RenderState: Approximate logic op with blending if unsupported

This is a giant hack which was previously removed because it causes
broken rendering. However, it seems that some devices still do not
support logical operations (looking at you, Adreno/Mali). Therefore, for
a handful of cases where the hack actually makes things slightly better,
we can use it.

... but not without spamming the log with warnings. With my warning
message PR, we can inform the users before emulation starts anyway.

1 files changed, 36 insertions, 0 deletions

diff --git a/Source/Core/VideoCommon/RenderState.cpp b/Source/Core/VideoCommon/RenderState.cpp
index 04d8804f0c..6d6f892979 100644
--- a/Source/Core/VideoCommon/RenderState.cpp
+++ b/Source/Core/VideoCommon/RenderState.cpp
@@ -167,6 +167,42 @@ void BlendingState::Generate(const BPMemory& bp)
   }
 }
 
+void BlendingState::ApproximateLogicOpWithBlending()
+{
+  // Any of these which use SRC as srcFactor or DST as dstFactor won't be correct.
+  // This is because the two are aliased to one another (see the enum).
+  struct LogicOpApproximation
+  {
+    bool subtract;
+    BlendMode::BlendFactor srcfactor;
+    BlendMode::BlendFactor dstfactor;
+  };
+  static constexpr std::array<LogicOpApproximation, 16> approximations = {{
+      {false, BlendMode::ZERO, BlendMode::ZERO},            // CLEAR
+      {false, BlendMode::DSTCLR, BlendMode::ZERO},          // AND
+      {true, BlendMode::ONE, BlendMode::INVSRCCLR},         // AND_REVERSE
+      {false, BlendMode::ONE, BlendMode::ZERO},             // COPY
+      {true, BlendMode::DSTCLR, BlendMode::ONE},            // AND_INVERTED
+      {false, BlendMode::ZERO, BlendMode::ONE},             // NOOP
+      {false, BlendMode::INVDSTCLR, BlendMode::INVSRCCLR},  // XOR
+      {false, BlendMode::INVDSTCLR, BlendMode::ONE},        // OR
+      {false, BlendMode::INVSRCCLR, BlendMode::INVDSTCLR},  // NOR
+      {false, BlendMode::INVSRCCLR, BlendMode::ZERO},       // EQUIV
+      {false, BlendMode::INVDSTCLR, BlendMode::INVDSTCLR},  // INVERT
+      {false, BlendMode::ONE, BlendMode::INVDSTALPHA},      // OR_REVERSE
+      {false, BlendMode::INVSRCCLR, BlendMode::INVSRCCLR},  // COPY_INVERTED
+      {false, BlendMode::INVSRCCLR, BlendMode::ONE},        // OR_INVERTED
+      {false, BlendMode::INVDSTCLR, BlendMode::INVSRCCLR},  // NAND
+      {false, BlendMode::ONE, BlendMode::ONE},              // SET
+  }};
+
+  logicopenable = false;
+  blendenable = true;
+  subtract = approximations[logicmode].subtract;
+  srcfactor = approximations[logicmode].srcfactor;
+  dstfactor = approximations[logicmode].dstfactor;
+}
+
 BlendingState& BlendingState::operator=(const BlendingState& rhs)
 {
   hex = rhs.hex;