GPU: Compute Pipeline.

With the compute pipeline calculation can be offloaded to the GPU.
This patch only adds the framework for compute. So no changes for users at
this moment.

NOTE: As this is an OpenGL4.3 feature it must always have a fallback.

Use `GPU_compute_shader_support` to check if compute pipeline can be used.
Check `gpu_shader_compute*` test cases for usage.

This patch also adds support for shader storage buffer objects and device only
vertex/index buffers.

An alternative that had been discussed was adding this to the `GPUBatch`, this
was eventually not chosen as it would lead to more code when used as part of a
shading group. The idea is that we add an `eDRWCommandType` in the near
future.

Reviewed By: fclem

Differential Revision: https://developer.blender.org/D10913

1 files changed, 28 insertions, 6 deletions

diff --git a/source/blender/gpu/opengl/gl_index_buffer.cc b/source/blender/gpu/opengl/gl_index_buffer.cc
index e2c18c5d0b9..e305f765ad9 100644
--- a/source/blender/gpu/opengl/gl_index_buffer.cc
+++ b/source/blender/gpu/opengl/gl_index_buffer.cc
@@ -40,17 +40,14 @@ void GLIndexBuf::bind()
     return;
   }
 
-  if (ibo_id_ == 0) {
+  const bool allocate_on_device = ibo_id_ == 0;
+  if (allocate_on_device) {
     glGenBuffers(1, &ibo_id_);
-
-    if (data_ == nullptr) {
-      debug::raise_gl_error("Trying to use Index Buffer but the buffer contains no data");
-    }
   }
 
   glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ibo_id_);
 
-  if (data_ != nullptr) {
+  if (data_ != nullptr || allocate_on_device) {
     size_t size = this->size_get();
     /* Sends data to GPU. */
     glBufferData(GL_ELEMENT_ARRAY_BUFFER, size, data_, GL_STATIC_DRAW);
@@ -59,4 +56,29 @@ void GLIndexBuf::bind()
   }
 }
 
+void GLIndexBuf::bind_as_ssbo(uint binding)
+{
+  bind();
+  BLI_assert(ibo_id_ != 0);
+  glBindBufferBase(GL_SHADER_STORAGE_BUFFER, binding, ibo_id_);
+}
+
+const uint32_t *GLIndexBuf::read() const
+{
+  BLI_assert(is_active());
+  void *data = glMapBuffer(GL_ELEMENT_ARRAY_BUFFER, GL_READ_ONLY);
+  uint32_t *result = static_cast<uint32_t *>(data);
+  return result;
+}
+
+bool GLIndexBuf::is_active() const
+{
+  if (!ibo_id_) {
+    return false;
+  }
+  int active_ibo_id = 0;
+  glGetIntegerv(GL_ELEMENT_ARRAY_BUFFER_BINDING, &active_ibo_id);
+  return ibo_id_ == active_ibo_id;
+}
+
 }  // namespace blender::gpu