Map/Unmap constant buffers instead of using UpdateSubResource

(XB1) Drops GPU Busy % on spiral from 65% to 20%

(PC) Drops bgfx::d3d11::RendererContextD3D11::commitShaderConstants
CPU usage by 95% (11.21%->0.66%)

(PC) Overall decreases bgfx::d3d11::RenderContextD3D11::submit CPU
usage by another 34% (27.18%->17.90%)

src/renderer_d3d11.cpp

@@ -8,6 +8,10 @@
 #if BGFX_CONFIG_RENDERER_DIRECT3D11
 #	include "renderer_d3d11.h"
 
+#	if !defined(BGFX_D3D11_MAP_CONSTANT_BUFFERS)
+#		define BGFX_D3D11_MAP_CONSTANT_BUFFERS 0
+#	endif
+
 namespace bgfx { namespace d3d11
 {
 	static wchar_t s_viewNameW[BGFX_CONFIG_MAX_VIEWS][BGFX_CONFIG_MAX_VIEW_NAME];
@@ -462,8 +466,13 @@ namespace bgfx { namespace d3d11
 			, m_flags(BGFX_RESET_NONE)
 			, m_maxAnisotropy(1)
 			, m_currentProgram(NULL)
+#if BGFX_D3D11_MAP_CONSTANT_BUFFERS
+			, m_vsScratch(NULL)
+			, m_fsScratch(NULL)
+#else
 			, m_vsChanges(0)
 			, m_fsChanges(0)
+#endif // BGFX_D3D11_MAP_CONSTANT_BUFFERS
 			, m_rtMsaa(false)
 			, m_ovrRtv(NULL)
 			, m_ovrDsv(NULL)
@@ -1440,6 +1449,8 @@ BX_PRAGMA_DIAGNOSTIC_POP();
 			float proj[16];
 			bx::mtxOrtho(proj, 0.0f, (float)width, (float)height, 0.0f, 0.0f, 1000.0f);
 
+			prepareShaderConstants();
+
 			PredefinedUniform& predefined = program.m_predefined[0];
 			uint8_t flags = predefined.m_type;
 			setShaderUniform(flags, predefined.m_loc, proj, 4);
@@ -1736,12 +1747,16 @@ BX_PRAGMA_DIAGNOSTIC_POP();
 			if (_flags&BGFX_UNIFORM_FRAGMENTBIT)
 			{
 				memcpy(&m_fsScratch[_regIndex], _val, _numRegs*16);
+#if !BGFX_D3D11_MAP_CONSTANT_BUFFERS
 				m_fsChanges += _numRegs;
+#endif
 			}
 			else
 			{
 				memcpy(&m_vsScratch[_regIndex], _val, _numRegs*16);
+#if !BGFX_D3D11_MAP_CONSTANT_BUFFERS
 				m_vsChanges += _numRegs;
+#endif
 			}
 		}
 
@@ -1755,8 +1770,37 @@ BX_PRAGMA_DIAGNOSTIC_POP();
 			setShaderUniform(_flags, _regIndex, _val, _numRegs);
 		}
 
+		void prepareShaderConstants()
+		{
+#if BGFX_D3D11_MAP_CONSTANT_BUFFERS
+			if (NULL != m_currentProgram->m_vsh->m_buffer)
+			{
+				D3D11_MAPPED_SUBRESOURCE mapped;
+				DX_CHECK(m_deviceCtx->Map(m_currentProgram->m_vsh->m_buffer, 0, D3D11_MAP_WRITE_DISCARD, 0, &mapped));
+				m_vsScratch = (uint8_t*)mapped.pData;
+			}
+			if (NULL != m_currentProgram->m_fsh->m_buffer)
+			{
+				D3D11_MAPPED_SUBRESOURCE mapped;
+				DX_CHECK(m_deviceCtx->Map(m_currentProgram->m_fsh->m_buffer, 0, D3D11_MAP_WRITE_DISCARD, 0, &mapped));
+				m_fsScratch = (uint8_t*)mapped.pData;
+			}
+#endif // BGFX_D3D11_MAP_CONSTANT_BUFFERS
+		}
+
 		void commitShaderConstants()
 		{
+#if BGFX_D3D11_MAP_CONSTANT_BUFFERS
+			if (NULL != m_vsScratch)
+			{
+				m_deviceCtx->Unmap(m_currentProgram->m_vsh->m_buffer, 0);
+			}
+			if (NULL != m_fsScratch)
+			{
+				m_deviceCtx->Unmap(m_currentProgram->m_fsh->m_buffer, 0);
+			}
+			m_vsScratch = m_fsScratch = 0;
+#else
 			if (0 < m_vsChanges)
 			{
 				if (NULL != m_currentProgram->m_vsh->m_buffer)
@@ -1776,6 +1820,7 @@ BX_PRAGMA_DIAGNOSTIC_POP();
 
 				m_fsChanges = 0;
 			}
+#endif // BGFX_D3D11_MAP_CONSTANT_BUFFERS
 		}
 
 		void setFrameBuffer(FrameBufferHandle _fbh, bool _msaa = true)
@@ -2518,6 +2563,12 @@ BX_PRAGMA_DIAGNOSTIC_POP();
 					deviceCtx->PSSetShader(fsh->m_pixelShader, NULL, 0);
 					deviceCtx->PSSetConstantBuffers(0, 1, &fsh->m_buffer);
 
+#if BGFX_D3D11_MAP_CONSTANT_BUFFERS
+					D3D11_MAPPED_SUBRESOURCE mapped;
+					DX_CHECK(deviceCtx->Map(fsh->m_buffer, 0, D3D11_MAP_WRITE_DISCARD, 0, &mapped));
+					void* fsScratch = mapped.pData;
+#endif // BGFX_D3D11_MAP_CONSTANT_BUFFERS
+
 					if (BGFX_CLEAR_COLOR_USE_PALETTE & _clear.m_flags)
 					{
 						float mrtClear[BGFX_CONFIG_MAX_FRAME_BUFFER_ATTACHMENTS][4];
@@ -2527,7 +2578,11 @@ BX_PRAGMA_DIAGNOSTIC_POP();
 							memcpy(mrtClear[ii], _palette[index], 16);
 						}
 
+#if BGFX_D3D11_MAP_CONSTANT_BUFFERS
+						memcpy(fsScratch, mrtClear, sizeof(mrtClear));
+#else
 						deviceCtx->UpdateSubresource(fsh->m_buffer, 0, 0, mrtClear, 0, 0);
+#endif // BGFX_D3D11_MAP_CONSTANT_BUFFERS
 					}
 					else
 					{
@@ -2538,8 +2593,20 @@ BX_PRAGMA_DIAGNOSTIC_POP();
 							_clear.m_index[2]*1.0f/255.0f,
 							_clear.m_index[3]*1.0f/255.0f,
 						};
+
+#if BGFX_D3D11_MAP_CONSTANT_BUFFERS
+						memcpy(fsScratch, rgba, sizeof(rgba));
+#else
 						deviceCtx->UpdateSubresource(fsh->m_buffer, 0, 0, rgba, 0, 0);
+#endif // BGFX_D3D11_MAP_CONSTANT_BUFFERS
 					}
+
+#if BGFX_D3D11_MAP_CONSTANT_BUFFERS
+					if (NULL != fsScratch)
+					{
+						deviceCtx->Unmap(fsh->m_buffer, 0);
+					}
+#endif // BGFX_D3D11_MAP_CONSTANT_BUFFERS
 				}
 				else
 				{
@@ -2660,11 +2727,15 @@ BX_PRAGMA_DIAGNOSTIC_POP();
 
 		ProgramD3D11* m_currentProgram;
 
+#if BGFX_D3D11_MAP_CONSTANT_BUFFERS
+		uint8_t* m_vsScratch;
+		uint8_t* m_fsScratch;
+#else
 		uint8_t m_vsScratch[64<<10];
 		uint8_t m_fsScratch[64<<10];
-
 		uint32_t m_vsChanges;
 		uint32_t m_fsChanges;
+#endif // BGFX_D3D11_MAP_CONSTANT_BUFFERS
 
 		FrameBufferHandle m_fbh;
 		bool m_rtMsaa;
@@ -3057,9 +3128,14 @@ BX_PRAGMA_DIAGNOSTIC_POP();
 		{
 			D3D11_BUFFER_DESC desc;
 			desc.ByteWidth = (size + 0xf) & ~0xf;
+#if BGFX_D3D11_MAP_CONSTANT_BUFFERS
+			desc.Usage = D3D11_USAGE_DYNAMIC;
+			desc.CPUAccessFlags = D3D11_CPU_ACCESS_WRITE;
+#else
 			desc.Usage = D3D11_USAGE_DEFAULT;
-			desc.BindFlags = D3D11_BIND_CONSTANT_BUFFER;
 			desc.CPUAccessFlags = 0;
+#endif // BGFX_D3D11_MAP_CONSTANT_BUFFERS
+			desc.BindFlags = D3D11_BIND_CONSTANT_BUFFER;
 			desc.MiscFlags = 0;
 			desc.StructureByteStride = 0;
 			DX_CHECK(s_renderD3D11->m_device->CreateBuffer(&desc, NULL, &m_buffer) );
@@ -4108,6 +4184,12 @@ BX_PRAGMA_DIAGNOSTIC_POP();
 				{
 					ProgramD3D11& program = m_program[programIdx];
 
+#if BGFX_D3D11_MAP_CONSTANT_BUFFERS
+					if (constantsChanged || 0 != program.m_numPredefined)
+					{
+						prepareShaderConstants();
+					}
+#endif // BGFX_D3D11_MAP_CONSTANT_BUFFERS
 					if (constantsChanged)
 					{
 						ConstantBuffer* vcb = program.m_vsh->m_constantBuffer;