Overallocate dynamic buffers on resize.

src/bgfx_p.h

@@ -3398,7 +3398,7 @@ namespace bgfx
 					return NonLocalAllocator::kInvalidBlock;
 				}
 
-				const uint32_t allocSize = bx::max<uint32_t>(BGFX_CONFIG_DYNAMIC_INDEX_BUFFER_SIZE, _size);
+				const uint32_t allocSize = bx::max<uint32_t>(BGFX_CONFIG_DYNAMIC_INDEX_BUFFER_SIZE, bx::alignUp(_size, 1<<20) );
 
 				IndexBuffer& ib = m_indexBuffers[indexBufferHandle.idx];
 				ib.m_size = allocSize;
@@ -3582,7 +3582,7 @@ namespace bgfx
 					return NonLocalAllocator::kInvalidBlock;
 				}
 
-				const uint32_t allocSize = bx::max<uint32_t>(BGFX_CONFIG_DYNAMIC_VERTEX_BUFFER_SIZE, _size);
+				const uint32_t allocSize = bx::max<uint32_t>(BGFX_CONFIG_DYNAMIC_VERTEX_BUFFER_SIZE, bx::alignUp(_size, 1<<20) );
 
 				VertexBuffer& vb = m_vertexBuffers[vertexBufferHandle.idx];
 				vb.m_size   = allocSize;