rhi: Add a flag to suppress D3D11 smoke test warnings

Applicable to D3D11 only, although the flag is general enough that
other backends could use it if it made sense for them.

This allows Qt Quick to state that warnings about QRhi::create()
failures that lead to retrying with a different set of flags
(PreferSoftwareRenderer to get to use the WARP software rasterizer)
should be suppressed and turned to regular categorized debug prints.

Other users, e.g. an application directly working with QRhi may not
want this. A create() failure must be complemented by an unconditional
qWarning since normally that is pretty serious error. Hence the opt-in
flag.

Task-number: QTBUG-117926
Change-Id: I808bd1670b631e2068b566ab08589e1783f62ca5
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>

3 files changed, 35 insertions, 12 deletions

diff --git a/src/gui/rhi/qrhi.cpp b/src/gui/rhi/qrhi.cpp
index 0728d7824d..67b8d2d134 100644
--- a/src/gui/rhi/qrhi.cpp
+++ b/src/gui/rhi/qrhi.cpp
@@ -665,6 +665,17 @@ Q_LOGGING_CATEGORY(QRHI_LOG_INFO, "qt.rhi.general")
     mechanisms for shader/program binaries provided by Qt. Writing to those may
     get disabled whenever this flag is set since storing program binaries to
     multiple caches is not sensible.
+
+    \value SuppressSmokeTestWarnings Indicates that, with backends where this
+    is relevant, certain, non-fatal QRhi::create() failures should not
+    produce qWarning() calls. For example, with D3D11, passing this flag
+    makes a number of warning messages (that appear due to QRhi::create()
+    failing) to become categorized debug prints instead under the commonly used
+    \c{qt.rhi.general} logging category. This can be used by engines, such as
+    Qt Quick, that feature fallback logic, i.e. they retry calling create()
+    with a different set of flags (such as, \l PreferSoftwareRenderer), in order
+    to hide the unconditional warnings from the output that would be printed
+    when the first create() attempt had failed.
  */
 
 /*!
diff --git a/src/gui/rhi/qrhi.h b/src/gui/rhi/qrhi.h
index 770233bb51..f1620c11fa 100644
--- a/src/gui/rhi/qrhi.h
+++ b/src/gui/rhi/qrhi.h
@@ -1787,7 +1787,8 @@ public:
         EnableDebugMarkers = 1 << 0,
         PreferSoftwareRenderer = 1 << 1,
         EnablePipelineCacheDataSave = 1 << 2,
-        EnableTimestamps = 1 << 3
+        EnableTimestamps = 1 << 3,
+        SuppressSmokeTestWarnings = 1 << 4
     };
     Q_DECLARE_FLAGS(Flags, Flag)
 
diff --git a/src/gui/rhi/qrhid3d11.cpp b/src/gui/rhi/qrhid3d11.cpp
index 4dcda25d18..d357a6b2db 100644
--- a/src/gui/rhi/qrhid3d11.cpp
+++ b/src/gui/rhi/qrhid3d11.cpp
@@ -291,21 +291,24 @@ bool QRhiD3D11::create(QRhi::Flags flags)
             return false;
         }
 
+        const bool supports11_1 = SUCCEEDED(ctx->QueryInterface(__uuidof(ID3D11DeviceContext1), reinterpret_cast<void **>(&context)));
+        ctx->Release();
+        if (!supports11_1) {
+            qWarning("ID3D11DeviceContext1 not supported");
+            return false;
+        }
+
         // Test if creating a Shader Model 5.0 vertex shader works; we want to
         // fail already in create() if that's not the case.
         ID3D11VertexShader *testShader = nullptr;
         if (SUCCEEDED(dev->CreateVertexShader(g_testVertexShader, sizeof(g_testVertexShader), nullptr, &testShader))) {
             testShader->Release();
         } else {
-            qWarning("D3D11 smoke test failed (failed to create vertex shader)");
-            ctx->Release();
-            return false;
-        }
-
-        const bool supports11_1 = SUCCEEDED(ctx->QueryInterface(__uuidof(ID3D11DeviceContext1), reinterpret_cast<void **>(&context)));
-        ctx->Release();
-        if (!supports11_1) {
-            qWarning("ID3D11DeviceContext1 not supported");
+            static const char *msg = "D3D11 smoke test: Failed to create vertex shader";
+            if (flags.testFlag(QRhi::SuppressSmokeTestWarnings))
+                qCDebug(QRHI_LOG_INFO, "%s", msg);
+            else
+                qWarning("%s", msg);
             return false;
         }
 
@@ -315,11 +318,19 @@ bool QRhiD3D11::create(QRhi::Flags flags)
             // still not support this D3D_FEATURE_LEVEL_11_1 feature. (e.g.
             // because it only does 11_0)
             if (!features.ConstantBufferOffsetting) {
-                qWarning("Constant buffer offsetting is not supported by the driver");
+                static const char *msg = "D3D11 smoke test: Constant buffer offsetting is not supported by the driver";
+                if (flags.testFlag(QRhi::SuppressSmokeTestWarnings))
+                    qCDebug(QRHI_LOG_INFO, "%s", msg);
+                else
+                    qWarning("%s", msg);
                 return false;
             }
         } else {
-            qWarning("Failed to query D3D11_FEATURE_D3D11_OPTIONS");
+            static const char *msg = "D3D11 smoke test: Failed to query D3D11_FEATURE_D3D11_OPTIONS";
+            if (flags.testFlag(QRhi::SuppressSmokeTestWarnings))
+                qCDebug(QRHI_LOG_INFO, "%s", msg);
+            else
+                qWarning("%s", msg);
             return false;
         }
     } else {