[idd] postprocess: centralize color transform state

idd/LGIdd/postprocess/D12FrameFormat.cpp

@@ -22,6 +22,55 @@
 
 #include <cstring>
 
+namespace
+{
+  bool NearlyEqual(float a, float b, float tolerance)
+  {
+    const float delta = a - b;
+    return delta >= -tolerance && delta <= tolerance;
+  }
+
+  bool Identity(const D12ColorTransform& transform)
+  {
+    static const float matrixTolerance = 1.0f / 1048576.0f;
+    static const float lutTolerance    = 1.0f / 65535.0f;
+
+    if (transform.matrixEnabled)
+    {
+      for (unsigned row = 0; row < 3; ++row)
+        for (unsigned column = 0; column < 4; ++column)
+        {
+          const float expected  = row == column ? 1.0f : 0.0f;
+          const float effective =
+            transform.matrix[row][column] * transform.scalar;
+          if (!NearlyEqual(effective, expected, matrixTolerance))
+            return false;
+        }
+    }
+
+    if (transform.lutEnabled)
+      for (unsigned i = 0; i < 4096; ++i)
+      {
+        const float expected = static_cast<float>(i) / 4095.0f;
+        if (!NearlyEqual(transform.lut[i][0], expected, lutTolerance) ||
+            !NearlyEqual(transform.lut[i][1], expected, lutTolerance) ||
+            !NearlyEqual(transform.lut[i][2], expected, lutTolerance))
+          return false;
+      }
+
+    return true;
+  }
+}
+
+std::shared_ptr<const D12ColorTransform> D12::Transform(
+  const std::shared_ptr<const D12ColorTransform>& transform)
+{
+  if (!transform || (!transform->matrixEnabled && !transform->lutEnabled) ||
+      Identity(*transform))
+    return nullptr;
+  return transform;
+}
+
 FrameType D12::Type(DXGI_FORMAT format)
 {
   switch (format)