premultiplied backbuffer for UWP/SwapchainPanel (#2837)

* premultiplied backbuffer for UWP/SwapchainPanel

* init flag

* caps and feedback/opengl premul

* reduced #ifdef form

* removed ifdef

bindings/bf/bgfx.bf

@@ -997,6 +997,11 @@ public static class bgfx
 		/// Suspend rendering.
 		/// </summary>
 		Suspend                = 0x00080000,
+	
+		/// <summary>
+		/// Transparent backbuffer. Availability depends on: `BGFX_CAPS_TRANSPARENT_BACKBUFFER`.
+		/// </summary>
+		TransparentBackbuffer  = 0x00100000,
 		FullscreenShift        = 0,
 		FullscreenMask         = 0x00000001,
 		ReservedShift          = 31,
@@ -1100,52 +1105,57 @@ public static class bgfx
 		/// Texture blit is supported.
 		/// </summary>
 		TextureBlit            = 0x0000000000040000,
-		TextureCompareReserved = 0x0000000000080000,
+	
+		/// <summary>
+		/// Transparent back buffer supported.
+		/// </summary>
+		TransparentBackbuffer  = 0x0000000000080000,
+		TextureCompareReserved = 0x0000000000100000,
 	
 		/// <summary>
 		/// Texture compare less equal mode is supported.
 		/// </summary>
-		TextureCompareLequal   = 0x0000000000100000,
+		TextureCompareLequal   = 0x0000000000200000,
 	
 		/// <summary>
 		/// Cubemap texture array is supported.
 		/// </summary>
-		TextureCubeArray       = 0x0000000000200000,
+		TextureCubeArray       = 0x0000000000400000,
 	
 		/// <summary>
 		/// CPU direct access to GPU texture memory.
 		/// </summary>
-		TextureDirectAccess    = 0x0000000000400000,
+		TextureDirectAccess    = 0x0000000000800000,
 	
 		/// <summary>
 		/// Read-back texture is supported.
 		/// </summary>
-		TextureReadBack        = 0x0000000000800000,
+		TextureReadBack        = 0x0000000001000000,
 	
 		/// <summary>
 		/// Vertex attribute half-float is supported.
 		/// </summary>
-		VertexAttribHalf       = 0x0000000001000000,
+		VertexAttribHalf       = 0x0000000002000000,
 	
 		/// <summary>
 		/// Vertex attribute 10_10_10_2 is supported.
 		/// </summary>
-		VertexAttribUint10     = 0x0000000002000000,
+		VertexAttribUint10     = 0x0000000004000000,
 	
 		/// <summary>
 		/// Rendering with VertexID only is supported.
 		/// </summary>
-		VertexId               = 0x0000000004000000,
+		VertexId               = 0x0000000008000000,
 	
 		/// <summary>
 		/// Viewport layer is available in vertex shader.
 		/// </summary>
-		ViewportLayerArray     = 0x0000000008000000,
+		ViewportLayerArray     = 0x0000000010000000,
 	
 		/// <summary>
 		/// All texture compare modes are supported.
 		/// </summary>
-		TextureCompareAll      = 0x0000000000180000,
+		TextureCompareAll      = 0x0000000000300000,
 	}
 	
 	[AllowDuplicates]

bindings/cs/bgfx.cs

@@ -996,6 +996,11 @@ public static partial class bgfx
 		/// Suspend rendering.
 		/// </summary>
 		Suspend                = 0x00080000,
+	
+		/// <summary>
+		/// Transparent backbuffer. Availability depends on: `BGFX_CAPS_TRANSPARENT_BACKBUFFER`.
+		/// </summary>
+		TransparentBackbuffer  = 0x00100000,
 		FullscreenShift        = 0,
 		FullscreenMask         = 0x00000001,
 		ReservedShift          = 31,
@@ -1099,52 +1104,57 @@ public static partial class bgfx
 		/// Texture blit is supported.
 		/// </summary>
 		TextureBlit            = 0x0000000000040000,
-		TextureCompareReserved = 0x0000000000080000,
+	
+		/// <summary>
+		/// Transparent back buffer supported.
+		/// </summary>
+		TransparentBackbuffer  = 0x0000000000080000,
+		TextureCompareReserved = 0x0000000000100000,
 	
 		/// <summary>
 		/// Texture compare less equal mode is supported.
 		/// </summary>
-		TextureCompareLequal   = 0x0000000000100000,
+		TextureCompareLequal   = 0x0000000000200000,
 	
 		/// <summary>
 		/// Cubemap texture array is supported.
 		/// </summary>
-		TextureCubeArray       = 0x0000000000200000,
+		TextureCubeArray       = 0x0000000000400000,
 	
 		/// <summary>
 		/// CPU direct access to GPU texture memory.
 		/// </summary>
-		TextureDirectAccess    = 0x0000000000400000,
+		TextureDirectAccess    = 0x0000000000800000,
 	
 		/// <summary>
 		/// Read-back texture is supported.
 		/// </summary>
-		TextureReadBack        = 0x0000000000800000,
+		TextureReadBack        = 0x0000000001000000,
 	
 		/// <summary>
 		/// Vertex attribute half-float is supported.
 		/// </summary>
-		VertexAttribHalf       = 0x0000000001000000,
+		VertexAttribHalf       = 0x0000000002000000,
 	
 		/// <summary>
 		/// Vertex attribute 10_10_10_2 is supported.
 		/// </summary>
-		VertexAttribUint10     = 0x0000000002000000,
+		VertexAttribUint10     = 0x0000000004000000,
 	
 		/// <summary>
 		/// Rendering with VertexID only is supported.
 		/// </summary>
-		VertexId               = 0x0000000004000000,
+		VertexId               = 0x0000000008000000,
 	
 		/// <summary>
 		/// Viewport layer is available in vertex shader.
 		/// </summary>
-		ViewportLayerArray     = 0x0000000008000000,
+		ViewportLayerArray     = 0x0000000010000000,
 	
 		/// <summary>
 		/// All texture compare modes are supported.
 		/// </summary>
-		TextureCompareAll      = 0x0000000000180000,
+		TextureCompareAll      = 0x0000000000300000,
 	}
 	
 	[Flags]

bindings/d/types.d

@@ -373,6 +373,7 @@ enum uint BGFX_RESET_HDR10 = 0x00010000; /// Enable HDR10 rendering.
 enum uint BGFX_RESET_HIDPI = 0x00020000; /// Enable HiDPI rendering.
 enum uint BGFX_RESET_DEPTH_CLAMP = 0x00040000; /// Enable depth clamp.
 enum uint BGFX_RESET_SUSPEND = 0x00080000; /// Suspend rendering.
+enum uint BGFX_RESET_TRANSPARENT_BACKBUFFER = 0x00100000; /// Transparent backbuffer. Availability depends on: `BGFX_CAPS_TRANSPARENT_BACKBUFFER`.
 
 enum uint BGFX_RESET_FULLSCREEN_SHIFT = 0;
 enum uint BGFX_RESET_FULLSCREEN_MASK = 0x00000001;
@@ -399,16 +400,17 @@ enum ulong BGFX_CAPS_SWAP_CHAIN = 0x0000000000008000; /// Multiple windows are s
 enum ulong BGFX_CAPS_TEXTURE_2D_ARRAY = 0x0000000000010000; /// 2D texture array is supported.
 enum ulong BGFX_CAPS_TEXTURE_3D = 0x0000000000020000; /// 3D textures are supported.
 enum ulong BGFX_CAPS_TEXTURE_BLIT = 0x0000000000040000; /// Texture blit is supported.
-enum ulong BGFX_CAPS_TEXTURE_COMPARE_RESERVED = 0x0000000000080000;
-enum ulong BGFX_CAPS_TEXTURE_COMPARE_LEQUAL = 0x0000000000100000; /// Texture compare less equal mode is supported.
-enum ulong BGFX_CAPS_TEXTURE_CUBE_ARRAY = 0x0000000000200000; /// Cubemap texture array is supported.
-enum ulong BGFX_CAPS_TEXTURE_DIRECT_ACCESS = 0x0000000000400000; /// CPU direct access to GPU texture memory.
-enum ulong BGFX_CAPS_TEXTURE_READ_BACK = 0x0000000000800000; /// Read-back texture is supported.
-enum ulong BGFX_CAPS_VERTEX_ATTRIB_HALF = 0x0000000001000000; /// Vertex attribute half-float is supported.
-enum ulong BGFX_CAPS_VERTEX_ATTRIB_UINT10 = 0x0000000002000000; /// Vertex attribute 10_10_10_2 is supported.
-enum ulong BGFX_CAPS_VERTEX_ID = 0x0000000004000000; /// Rendering with VertexID only is supported.
-enum ulong BGFX_CAPS_VIEWPORT_LAYER_ARRAY = 0x0000000008000000; /// Viewport layer is available in vertex shader.
-enum ulong BGFX_CAPS_TEXTURE_COMPARE_ALL = 0x0000000000180000; /// All texture compare modes are supported.
+enum ulong BGFX_CAPS_TRANSPARENT_BACKBUFFER = 0x0000000000080000; /// Transparent back buffer supported.
+enum ulong BGFX_CAPS_TEXTURE_COMPARE_RESERVED = 0x0000000000100000;
+enum ulong BGFX_CAPS_TEXTURE_COMPARE_LEQUAL = 0x0000000000200000; /// Texture compare less equal mode is supported.
+enum ulong BGFX_CAPS_TEXTURE_CUBE_ARRAY = 0x0000000000400000; /// Cubemap texture array is supported.
+enum ulong BGFX_CAPS_TEXTURE_DIRECT_ACCESS = 0x0000000000800000; /// CPU direct access to GPU texture memory.
+enum ulong BGFX_CAPS_TEXTURE_READ_BACK = 0x0000000001000000; /// Read-back texture is supported.
+enum ulong BGFX_CAPS_VERTEX_ATTRIB_HALF = 0x0000000002000000; /// Vertex attribute half-float is supported.
+enum ulong BGFX_CAPS_VERTEX_ATTRIB_UINT10 = 0x0000000004000000; /// Vertex attribute 10_10_10_2 is supported.
+enum ulong BGFX_CAPS_VERTEX_ID = 0x0000000008000000; /// Rendering with VertexID only is supported.
+enum ulong BGFX_CAPS_VIEWPORT_LAYER_ARRAY = 0x0000000010000000; /// Viewport layer is available in vertex shader.
+enum ulong BGFX_CAPS_TEXTURE_COMPARE_ALL = 0x0000000000300000; /// All texture compare modes are supported.
 
 enum uint BGFX_CAPS_FORMAT_TEXTURE_NONE = 0x00000000; /// Texture format is not supported.
 enum uint BGFX_CAPS_FORMAT_TEXTURE_2D = 0x00000001; /// Texture format is supported.

bindings/zig/bgfx.zig

@@ -617,6 +617,9 @@ pub const ResetFlags_DepthClamp: ResetFlags             = 0x00040000;
 
 /// Suspend rendering.
 pub const ResetFlags_Suspend: ResetFlags                = 0x00080000;
+
+/// Transparent backbuffer. Availability depends on: `BGFX_CAPS_TRANSPARENT_BACKBUFFER`.
+pub const ResetFlags_TransparentBackbuffer: ResetFlags  = 0x00100000;
 pub const ResetFlags_FullscreenShift: ResetFlags        = 0;
 pub const ResetFlags_FullscreenMask: ResetFlags         = 0x00000001;
 pub const ResetFlags_ReservedShift: ResetFlags          = 31;
@@ -679,34 +682,37 @@ pub const CapsFlags_Texture3D: CapsFlags              = 0x0000000000020000;
 
 /// Texture blit is supported.
 pub const CapsFlags_TextureBlit: CapsFlags            = 0x0000000000040000;
-pub const CapsFlags_TextureCompareReserved: CapsFlags = 0x0000000000080000;
+
+/// Transparent back buffer supported.
+pub const CapsFlags_TransparentBackbuffer: CapsFlags  = 0x0000000000080000;
+pub const CapsFlags_TextureCompareReserved: CapsFlags = 0x0000000000100000;
 
 /// Texture compare less equal mode is supported.
-pub const CapsFlags_TextureCompareLequal: CapsFlags   = 0x0000000000100000;
+pub const CapsFlags_TextureCompareLequal: CapsFlags   = 0x0000000000200000;
 
 /// Cubemap texture array is supported.
-pub const CapsFlags_TextureCubeArray: CapsFlags       = 0x0000000000200000;
+pub const CapsFlags_TextureCubeArray: CapsFlags       = 0x0000000000400000;
 
 /// CPU direct access to GPU texture memory.
-pub const CapsFlags_TextureDirectAccess: CapsFlags    = 0x0000000000400000;
+pub const CapsFlags_TextureDirectAccess: CapsFlags    = 0x0000000000800000;
 
 /// Read-back texture is supported.
-pub const CapsFlags_TextureReadBack: CapsFlags        = 0x0000000000800000;
+pub const CapsFlags_TextureReadBack: CapsFlags        = 0x0000000001000000;
 
 /// Vertex attribute half-float is supported.
-pub const CapsFlags_VertexAttribHalf: CapsFlags       = 0x0000000001000000;
+pub const CapsFlags_VertexAttribHalf: CapsFlags       = 0x0000000002000000;
 
 /// Vertex attribute 10_10_10_2 is supported.
-pub const CapsFlags_VertexAttribUint10: CapsFlags     = 0x0000000002000000;
+pub const CapsFlags_VertexAttribUint10: CapsFlags     = 0x0000000004000000;
 
 /// Rendering with VertexID only is supported.
-pub const CapsFlags_VertexId: CapsFlags               = 0x0000000004000000;
+pub const CapsFlags_VertexId: CapsFlags               = 0x0000000008000000;
 
 /// Viewport layer is available in vertex shader.
-pub const CapsFlags_ViewportLayerArray: CapsFlags     = 0x0000000008000000;
+pub const CapsFlags_ViewportLayerArray: CapsFlags     = 0x0000000010000000;
 
 /// All texture compare modes are supported.
-pub const CapsFlags_TextureCompareAll: CapsFlags      = 0x0000000000180000;
+pub const CapsFlags_TextureCompareAll: CapsFlags      = 0x0000000000300000;
 
 pub const CapsFormatFlags = u32;
 /// Texture format is not supported.

include/bgfx/defines.h

@@ -453,6 +453,7 @@
 #define BGFX_RESET_HIDPI                          UINT32_C(0x00020000) //!< Enable HiDPI rendering.
 #define BGFX_RESET_DEPTH_CLAMP                    UINT32_C(0x00040000) //!< Enable depth clamp.
 #define BGFX_RESET_SUSPEND                        UINT32_C(0x00080000) //!< Suspend rendering.
+#define BGFX_RESET_TRANSPARENT_BACKBUFFER         UINT32_C(0x00100000) //!< Transparent backbuffer. Availability depends on: `BGFX_CAPS_TRANSPARENT_BACKBUFFER`.
 
 #define BGFX_RESET_FULLSCREEN_SHIFT               0
 
@@ -480,15 +481,16 @@
 #define BGFX_CAPS_TEXTURE_2D_ARRAY                UINT64_C(0x0000000000010000) //!< 2D texture array is supported.
 #define BGFX_CAPS_TEXTURE_3D                      UINT64_C(0x0000000000020000) //!< 3D textures are supported.
 #define BGFX_CAPS_TEXTURE_BLIT                    UINT64_C(0x0000000000040000) //!< Texture blit is supported.
-#define BGFX_CAPS_TEXTURE_COMPARE_RESERVED        UINT64_C(0x0000000000080000)
-#define BGFX_CAPS_TEXTURE_COMPARE_LEQUAL          UINT64_C(0x0000000000100000) //!< Texture compare less equal mode is supported.
-#define BGFX_CAPS_TEXTURE_CUBE_ARRAY              UINT64_C(0x0000000000200000) //!< Cubemap texture array is supported.
-#define BGFX_CAPS_TEXTURE_DIRECT_ACCESS           UINT64_C(0x0000000000400000) //!< CPU direct access to GPU texture memory.
-#define BGFX_CAPS_TEXTURE_READ_BACK               UINT64_C(0x0000000000800000) //!< Read-back texture is supported.
-#define BGFX_CAPS_VERTEX_ATTRIB_HALF              UINT64_C(0x0000000001000000) //!< Vertex attribute half-float is supported.
-#define BGFX_CAPS_VERTEX_ATTRIB_UINT10            UINT64_C(0x0000000002000000) //!< Vertex attribute 10_10_10_2 is supported.
-#define BGFX_CAPS_VERTEX_ID                       UINT64_C(0x0000000004000000) //!< Rendering with VertexID only is supported.
-#define BGFX_CAPS_VIEWPORT_LAYER_ARRAY            UINT64_C(0x0000000008000000) //!< Viewport layer is available in vertex shader.
+#define BGFX_CAPS_TRANSPARENT_BACKBUFFER          UINT64_C(0x0000000000080000) //!< Transparent back buffer supported.
+#define BGFX_CAPS_TEXTURE_COMPARE_RESERVED        UINT64_C(0x0000000000100000)
+#define BGFX_CAPS_TEXTURE_COMPARE_LEQUAL          UINT64_C(0x0000000000200000) //!< Texture compare less equal mode is supported.
+#define BGFX_CAPS_TEXTURE_CUBE_ARRAY              UINT64_C(0x0000000000400000) //!< Cubemap texture array is supported.
+#define BGFX_CAPS_TEXTURE_DIRECT_ACCESS           UINT64_C(0x0000000000800000) //!< CPU direct access to GPU texture memory.
+#define BGFX_CAPS_TEXTURE_READ_BACK               UINT64_C(0x0000000001000000) //!< Read-back texture is supported.
+#define BGFX_CAPS_VERTEX_ATTRIB_HALF              UINT64_C(0x0000000002000000) //!< Vertex attribute half-float is supported.
+#define BGFX_CAPS_VERTEX_ATTRIB_UINT10            UINT64_C(0x0000000004000000) //!< Vertex attribute 10_10_10_2 is supported.
+#define BGFX_CAPS_VERTEX_ID                       UINT64_C(0x0000000008000000) //!< Rendering with VertexID only is supported.
+#define BGFX_CAPS_VIEWPORT_LAYER_ARRAY            UINT64_C(0x0000000010000000) //!< Viewport layer is available in vertex shader.
 /// All texture compare modes are supported.
 #define BGFX_CAPS_TEXTURE_COMPARE_ALL (0 \
 	| BGFX_CAPS_TEXTURE_COMPARE_RESERVED \

scripts/bgfx.idl

@@ -343,19 +343,20 @@ flag.ResetMsaa { bits = 32, shift = 4, range = 3, base = 1 }
 	()
 
 flag.Reset { bits = 32 }
-	.None             ( 0) --- No reset flags.
-	.Fullscreen       ( 1) --- Not supported yet.
-	.Vsync            ( 8) --- Enable V-Sync.
-	.Maxanisotropy    ( 9) --- Turn on/off max anisotropy.
-	.Capture          (10) --- Begin screen capture.
-	.FlushAfterRender (14) --- Flush rendering after submitting to GPU.
-	.FlipAfterRender  (15) --- This flag specifies where flip occurs. Default behaviour is that flip occurs
-	                       --- before rendering new frame. This flag only has effect when `BGFX_CONFIG_MULTITHREADED=0`.
-	.SrgbBackbuffer   (16) --- Enable sRGB backbuffer.
-	.Hdr10            (17) --- Enable HDR10 rendering.
-	.Hidpi            (18) --- Enable HiDPI rendering.
-	.DepthClamp       (19) --- Enable depth clamp.
-	.Suspend          (20) --- Suspend rendering.
+	.None                     ( 0) --- No reset flags.
+	.Fullscreen               ( 1) --- Not supported yet.
+	.Vsync                    ( 8) --- Enable V-Sync.
+	.Maxanisotropy            ( 9) --- Turn on/off max anisotropy.
+	.Capture                  (10) --- Begin screen capture.
+	.FlushAfterRender         (14) --- Flush rendering after submitting to GPU.
+	.FlipAfterRender          (15) --- This flag specifies where flip occurs. Default behaviour is that flip occurs
+	                               --- before rendering new frame. This flag only has effect when `BGFX_CONFIG_MULTITHREADED=0`.
+	.SrgbBackbuffer           (16) --- Enable sRGB backbuffer.
+	.Hdr10                    (17) --- Enable HDR10 rendering.
+	.Hidpi                    (18) --- Enable HiDPI rendering.
+	.DepthClamp               (19) --- Enable depth clamp.
+	.Suspend                  (20) --- Suspend rendering.
+	.TransparentBackbuffer    (21) --- Transparent backbuffer. Availability depends on: `BGFX_CAPS_TRANSPARENT_BACKBUFFER`.
 	()
 
 flag.ResetFullscreen { bits = 32, shift = 0, range = 1, base = 1 }
@@ -383,6 +384,7 @@ flag.Caps { bits = 64, base = 1, name = "Caps" }
 	.Texture_2dArray        --- 2D texture array is supported.
 	.Texture_3d             --- 3D textures are supported.
 	.TextureBlit            --- Texture blit is supported.
+	.TransparentBackbuffer  --- Transparent back buffer supported.
 	.TextureCompareReserved
 	.TextureCompareLequal   --- Texture compare less equal mode is supported.
 	.TextureCubeArray       --- Cubemap texture array is supported.

src/dxgi.cpp

@@ -308,6 +308,7 @@ namespace bgfx
 				}
 
 				_caps.supported |= hdr10 ? BGFX_CAPS_HDR10 : 0;
+				_caps.supported |= BX_ENABLED(BX_PLATFORM_WINRT) ? BGFX_CAPS_TRANSPARENT_BACKBUFFER : 0;
 
 				DX_RELEASE(adapter, adapter == m_adapter ? 1 : 0);
 			}

src/renderer_d3d11.cpp

@@ -1035,7 +1035,9 @@ namespace bgfx { namespace d3d11
 						: DXGI_SCALING_STRETCH
 						;
 					m_scd.swapEffect = m_swapEffect;
-					m_scd.alphaMode  = DXGI_ALPHA_MODE_IGNORE;
+
+					m_scd.alphaMode = (_init.resolution.reset & BGFX_RESET_TRANSPARENT_BACKBUFFER) ? DXGI_ALPHA_MODE_PREMULTIPLIED : DXGI_ALPHA_MODE_IGNORE;
+
 					m_scd.flags = DXGI_SWAP_CHAIN_FLAG_ALLOW_MODE_SWITCH;
 
 					m_scd.maxFrameLatency = bx::min<uint8_t>(_init.resolution.maxFrameLatency, BGFX_CONFIG_MAX_FRAME_LATENCY);
@@ -3425,6 +3427,50 @@ namespace bgfx { namespace d3d11
 			}
 		}
 
+		void premultiplyBackBuffer(const ClearQuad& _clearQuad)
+		{
+			ID3D11DeviceContext* deviceCtx = m_deviceCtx;
+
+			uint64_t state = 0;
+			state |= BGFX_STATE_WRITE_RGB;
+			state |= BGFX_STATE_DEPTH_TEST_ALWAYS;
+			state |= BGFX_STATE_BLEND_FUNC_SEPARATE(BGFX_STATE_BLEND_DST_COLOR, BGFX_STATE_BLEND_DST_ALPHA, BGFX_STATE_BLEND_DST_ALPHA, BGFX_STATE_BLEND_ZERO);
+
+			uint64_t stencil = 0;
+
+			setBlendState(state);
+			setDepthStencilState(state, stencil);
+			setRasterizerState(state);
+
+			uint32_t numMrt = 1;
+			if (isValid(_clearQuad.m_program[numMrt-1]))
+			{
+				ProgramD3D11& program = m_program[_clearQuad.m_program[numMrt-1].idx];
+				m_currentProgram = &program;
+
+				const ShaderD3D11* vsh = program.m_vsh;
+				deviceCtx->VSSetShader(vsh->m_vertexShader, NULL, 0);
+				deviceCtx->VSSetConstantBuffers(0, 1, &vsh->m_buffer);
+
+				const ShaderD3D11* fsh = program.m_fsh;
+				deviceCtx->PSSetShader(fsh->m_pixelShader, NULL, 0);
+
+				VertexBufferD3D11& vb = m_vertexBuffers[_clearQuad.m_vb.idx];
+				const VertexLayout& layout = _clearQuad.m_layout;
+
+				const uint32_t stride = layout.m_stride;
+				const uint32_t offset = 0;
+
+				deviceCtx->IASetVertexBuffers(0, 1, &vb.m_ptr, &stride, &offset);
+				setInputLayout(layout, program, 0);
+
+				m_deviceCtx->OMSetRenderTargets(1, &m_backBufferColor, m_backBufferDepthStencil);
+
+				deviceCtx->IASetPrimitiveTopology(D3D11_PRIMITIVE_TOPOLOGY_TRIANGLESTRIP);
+				deviceCtx->Draw(4, 0);
+			}
+		}
+
 		void clearQuad(ClearQuad& _clearQuad, const Rect& _rect, const Clear& _clear, const float _palette[][4])
 		{
 			uint32_t width;
@@ -6626,6 +6672,11 @@ namespace bgfx { namespace d3d11
 			BGFX_D3D11_PROFILER_END();
 		}
 
+		if (m_resolution.reset & BGFX_RESET_TRANSPARENT_BACKBUFFER)
+		{
+			premultiplyBackBuffer(_clearQuad);
+		}
+
 		m_deviceCtx->OMSetRenderTargets(1, s_zero.m_rtv, NULL);
 
 		if (NULL != m_msaaRt)

src/renderer_gl.cpp

@@ -3028,6 +3028,8 @@ namespace bgfx { namespace gl
 					: 0
 					;
 
+				g_caps.supported |= BX_ENABLED(BX_PLATFORM_WINRT) ? BGFX_CAPS_TRANSPARENT_BACKBUFFER : 0;
+
 				if (s_extension[Extension::ARB_debug_output].m_supported
 				||  s_extension[Extension::KHR_debug].m_supported)
 				{
@@ -3577,7 +3579,7 @@ namespace bgfx { namespace gl
 		void submitBlit(BlitState& _bs, uint16_t _view);
 
 		void submit(Frame* _render, ClearQuad& _clearQuad, TextVideoMemBlitter& _textVideoMemBlitter) override;
-
+		void premultiplyBackBuffer(const ClearQuad& _clearQuad);
 		void blitSetup(TextVideoMemBlitter& _blitter) override
 		{
 			if (0 != m_vao)
@@ -7374,6 +7376,39 @@ namespace bgfx { namespace gl
 		}
 	}
 
+	void RendererContextGL::premultiplyBackBuffer(const ClearQuad& _clearQuad)
+	{
+		const uint32_t numMrt = 1;
+		if (isValid(_clearQuad.m_program[numMrt - 1]))
+		{
+			GL_CHECK(glDisable(GL_SCISSOR_TEST));
+			GL_CHECK(glDisable(GL_CULL_FACE));
+			GL_CHECK(glEnable(GL_BLEND));
+			GL_CHECK(glEnable(GL_BLEND));
+			GL_CHECK(glBlendFuncSeparate(GL_DST_COLOR, GL_DST_ALPHA, GL_DST_ALPHA, GL_ZERO));
+
+			GL_CHECK(glColorMask(true, true, true, false));
+			GL_CHECK(glDisable(GL_DEPTH_TEST));
+			GL_CHECK(glDisable(GL_STENCIL_TEST));
+
+			const VertexBufferGL& vb = m_vertexBuffers[_clearQuad.m_vb.idx];
+			const VertexLayout& layout = _clearQuad.m_layout;
+
+			GL_CHECK(glBindBuffer(GL_ARRAY_BUFFER, vb.m_id));
+
+			ProgramGL& program = m_program[_clearQuad.m_program[numMrt - 1].idx];
+			setProgram(program.m_id);
+			program.bindAttributesBegin();
+			program.bindAttributes(layout, 0);
+			program.bindAttributesEnd();
+
+			GL_CHECK(glDrawArrays(GL_TRIANGLE_STRIP
+				, 0
+				, 4
+			));
+		}
+	}
+
 	void RendererContextGL::submit(Frame* _render, ClearQuad& _clearQuad, TextVideoMemBlitter& _textVideoMemBlitter)
 	{
 		if (_render->m_capture)
@@ -8461,6 +8496,11 @@ namespace bgfx { namespace gl
 			}
 		}
 
+		if (m_resolution.reset & BGFX_RESET_TRANSPARENT_BACKBUFFER)
+		{
+			premultiplyBackBuffer(_clearQuad);
+		}
+
 		BGFX_GL_PROFILER_END();
 
 		m_glctx.makeCurrent(NULL);