GL: Added orphaning buffers to avoid transient buffer stalls. Issue #706.

src/renderer_gl.cpp

@@ -5383,13 +5383,13 @@ namespace bgfx { namespace gl
 		if (0 < _render->m_iboffset)
 		{
 			TransientIndexBuffer* ib = _render->m_transientIb;
-			m_indexBuffers[ib->handle.idx].update(0, _render->m_iboffset, ib->data);
+			m_indexBuffers[ib->handle.idx].update(0, _render->m_iboffset, ib->data, true);
 		}
 
 		if (0 < _render->m_vboffset)
 		{
 			TransientVertexBuffer* vb = _render->m_transientVb;
-			m_vertexBuffers[vb->handle.idx].update(0, _render->m_vboffset, vb->data);
+			m_vertexBuffers[vb->handle.idx].update(0, _render->m_vboffset, vb->data, true);
 		}
 
 		_render->sort();

src/renderer_gl.h

@@ -1058,9 +1058,17 @@ namespace bgfx { namespace gl
 			GL_CHECK(glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0) );
 		}
 
-		void update(uint32_t _offset, uint32_t _size, void* _data)
+		void update(uint32_t _offset, uint32_t _size, void* _data, bool _discard = false)
 		{
 			BX_CHECK(0 != m_id, "Updating invalid index buffer.");
+
+			if (_discard)
+			{
+				// orphan buffer...
+				destroy();
+				create(m_size, NULL, m_flags);
+			}
+
 			GL_CHECK(glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, m_id) );
 			GL_CHECK(glBufferSubData(GL_ELEMENT_ARRAY_BUFFER
 				, _offset
@@ -1104,9 +1112,17 @@ namespace bgfx { namespace gl
 			GL_CHECK(glBindBuffer(m_target, 0) );
 		}
 
-		void update(uint32_t _offset, uint32_t _size, void* _data)
+		void update(uint32_t _offset, uint32_t _size, void* _data, bool _discard = false)
 		{
 			BX_CHECK(0 != m_id, "Updating invalid vertex buffer.");
+
+			if (_discard)
+			{
+				// orphan buffer...
+				destroy();
+				create(m_size, NULL, m_decl, 0);
+			}
+
 			GL_CHECK(glBindBuffer(m_target, m_id) );
 			GL_CHECK(glBufferSubData(m_target
 				, _offset