GPU: Simultaneous compute pass read-write

include/SDL3/SDL_gpu.h

@@ -464,18 +464,19 @@ typedef enum SDL_GPUTextureFormat
  * A texture must have at least one usage flag. Note that some usage flag
  * combinations are invalid.
  *
- * \since This enum is available since SDL 3.0.0
+ * \since This datatype is available since SDL 3.0.0
  *
  * \sa SDL_CreateGPUTexture
  */
 typedef Uint32 SDL_GPUTextureUsageFlags;
 
-#define SDL_GPU_TEXTUREUSAGE_SAMPLER               (1u << 0) /**< Texture supports sampling. */
-#define SDL_GPU_TEXTUREUSAGE_COLOR_TARGET          (1u << 1) /**< Texture is a color render target. */
-#define SDL_GPU_TEXTUREUSAGE_DEPTH_STENCIL_TARGET  (1u << 2) /**< Texture is a depth stencil target. */
-#define SDL_GPU_TEXTUREUSAGE_GRAPHICS_STORAGE_READ (1u << 3) /**< Texture supports storage reads in graphics stages. */
-#define SDL_GPU_TEXTUREUSAGE_COMPUTE_STORAGE_READ  (1u << 4) /**< Texture supports storage reads in the compute stage. */
-#define SDL_GPU_TEXTUREUSAGE_COMPUTE_STORAGE_WRITE (1u << 5) /**< Texture supports storage writes in the compute stage. */
+#define SDL_GPU_TEXTUREUSAGE_SAMPLER                                 (1u << 0) /**< Texture supports sampling. */
+#define SDL_GPU_TEXTUREUSAGE_COLOR_TARGET                            (1u << 1) /**< Texture is a color render target. */
+#define SDL_GPU_TEXTUREUSAGE_DEPTH_STENCIL_TARGET                    (1u << 2) /**< Texture is a depth stencil target. */
+#define SDL_GPU_TEXTUREUSAGE_GRAPHICS_STORAGE_READ                   (1u << 3) /**< Texture supports storage reads in graphics stages. */
+#define SDL_GPU_TEXTUREUSAGE_COMPUTE_STORAGE_READ                    (1u << 4) /**< Texture supports storage reads in the compute stage. */
+#define SDL_GPU_TEXTUREUSAGE_COMPUTE_STORAGE_WRITE                   (1u << 5) /**< Texture supports storage writes in the compute stage. */
+#define SDL_GPU_TEXTUREUSAGE_COMPUTE_STORAGE_SIMULTANEOUS_READ_WRITE (1u << 6) /**< Texture supports reads and writes in the same compute shader. This is NOT equivalent to READ | WRITE. */
 
 /**
  * Specifies the type of a texture.
@@ -536,18 +537,18 @@ typedef enum SDL_GPUCubeMapFace
  * A buffer must have at least one usage flag. Note that some usage flag
  * combinations are invalid.
  *
- * \since This enum is available since SDL 3.0.0
+ * \since This datatype is available since SDL 3.0.0
  *
  * \sa SDL_CreateGPUBuffer
  */
 typedef Uint32 SDL_GPUBufferUsageFlags;
 
-#define SDL_GPU_BUFFERUSAGE_VERTEX                (1u << 0) /**< Buffer is a vertex buffer. */
-#define SDL_GPU_BUFFERUSAGE_INDEX                 (1u << 1) /**< Buffer is an index buffer. */
-#define SDL_GPU_BUFFERUSAGE_INDIRECT              (1u << 2) /**< Buffer is an indirect buffer. */
-#define SDL_GPU_BUFFERUSAGE_GRAPHICS_STORAGE_READ (1u << 3) /**< Buffer supports storage reads in graphics stages. */
-#define SDL_GPU_BUFFERUSAGE_COMPUTE_STORAGE_READ  (1u << 4) /**< Buffer supports storage reads in the compute stage. */
-#define SDL_GPU_BUFFERUSAGE_COMPUTE_STORAGE_WRITE (1u << 5) /**< Buffer supports storage writes in the compute stage. */
+#define SDL_GPU_BUFFERUSAGE_VERTEX                                  (1u << 0) /**< Buffer is a vertex buffer. */
+#define SDL_GPU_BUFFERUSAGE_INDEX                                   (1u << 1) /**< Buffer is an index buffer. */
+#define SDL_GPU_BUFFERUSAGE_INDIRECT                                (1u << 2) /**< Buffer is an indirect buffer. */
+#define SDL_GPU_BUFFERUSAGE_GRAPHICS_STORAGE_READ                   (1u << 3) /**< Buffer supports storage reads in graphics stages. */
+#define SDL_GPU_BUFFERUSAGE_COMPUTE_STORAGE_READ                    (1u << 4) /**< Buffer supports storage reads in the compute stage. */
+#define SDL_GPU_BUFFERUSAGE_COMPUTE_STORAGE_WRITE                   (1u << 5) /**< Buffer supports storage writes in the compute stage. */
 
 /**
  * Specifies how a transfer buffer is intended to be used by the client.
@@ -811,7 +812,7 @@ typedef enum SDL_GPUBlendFactor
 /**
  * Specifies which color components are written in a graphics pipeline.
  *
- * \since This enum is available since SDL 3.0.0
+ * \since This datatype is available since SDL 3.0.0
  *
  * \sa SDL_CreateGPUGraphicsPipeline
  */
@@ -1489,8 +1490,8 @@ typedef struct SDL_GPUComputePipelineCreateInfo
     Uint32 num_samplers;                    /**< The number of samplers defined in the shader. */
     Uint32 num_readonly_storage_textures;   /**< The number of readonly storage textures defined in the shader. */
     Uint32 num_readonly_storage_buffers;    /**< The number of readonly storage buffers defined in the shader. */
-    Uint32 num_writeonly_storage_textures;  /**< The number of writeonly storage textures defined in the shader. */
-    Uint32 num_writeonly_storage_buffers;   /**< The number of writeonly storage buffers defined in the shader. */
+    Uint32 num_readwrite_storage_textures;  /**< The number of read-write storage textures defined in the shader. */
+    Uint32 num_readwrite_storage_buffers;   /**< The number of read-write storage buffers defined in the shader. */
     Uint32 num_uniform_buffers;             /**< The number of uniform buffers defined in the shader. */
     Uint32 threadcount_x;                   /**< The number of threads in the X dimension. This should match the value in the shader. */
     Uint32 threadcount_y;                   /**< The number of threads in the Y dimension. This should match the value in the shader. */
@@ -1667,14 +1668,14 @@ typedef struct SDL_GPUTextureSamplerBinding
  *
  * \sa SDL_BeginGPUComputePass
  */
-typedef struct SDL_GPUStorageBufferWriteOnlyBinding
+typedef struct SDL_GPUStorageBufferReadWriteBinding
 {
     SDL_GPUBuffer *buffer;  /**< The buffer to bind. Must have been created with SDL_GPU_BUFFERUSAGE_COMPUTE_STORAGE_WRITE. */
     bool cycle;         /**< true cycles the buffer if it is already bound. */
     Uint8 padding1;
     Uint8 padding2;
     Uint8 padding3;
-} SDL_GPUStorageBufferWriteOnlyBinding;
+} SDL_GPUStorageBufferReadWriteBinding;
 
 /**
  * A structure specifying parameters related to binding textures in a compute
@@ -1684,7 +1685,7 @@ typedef struct SDL_GPUStorageBufferWriteOnlyBinding
  *
  * \sa SDL_BeginGPUComputePass
  */
-typedef struct SDL_GPUStorageTextureWriteOnlyBinding
+typedef struct SDL_GPUStorageTextureReadWriteBinding
 {
     SDL_GPUTexture *texture;  /**< The texture to bind. Must have been created with SDL_GPU_TEXTUREUSAGE_COMPUTE_STORAGE_WRITE. */
     Uint32 mip_level;         /**< The mip level index to bind. */
@@ -1693,7 +1694,7 @@ typedef struct SDL_GPUStorageTextureWriteOnlyBinding
     Uint8 padding1;
     Uint8 padding2;
     Uint8 padding3;
-} SDL_GPUStorageTextureWriteOnlyBinding;
+} SDL_GPUStorageTextureReadWriteBinding;
 
 /* Functions */
 
@@ -2807,15 +2808,17 @@ extern SDL_DECLSPEC void SDLCALL SDL_EndGPURenderPass(
  * Begins a compute pass on a command buffer.
  *
  * A compute pass is defined by a set of texture subresources and buffers that
- * will be written to by compute pipelines. These textures and buffers must
- * have been created with the COMPUTE_STORAGE_WRITE bit. All operations
+ * may be written to by compute pipelines. These textures and buffers must
+ * have been created with the COMPUTE_STORAGE_WRITE bit or the COMPUTE_STORAGE_SIMULTANEOUS_READ_WRITE bit. All operations
  * related to compute pipelines must take place inside of a compute pass. You
  * must not begin another compute pass, or a render pass or copy pass before
  * ending the compute pass.
  *
- * A VERY IMPORTANT NOTE Textures and buffers bound as write-only MUST NOT be
- * read from during the compute pass. Doing so will result in undefined
- * behavior. If your compute work requires reading the output from a previous
+ * A VERY IMPORTANT NOTE - Reads and writes in compute shaders are NOT implicitly synchronized.
+ * This means you may cause data races by both reading and writing a resource in a compute pass.
+ * Reading and writing a texture in the same compute shader is only supported by specific texture formats.
+ * Make sure you check the format support!
+ * If your compute work requires reading the completed output from a previous
  * dispatch, you MUST end the current compute pass and begin a new one before
  * you can safely access the data.
  *
@@ -2836,9 +2839,9 @@ extern SDL_DECLSPEC void SDLCALL SDL_EndGPURenderPass(
  */
 extern SDL_DECLSPEC SDL_GPUComputePass *SDLCALL SDL_BeginGPUComputePass(
     SDL_GPUCommandBuffer *command_buffer,
-    const SDL_GPUStorageTextureWriteOnlyBinding *storage_texture_bindings,
+    const SDL_GPUStorageTextureReadWriteBinding *storage_texture_bindings,
     Uint32 num_storage_texture_bindings,
-    const SDL_GPUStorageBufferWriteOnlyBinding *storage_buffer_bindings,
+    const SDL_GPUStorageBufferReadWriteBinding *storage_buffer_bindings,
     Uint32 num_storage_buffer_bindings);
 
 /**

src/dynapi/SDL_dynapi_procs.h

@@ -63,7 +63,7 @@ SDL_DYNAPI_PROC(SDL_TimerID,SDL_AddTimerNS,(Uint64 a, SDL_NSTimerCallback b, voi
 SDL_DYNAPI_PROC(bool,SDL_AddVulkanRenderSemaphores,(SDL_Renderer *a, Uint32 b, Sint64 c, Sint64 d),(a,b,c,d),return)
 SDL_DYNAPI_PROC(SDL_JoystickID,SDL_AttachVirtualJoystick,(const SDL_VirtualJoystickDesc *a),(a),return)
 SDL_DYNAPI_PROC(bool,SDL_AudioDevicePaused,(SDL_AudioDeviceID a),(a),return)
-SDL_DYNAPI_PROC(SDL_GPUComputePass*,SDL_BeginGPUComputePass,(SDL_GPUCommandBuffer *a, const SDL_GPUStorageTextureWriteOnlyBinding *b, Uint32 c, const SDL_GPUStorageBufferWriteOnlyBinding *d, Uint32 e),(a,b,c,d,e),return)
+SDL_DYNAPI_PROC(SDL_GPUComputePass*,SDL_BeginGPUComputePass,(SDL_GPUCommandBuffer *a, const SDL_GPUStorageTextureReadWriteBinding *b, Uint32 c, const SDL_GPUStorageBufferReadWriteBinding *d, Uint32 e),(a,b,c,d,e),return)
 SDL_DYNAPI_PROC(SDL_GPUCopyPass*,SDL_BeginGPUCopyPass,(SDL_GPUCommandBuffer *a),(a),return)
 SDL_DYNAPI_PROC(SDL_GPURenderPass*,SDL_BeginGPURenderPass,(SDL_GPUCommandBuffer *a, const SDL_GPUColorTargetInfo *b, Uint32 c, const SDL_GPUDepthStencilTargetInfo *d),(a,b,c,d),return)
 SDL_DYNAPI_PROC(bool,SDL_BindAudioStream,(SDL_AudioDeviceID a, SDL_AudioStream *b),(a,b),return)

src/gpu/SDL_gpu.c

@@ -705,11 +705,11 @@ SDL_GPUComputePipeline *SDL_CreateGPUComputePipeline(
             SDL_assert_release(!"Incompatible shader format for GPU backend");
             return NULL;
         }
-        if (createinfo->num_writeonly_storage_textures > MAX_COMPUTE_WRITE_TEXTURES) {
+        if (createinfo->num_readwrite_storage_textures > MAX_COMPUTE_WRITE_TEXTURES) {
             SDL_assert_release(!"Compute pipeline write-only texture count cannot be higher than 8!");
             return NULL;
         }
-        if (createinfo->num_writeonly_storage_buffers > MAX_COMPUTE_WRITE_BUFFERS) {
+        if (createinfo->num_readwrite_storage_buffers > MAX_COMPUTE_WRITE_BUFFERS) {
             SDL_assert_release(!"Compute pipeline write-only buffer count cannot be higher than 8!");
             return NULL;
         }
@@ -1868,9 +1868,9 @@ void SDL_EndGPURenderPass(
 
 SDL_GPUComputePass *SDL_BeginGPUComputePass(
     SDL_GPUCommandBuffer *command_buffer,
-    const SDL_GPUStorageTextureWriteOnlyBinding *storage_texture_bindings,
+    const SDL_GPUStorageTextureReadWriteBinding *storage_texture_bindings,
     Uint32 num_storage_texture_bindings,
-    const SDL_GPUStorageBufferWriteOnlyBinding *storage_buffer_bindings,
+    const SDL_GPUStorageBufferReadWriteBinding *storage_buffer_bindings,
     Uint32 num_storage_buffer_bindings)
 {
     CommandBufferCommonHeader *commandBufferHeader;
@@ -1898,6 +1898,16 @@ SDL_GPUComputePass *SDL_BeginGPUComputePass(
     if (COMMAND_BUFFER_DEVICE->debug_mode) {
         CHECK_COMMAND_BUFFER_RETURN_NULL
         CHECK_ANY_PASS_IN_PROGRESS("Cannot begin compute pass during another pass!", NULL)
+
+        for (Uint32 i = 0; i < num_storage_texture_bindings; i += 1) {
+            TextureCommonHeader *header = (TextureCommonHeader *)storage_texture_bindings[i].texture;
+            if (!(header->info.usage & SDL_GPU_TEXTUREUSAGE_COMPUTE_STORAGE_WRITE) && !(header->info.usage & SDL_GPU_TEXTUREUSAGE_COMPUTE_STORAGE_SIMULTANEOUS_READ_WRITE)) {
+                SDL_assert_release(!"Texture must be created with COMPUTE_STORAGE_WRITE or COMPUTE_STORAGE_SIMULTANEOUS_READ_WRITE flag");
+                return NULL;
+            }
+        }
+
+        // TODO: validate buffer usage?
     }
 
     COMMAND_BUFFER_DEVICE->BeginComputePass(

src/gpu/SDL_sysgpu.h

@@ -503,9 +503,9 @@ struct SDL_GPUDevice
 
     void (*BeginComputePass)(
         SDL_GPUCommandBuffer *commandBuffer,
-        const SDL_GPUStorageTextureWriteOnlyBinding *storageTextureBindings,
+        const SDL_GPUStorageTextureReadWriteBinding *storageTextureBindings,
         Uint32 numStorageTextureBindings,
-        const SDL_GPUStorageBufferWriteOnlyBinding *storageBufferBindings,
+        const SDL_GPUStorageBufferReadWriteBinding *storageBufferBindings,
         Uint32 numStorageBufferBindings);
 
     void (*BindComputePipeline)(

src/gpu/d3d11/SDL_gpu_d3d11.c

@@ -529,9 +529,9 @@ typedef struct D3D11ComputePipeline
 
     Uint32 numSamplers;
     Uint32 numReadonlyStorageTextures;
-    Uint32 numWriteonlyStorageTextures;
+    Uint32 numReadWriteStorageTextures;
     Uint32 numReadonlyStorageBuffers;
-    Uint32 numWriteonlyStorageBuffers;
+    Uint32 numReadWriteStorageBuffers;
     Uint32 numUniformBuffers;
 } D3D11ComputePipeline;
 
@@ -687,8 +687,8 @@ typedef struct D3D11CommandBuffer
     D3D11Sampler *computeSamplers[MAX_TEXTURE_SAMPLERS_PER_STAGE];
     D3D11Texture *computeReadOnlyStorageTextures[MAX_STORAGE_TEXTURES_PER_STAGE];
     D3D11Buffer *computeReadOnlyStorageBuffers[MAX_STORAGE_BUFFERS_PER_STAGE];
-    D3D11TextureSubresource *computeWriteOnlyStorageTextureSubresources[MAX_COMPUTE_WRITE_TEXTURES];
-    D3D11Buffer *computeWriteOnlyStorageBuffers[MAX_COMPUTE_WRITE_BUFFERS];
+    D3D11TextureSubresource *computeReadWriteStorageTextureSubresources[MAX_COMPUTE_WRITE_TEXTURES];
+    D3D11Buffer *computeReadWriteStorageBuffers[MAX_COMPUTE_WRITE_BUFFERS];
 
     // Uniform buffers
     D3D11UniformBuffer *vertexUniformBuffers[MAX_UNIFORM_BUFFERS_PER_STAGE];
@@ -1524,9 +1524,9 @@ static SDL_GPUComputePipeline *D3D11_CreateComputePipeline(
     pipeline->computeShader = shader;
     pipeline->numSamplers = createinfo->num_samplers;
     pipeline->numReadonlyStorageTextures = createinfo->num_readonly_storage_textures;
-    pipeline->numWriteonlyStorageTextures = createinfo->num_writeonly_storage_textures;
+    pipeline->numReadWriteStorageTextures = createinfo->num_readwrite_storage_textures;
     pipeline->numReadonlyStorageBuffers = createinfo->num_readonly_storage_buffers;
-    pipeline->numWriteonlyStorageBuffers = createinfo->num_writeonly_storage_buffers;
+    pipeline->numReadWriteStorageBuffers = createinfo->num_readwrite_storage_buffers;
     pipeline->numUniformBuffers = createinfo->num_uniform_buffers;
     // thread counts are ignored in d3d11
 
@@ -3224,8 +3224,8 @@ static SDL_GPUCommandBuffer *D3D11_AcquireCommandBuffer(
     SDL_zeroa(commandBuffer->computeSamplerTextures);
     SDL_zeroa(commandBuffer->computeReadOnlyStorageTextures);
     SDL_zeroa(commandBuffer->computeReadOnlyStorageBuffers);
-    SDL_zeroa(commandBuffer->computeWriteOnlyStorageTextureSubresources);
-    SDL_zeroa(commandBuffer->computeWriteOnlyStorageBuffers);
+    SDL_zeroa(commandBuffer->computeReadWriteStorageTextureSubresources);
+    SDL_zeroa(commandBuffer->computeReadWriteStorageBuffers);
 
     bool acquireFenceResult = D3D11_INTERNAL_AcquireFence(commandBuffer);
     commandBuffer->autoReleaseFence = 1;
@@ -4284,9 +4284,9 @@ static void D3D11_Blit(
 
 static void D3D11_BeginComputePass(
     SDL_GPUCommandBuffer *commandBuffer,
-    const SDL_GPUStorageTextureWriteOnlyBinding *storageTextureBindings,
+    const SDL_GPUStorageTextureReadWriteBinding *storageTextureBindings,
     Uint32 numStorageTextureBindings,
-    const SDL_GPUStorageBufferWriteOnlyBinding *storageBufferBindings,
+    const SDL_GPUStorageBufferReadWriteBinding *storageBufferBindings,
     Uint32 numStorageBufferBindings)
 {
     D3D11CommandBuffer *d3d11CommandBuffer = (D3D11CommandBuffer *)commandBuffer;
@@ -4310,7 +4310,7 @@ static void D3D11_BeginComputePass(
             d3d11CommandBuffer,
             textureSubresource->parent);
 
-        d3d11CommandBuffer->computeWriteOnlyStorageTextureSubresources[i] = textureSubresource;
+        d3d11CommandBuffer->computeReadWriteStorageTextureSubresources[i] = textureSubresource;
     }
 
     for (Uint32 i = 0; i < numStorageBufferBindings; i += 1) {
@@ -4325,15 +4325,15 @@ static void D3D11_BeginComputePass(
             d3d11CommandBuffer,
             buffer);
 
-        d3d11CommandBuffer->computeWriteOnlyStorageBuffers[i] = buffer;
+        d3d11CommandBuffer->computeReadWriteStorageBuffers[i] = buffer;
     }
 
     for (Uint32 i = 0; i < numStorageTextureBindings; i += 1) {
-        uavs[i] = d3d11CommandBuffer->computeWriteOnlyStorageTextureSubresources[i]->uav;
+        uavs[i] = d3d11CommandBuffer->computeReadWriteStorageTextureSubresources[i]->uav;
     }
 
     for (Uint32 i = 0; i < numStorageBufferBindings; i += 1) {
-        uavs[numStorageTextureBindings + i] = d3d11CommandBuffer->computeWriteOnlyStorageBuffers[i]->uav;
+        uavs[numStorageTextureBindings + i] = d3d11CommandBuffer->computeReadWriteStorageBuffers[i]->uav;
     }
 
     ID3D11DeviceContext_CSSetUnorderedAccessViews(
@@ -4622,8 +4622,8 @@ static void D3D11_EndComputePass(
     SDL_zeroa(d3d11CommandBuffer->computeSamplerTextures);
     SDL_zeroa(d3d11CommandBuffer->computeReadOnlyStorageTextures);
     SDL_zeroa(d3d11CommandBuffer->computeReadOnlyStorageBuffers);
-    SDL_zeroa(d3d11CommandBuffer->computeWriteOnlyStorageTextureSubresources);
-    SDL_zeroa(d3d11CommandBuffer->computeWriteOnlyStorageBuffers);
+    SDL_zeroa(d3d11CommandBuffer->computeReadWriteStorageTextureSubresources);
+    SDL_zeroa(d3d11CommandBuffer->computeReadWriteStorageBuffers);
 }
 
 // Fence Cleanup
@@ -5763,6 +5763,7 @@ static bool D3D11_SupportsTextureFormat(
     DXGI_FORMAT dxgiFormat = SDLToD3D11_TextureFormat[format];
     DXGI_FORMAT typelessFormat = D3D11_INTERNAL_GetTypelessFormat(dxgiFormat);
     UINT formatSupport, sampleableFormatSupport;
+    D3D11_FEATURE_DATA_FORMAT_SUPPORT2 formatSupport2 = { dxgiFormat, 0 };
     HRESULT res;
 
     res = ID3D11Device_CheckFormatSupport(
@@ -5787,6 +5788,19 @@ static bool D3D11_SupportsTextureFormat(
         }
     }
 
+    // Checks for SIMULTANEOUS_READ_WRITE support
+    if (usage & SDL_GPU_TEXTUREUSAGE_COMPUTE_STORAGE_SIMULTANEOUS_READ_WRITE) {
+        res = ID3D11Device_CheckFeatureSupport(
+            renderer->device,
+            D3D11_FEATURE_FORMAT_SUPPORT2,
+            &formatSupport2,
+            sizeof(formatSupport2));
+        if (FAILED(res)) {
+            // Format is apparently unknown
+            return false;
+        }
+    }
+
     // Is the texture type supported?
     if (type == SDL_GPU_TEXTURETYPE_2D && !(formatSupport & D3D11_FORMAT_SUPPORT_TEXTURE2D)) {
         return false;
@@ -5815,6 +5829,9 @@ static bool D3D11_SupportsTextureFormat(
         // TYPED_UNORDERED_ACCESS_VIEW implies support for typed UAV stores
         return false;
     }
+    if ((usage & (SDL_GPU_TEXTUREUSAGE_COMPUTE_STORAGE_SIMULTANEOUS_READ_WRITE) && !(formatSupport2.OutFormatSupport2 & D3D11_FORMAT_SUPPORT2_UAV_TYPED_LOAD))) {
+        return false;
+    }
     if ((usage & SDL_GPU_TEXTUREUSAGE_COLOR_TARGET) && !(formatSupport & D3D11_FORMAT_SUPPORT_RENDER_TARGET)) {
         return false;
     }