Initial conditional rendering support (#1012)

* Initial conditional rendering support

* Properly reset state

* Support conditional modes and skeleton a counter cache for future host conditional rendering

* Address PR feedback

Ryujinx.Graphics.Gpu/Engine/MethodConditionalRendering.cs

@@ -0,0 +1,82 @@
+using Ryujinx.Common.Logging;
+using Ryujinx.Graphics.Gpu.State;
+
+namespace Ryujinx.Graphics.Gpu.Engine
+{
+    partial class Methods
+    {
+        /// <summary>
+        /// Checks if draws and clears should be performed, according
+        /// to currently set conditional rendering conditions.
+        /// </summary>
+        /// <param name="state">GPU state</param>
+        /// <returns>True if rendering is enabled, false otherwise</returns>
+        private bool GetRenderEnable(GpuState state)
+        {
+            ConditionState condState = state.Get<ConditionState>(MethodOffset.ConditionState);
+
+            switch (condState.Condition)
+            {
+                case Condition.Always:
+                    return true;
+                case Condition.Never:
+                    return false;
+                case Condition.ResultNonZero:
+                    return CounterNonZero(condState.Address.Pack());
+                case Condition.Equal:
+                    return CounterCompare(condState.Address.Pack(), true);
+                case Condition.NotEqual:
+                    return CounterCompare(condState.Address.Pack(), false);
+            }
+
+            Logger.PrintWarning(LogClass.Gpu, $"Invalid conditional render condition \"{condState.Condition}\".");
+
+            return true;
+        }
+
+        /// <summary>
+        /// Checks if the counter value at a given GPU memory address is non-zero.
+        /// </summary>
+        /// <param name="gpuVa">GPU virtual address of the counter value</param>
+        /// <returns>True if the value is not zero, false otherwise</returns>
+        private bool CounterNonZero(ulong gpuVa)
+        {
+            if (!FindAndFlush(gpuVa))
+            {
+                return false;
+            }
+
+            return _context.MemoryAccessor.ReadUInt64(gpuVa) != 0;
+        }
+
+        /// <summary>
+        /// Checks if the counter at a given GPU memory address passes a specified equality comparison.
+        /// </summary>
+        /// <param name="gpuVa">GPU virtual address</param>
+        /// <param name="isEqual">True to check if the values are equal, false to check if they are not equal</param>
+        /// <returns>True if the condition is met, false otherwise</returns>
+        private bool CounterCompare(ulong gpuVa, bool isEqual)
+        {
+            if (!FindAndFlush(gpuVa) && !FindAndFlush(gpuVa + 16))
+            {
+                return false;
+            }
+
+            ulong x = _context.MemoryAccessor.ReadUInt64(gpuVa);
+            ulong y = _context.MemoryAccessor.ReadUInt64(gpuVa + 16);
+
+            return isEqual ? x == y : x != y;
+        }
+
+        /// <summary>
+        /// Tries to find a counter that is supposed to be written at the specified address,
+        /// flushing if necessary.
+        /// </summary>
+        /// <param name="gpuVa">GPU virtual address where the counter is supposed to be written</param>
+        /// <returns>True if a counter value is found at the specified address, false otherwise</returns>
+        private bool FindAndFlush(ulong gpuVa)
+        {
+            return _counterCache.Contains(gpuVa);
+        }
+    }
+}