Add a null graphics system (enable with --gpu=null)

Still uses vulkan to drive xenia UI, may look into decoupling later.

src/xenia/gpu/null/null_command_processor.h

@@ -0,0 +1,48 @@
+/**
+ ******************************************************************************
+ * Xenia : Xbox 360 Emulator Research Project                                 *
+ ******************************************************************************
+ * Copyright 2016 Ben Vanik. All rights reserved.                             *
+ * Released under the BSD license - see LICENSE in the root for more details. *
+ ******************************************************************************
+ */
+
+#ifndef XENIA_GPU_NULL_NULL_COMMAND_PROCESSOR_H_
+#define XENIA_GPU_NULL_NULL_COMMAND_PROCESSOR_H_
+
+#include "xenia/gpu/command_processor.h"
+#include "xenia/gpu/null/null_graphics_system.h"
+#include "xenia/gpu/xenos.h"
+#include "xenia/kernel/kernel_state.h"
+
+namespace xe {
+namespace gpu {
+namespace null {
+
+class NullCommandProcessor : public CommandProcessor {
+ public:
+  NullCommandProcessor(NullGraphicsSystem* graphics_system,
+                       kernel::KernelState* kernel_state);
+  ~NullCommandProcessor();
+
+ private:
+  bool SetupContext() override;
+  void ShutdownContext() override;
+
+  void PerformSwap(uint32_t frontbuffer_ptr, uint32_t frontbuffer_width,
+                   uint32_t frontbuffer_height) override;
+
+  Shader* LoadShader(ShaderType shader_type, uint32_t guest_address,
+                     const uint32_t* host_address,
+                     uint32_t dword_count) override;
+
+  bool IssueDraw(PrimitiveType prim_type, uint32_t index_count,
+                 IndexBufferInfo* index_buffer_info) override;
+  bool IssueCopy() override;
+};
+
+}  // namespace null
+}  // namespace gpu
+}  // namespace xe
+
+#endif  // XENIA_GPU_NULL_NULL_COMMAND_PROCESSOR_H_