GPUStorageBuf: Add `read()` function to readback buffer data to host

This is not expected to be fast. This is only for inspecting the content
of the buffer for debugging or validation purpose.

5 files changed, 31 insertions, 0 deletions

diff --git a/source/blender/gpu/GPU_storage_buffer.h b/source/blender/gpu/GPU_storage_buffer.h
index ca6a848786b..8837a7c7647 100644
--- a/source/blender/gpu/GPU_storage_buffer.h
+++ b/source/blender/gpu/GPU_storage_buffer.h
@@ -48,6 +48,13 @@ void GPU_storagebuf_clear(GPUStorageBuf *ssbo,
 void GPU_storagebuf_clear_to_zero(GPUStorageBuf *ssbo);
 
 /**
+ * Read back content of the buffer to CPU for inspection.
+ * Slow! Only use for inspection / debugging.
+ * NOTE: Not synchronized. Use appropriate barrier before reading.
+ */
+void GPU_storagebuf_read(GPUStorageBuf *ssbo, void *data);
+
+/**
  * \brief Copy a part of a vertex buffer to a storage buffer.
  *
  * \param ssbo: destination storage buffer
diff --git a/source/blender/gpu/intern/gpu_storage_buffer.cc b/source/blender/gpu/intern/gpu_storage_buffer.cc
index afa27da9c85..460a643089c 100644
--- a/source/blender/gpu/intern/gpu_storage_buffer.cc
+++ b/source/blender/gpu/intern/gpu_storage_buffer.cc
@@ -109,4 +109,9 @@ void GPU_storagebuf_copy_sub_from_vertbuf(
   unwrap(ssbo)->copy_sub(unwrap(src), dst_offset, src_offset, copy_size);
 }
 
+void GPU_storagebuf_read(GPUStorageBuf *ssbo, void *data)
+{
+  unwrap(ssbo)->read(data);
+}
+
 /** \} */
diff --git a/source/blender/gpu/intern/gpu_storage_buffer_private.hh b/source/blender/gpu/intern/gpu_storage_buffer_private.hh
index 9baec0c2a77..0c96f97ad30 100644
--- a/source/blender/gpu/intern/gpu_storage_buffer_private.hh
+++ b/source/blender/gpu/intern/gpu_storage_buffer_private.hh
@@ -44,6 +44,7 @@ class StorageBuf {
                      eGPUDataFormat data_format,
                      void *data) = 0;
   virtual void copy_sub(VertBuf *src, uint dst_offset, uint src_offset, uint copy_size) = 0;
+  virtual void read(void *data) = 0;
 };
 
 /* Syntactic sugar. */
diff --git a/source/blender/gpu/opengl/gl_storage_buffer.cc b/source/blender/gpu/opengl/gl_storage_buffer.cc
index 83a56edcf04..5d876308b3c 100644
--- a/source/blender/gpu/opengl/gl_storage_buffer.cc
+++ b/source/blender/gpu/opengl/gl_storage_buffer.cc
@@ -166,6 +166,23 @@ void GLStorageBuf::copy_sub(VertBuf *src_, uint dst_offset, uint src_offset, uin
   }
 }
 
+void GLStorageBuf::read(void *data)
+{
+  if (ssbo_id_ == 0) {
+    this->init();
+  }
+
+  if (GLContext::direct_state_access_support) {
+    glGetNamedBufferSubData(ssbo_id_, 0, size_in_bytes_, data);
+  }
+  else {
+    /* This binds the buffer to GL_ARRAY_BUFFER and upload the data if any. */
+    glBindBuffer(GL_SHADER_STORAGE_BUFFER, ssbo_id_);
+    glGetBufferSubData(GL_SHADER_STORAGE_BUFFER, 0, size_in_bytes_, data);
+    glBindBuffer(GL_SHADER_STORAGE_BUFFER, 0);
+  }
+}
+
 /** \} */
 
 }  // namespace blender::gpu
diff --git a/source/blender/gpu/opengl/gl_storage_buffer.hh b/source/blender/gpu/opengl/gl_storage_buffer.hh
index ffe2de12451..680ce911bc7 100644
--- a/source/blender/gpu/opengl/gl_storage_buffer.hh
+++ b/source/blender/gpu/opengl/gl_storage_buffer.hh
@@ -35,6 +35,7 @@ class GLStorageBuf : public StorageBuf {
   void unbind() override;
   void clear(eGPUTextureFormat internal_format, eGPUDataFormat data_format, void *data) override;
   void copy_sub(VertBuf *src, uint dst_offset, uint src_offset, uint copy_size) override;
+  void read(void *data) override;
 
   /* Special internal function to bind SSBOs to indirect argument targets. */
   void bind_as(GLenum target);