all, including a cursor)
+    bool blank = true;
+
     // Unique identifier for this image
     uint32_t id = 0;
 
@@ -382,6 +385,7 @@ namespace platf::dxgi {
       }
 
       auto &img = (img_d3d_t &) img_base;
+      if (!img.blank) {
         auto &img_ctx = img_ctx_map[img.id];
 
         // Open the shared capture texture with our ID3D11Device
@@ -414,6 +418,7 @@ namespace platf::dxgi {
 
         ID3D11ShaderResourceView *emptyShaderResourceView = nullptr;
         device_ctx->PSSetShaderResources(0, 1, &emptyShaderResourceView);
+      }
 
       return 0;
     }
@@ -1144,6 +1149,9 @@ namespace platf::dxgi {
         return { nullptr, nullptr };
       }
 
+      // Clear the blank flag now that we're ready to capture into the image
+      d3d_img->blank = false;
+
       return { std::move(d3d_img), std::move(lock_helper) };
     };
 
@@ -1289,15 +1297,14 @@ namespace platf::dxgi {
         // Clear the image if it has been used as a dummy.
         // It can have the mouse cursor blended onto it.
         auto old_d3d_img = (img_d3d_t *) img_out.get();
-        bool reclear_dummy = old_d3d_img->dummy && old_d3d_img->capture_texture;
+        bool reclear_dummy = !old_d3d_img->blank && old_d3d_img->capture_texture;
 
         auto [d3d_img, lock] = get_locked_d3d_img(img_out, true);
         if (!d3d_img) return capture_e::error;
 
         if (reclear_dummy) {
-          auto dummy_data = std::make_unique<std::uint8_t[]>(d3d_img->row_pitch * d3d_img->height);
+          const float rgb_black[] = { 0.0f, 0.0f, 0.0f, 0.0f };
-          std::fill_n(dummy_data.get(), d3d_img->row_pitch * d3d_img->height, 0);
+          device_ctx->ClearRenderTargetView(d3d_img->capture_rt.get(), rgb_black);
-          device_ctx->UpdateSubresource(d3d_img->capture_texture.get(), 0, nullptr, dummy_data.get(), d3d_img->row_pitch, 0);
         }
 
         if (blend_mouse_cursor_flag) {
@@ -1409,6 +1416,7 @@ namespace platf::dxgi {
     img->width = width_before_rotation;
     img->height = height_before_rotation;
     img->id = next_image_id++;
+    img->blank = true;
 
     return img;
   }
@@ -1456,20 +1464,7 @@ namespace platf::dxgi {
     t.BindFlags = D3D11_BIND_SHADER_RESOURCE | D3D11_BIND_RENDER_TARGET;
     t.MiscFlags = D3D11_RESOURCE_MISC_SHARED_NTHANDLE | D3D11_RESOURCE_MISC_SHARED_KEYEDMUTEX;
 
-    HRESULT status;
+    auto status = device->CreateTexture2D(&t, nullptr, &img->capture_texture);
-    if (dummy) {
-      auto dummy_data = std::make_unique<std::uint8_t[]>(img->row_pitch * img->height);
-      std::fill_n(dummy_data.get(), img->row_pitch * img->height, 0);
-      D3D11_SUBRESOURCE_DATA initial_data {
-        dummy_data.get(),
-        (UINT) img->row_pitch,
-        0
-      };
-      status = device->CreateTexture2D(&t, &initial_data, &img->capture_texture);
-    }
-    else {
-      status = device->CreateTexture2D(&t, nullptr, &img->capture_texture);
-    }
     if (FAILED(status)) {
       BOOST_LOG(error) << "Failed to create img buf texture [0x"sv << util::hex(status).to_string_view() << ']';
       return -1;