Merge pull request #327 from ouchihao/codex/fix-295-retained-dpi

fix(ui): refresh DPI when reusing render targets

ui/src/DeviceResources.cpp

@@ -78,6 +78,8 @@ bool DeviceResources::EnsureForWindow(HWND hwnd)
     }
     if (hwndRenderTarget_)
     {
+        const FLOAT dpi = DpiForHwnd();
+        hwndRenderTarget_->SetDpi(dpi, dpi);
         return true;
     }
 
@@ -143,6 +145,8 @@ bool DeviceResources::EnsureForComposition(HWND hwnd)
 
     if (composition_ && deviceContext_ && swapChain_ && pixelWidth_ >= width && pixelHeight_ >= height)
     {
+        const FLOAT dpi = DpiForHwnd();
+        deviceContext_->SetDpi(dpi, dpi);
         return true;
     }
 

ui/tests/CMakeLists.txt

@@ -2,6 +2,7 @@ set(TEST_EXECUTABLE_NAME "msimeui-tests")
 
 add_executable(${TEST_EXECUTABLE_NAME}
     src/main.cpp
+    src/test_device_resources.cpp
     src/test_fonts.cpp
     src/test_layout.cpp
     src/test_font_fallback.cpp

ui/tests/src/test_device_resources.cpp

@@ -0,0 +1,83 @@
+#include "tests/includes/test_framework.h"
+
+#include "msimeui/DeviceResources.h"
+
+#include <cmath>
+#include <cstdio>
+
+namespace
+{
+class HiddenWindow
+{
+  public:
+    HiddenWindow()
+    {
+        REQUIRE(SUCCEEDED(CoInitializeEx(nullptr, COINIT_APARTMENTTHREADED)));
+        hwnd = CreateWindowExW(WS_EX_NOREDIRECTIONBITMAP, L"STATIC", L"DPI resource test", WS_POPUP, 0, 0, 256, 128,
+                               nullptr, nullptr, GetModuleHandleW(nullptr), nullptr);
+        REQUIRE(hwnd != nullptr);
+    }
+
+    ~HiddenWindow()
+    {
+        DestroyWindow(hwnd);
+        CoUninitialize();
+    }
+
+    HWND hwnd = nullptr;
+};
+
+void CheckReusedTargetDpi(bool composition)
+{
+    HiddenWindow window;
+    msimeui::DeviceResources resources;
+    const auto ensure = [&]() {
+        return composition ? resources.EnsureForComposition(window.hwnd) : resources.EnsureForWindow(window.hwnd);
+    };
+    REQUIRE(ensure());
+    ID2D1RenderTarget *const target = resources.GetRenderTarget();
+    REQUIRE(target != nullptr);
+    const float windowDpi = static_cast<float>(GetDpiForWindow(window.hwnd));
+
+    // Reproduce the retained render target from the previous monitor DPI without
+    // changing the user's display settings. Reuse must refresh DPI, not recreate it.
+    for (const float previousDpi : {windowDpi / 2.0f, 96.0f, 120.0f, 144.0f, 192.0f, windowDpi * 2.0f})
+    {
+        target->SetDpi(previousDpi, previousDpi);
+        REQUIRE(ensure());
+        REQUIRE(resources.GetRenderTarget() == target);
+        float dpiX = 0.0f;
+        float dpiY = 0.0f;
+        target->GetDpi(&dpiX, &dpiY);
+        std::printf("%s retained DPI %.0f -> window %.0f, target %.0f/%.0f\n", composition ? "composition" : "HWND",
+                    previousDpi, windowDpi, dpiX, dpiY);
+        REQUIRE_NEAR(dpiX, windowDpi);
+        REQUIRE_NEAR(dpiY, windowDpi);
+        const D2D1_SIZE_F size = target->GetSize();
+        const D2D1_SIZE_U pixels = target->GetPixelSize();
+        REQUIRE_NEAR(size.width, pixels.width * 96.0f / windowDpi);
+        REQUIRE_NEAR(size.height, pixels.height * 96.0f / windowDpi);
+    }
+
+    // A smaller client area also reuses the larger composition surface.
+    REQUIRE(SetWindowPos(window.hwnd, nullptr, 0, 0, 128, 64, SWP_NOMOVE | SWP_NOZORDER | SWP_NOACTIVATE));
+    target->SetDpi(windowDpi * 1.25f, windowDpi * 1.25f);
+    REQUIRE(ensure());
+    REQUIRE(resources.GetRenderTarget() == target);
+    float dpiX = 0.0f;
+    float dpiY = 0.0f;
+    target->GetDpi(&dpiX, &dpiY);
+    REQUIRE_NEAR(dpiX, windowDpi);
+    REQUIRE_NEAR(dpiY, windowDpi);
+}
+} // namespace
+
+TEST_CASE(hwnd_target_refreshes_dpi_when_reused)
+{
+    CheckReusedTargetDpi(false);
+}
+
+TEST_CASE(composition_target_refreshes_dpi_when_reused)
+{
+    CheckReusedTargetDpi(true);
+}