render/d3d11: adjust allowed frame 'latency' (frames-in-queue) based on number of active windows, to not unnecessarily block if we have two windows to build frames for; demon/linux: sketch out register writing path, ensure reg read/write paths have slots for other architectures

src/render/d3d11/render_d3d11.c

@@ -548,6 +548,8 @@ r_window_equip(OS_Handle handle)
     r_d3d11_state->device->lpVtbl->CreateRenderTargetView(r_d3d11_state->device, (ID3D11Resource *)window->framebuffer, &framebuffer_rtv_desc, &window->framebuffer_rtv);
     
     result = r_d3d11_handle_from_window(window);
+    r_d3d11_state->window_count += 1;
+    r_d3d11_state->dxgi_device->lpVtbl->SetMaximumFrameLatency(r_d3d11_state->dxgi_device, Clamp(1, r_d3d11_state->window_count, 16));
   }
   ProfEnd();
   return result;
@@ -571,6 +573,8 @@ r_window_unequip(OS_Handle handle, R_Handle equip_handle)
     window->swapchain->lpVtbl->Release(window->swapchain);
     window->generation += 1;
     SLLStackPush(r_d3d11_state->first_free_window, window);
+    r_d3d11_state->window_count -= 1;
+    r_d3d11_state->dxgi_device->lpVtbl->SetMaximumFrameLatency(r_d3d11_state->dxgi_device, Clamp(1, r_d3d11_state->window_count, 16));
   }
   ProfEnd();
 }

src/render/d3d11/render_d3d11.h

@@ -129,6 +129,7 @@ struct R_D3D11_State
 {
   // rjf: state
   Arena *arena;
+  U64 window_count;
   R_D3D11_Window *first_free_window;
   R_D3D11_Tex2D *first_free_tex2d;
   R_D3D11_Buffer *first_free_buffer;