From 6080120777fdf7b6e1184288eff9d205ca7ebf5f Mon Sep 17 00:00:00 2001
From: Mikko Rasa <tdb@tdb.fi>
Date: Wed, 17 Nov 2021 14:48:58 +0200
Subject: [PATCH] Add a usage parameter to Buffer

It has no real meaning on OpenGL but is needed on Vulkan
---
 source/backends/opengl/texture2d_backend.cpp |  2 +-
 source/core/buffer.cpp                       |  3 ++-
 source/core/buffer.h                         | 19 ++++++++++++++++---
 source/core/mesh.cpp                         |  4 ++--
 source/render/instancearray.cpp              |  2 +-
 source/render/programdata.cpp                |  2 +-
 6 files changed, 23 insertions(+), 9 deletions(-)

diff --git a/source/backends/opengl/texture2d_backend.cpp b/source/backends/opengl/texture2d_backend.cpp
index 2f396df4..45ba78cc 100644
--- a/source/backends/opengl/texture2d_backend.cpp
+++ b/source/backends/opengl/texture2d_backend.cpp
@@ -167,7 +167,7 @@ bool OpenGLTexture2D::AsyncLoader::process()
 	}
 	else if(phase==1)
 	{
-		pixel_buffer.storage(n_bytes);
+		pixel_buffer.storage(n_bytes, STREAMING);
 		mapped_address = reinterpret_cast<char *>(pixel_buffer.map());
 	}
 	else if(phase==2)
diff --git a/source/core/buffer.cpp b/source/core/buffer.cpp
index 240fcd72..15a37397 100644
--- a/source/core/buffer.cpp
+++ b/source/core/buffer.cpp
@@ -8,7 +8,7 @@ using namespace std;
 namespace Msp {
 namespace GL {
 
-void Buffer::storage(size_t sz)
+void Buffer::storage(size_t sz, BufferUsage u)
 {
 	if(size>0)
 	{
@@ -20,6 +20,7 @@ void Buffer::storage(size_t sz)
 		throw invalid_argument("Buffer::storage");
 
 	size = sz;
+	usage = u;
 
 	allocate();
 }
diff --git a/source/core/buffer.h b/source/core/buffer.h
index b642738e..a12b3373 100644
--- a/source/core/buffer.h
+++ b/source/core/buffer.h
@@ -15,6 +15,12 @@ public:
 	virtual ~buffer_too_small() throw() { }
 };
 
+enum BufferUsage
+{
+	STATIC,
+	STREAMING
+};
+
 /**
 Stores data in GPU memory.
 
@@ -22,6 +28,10 @@ Memory must be allocated for the buffer by calling storage().  Contents can
 then be modified either synchronously with the data() and sub_data() functions,
 or asynchronously by memory-mapping the buffer.
 
+Buffers can have a static or streaming usage pattern.  Streaming buffers can be
+memory mapped for less update overhead, but memory space is more limited.  If
+the buffer is updated only rarely, static is recommended.
+
 Applications normally don't need to deal with Buffers directly.  They're
 managed by other classes such as Mesh and ProgramData.
 */
@@ -31,11 +41,13 @@ class Buffer: public BufferBackend
 
 private:
 	std::size_t size = 0;
+	BufferUsage usage = STATIC;
+	bool mapped = false;
 
 public:
-	/** Sets the storage size and allocates memory for the buffer.  Size cannot
-	be changed once set. */
-	void storage(std::size_t);
+	/** Sets storage size and usage pattern and allocates memory for the buffer.
+	Size and usage cannot be changed once set. */
+	void storage(std::size_t, BufferUsage);
 
 	/** Replaces contents of the entire buffer.  Allocated storage must exist.
 	The data must have size matching the defined storage. */
@@ -46,6 +58,7 @@ public:
 	void sub_data(std::size_t, std::size_t, const void *);
 
 	std::size_t get_size() const { return size; }
+	BufferUsage get_usage() const { return usage; }
 
 	void require_size(std::size_t) const;
 
diff --git a/source/core/mesh.cpp b/source/core/mesh.cpp
index 208126ef..360d588f 100644
--- a/source/core/mesh.cpp
+++ b/source/core/mesh.cpp
@@ -211,9 +211,9 @@ void Mesh::draw(Renderer &renderer, const VertexSetup *vs, unsigned count) const
 void Mesh::resize_buffers() const
 {
 	if(dirty&VERTEX_BUFFER)
-		vbuf->storage(vertices.get_required_buffer_size());
+		vbuf->storage(vertices.get_required_buffer_size(), STATIC);
 	if((dirty&INDEX_BUFFER) && !batches.empty())
-		ibuf->storage(batches.front().get_required_buffer_size());
+		ibuf->storage(batches.front().get_required_buffer_size(), STATIC);
 	dirty = 0;
 }
 
diff --git a/source/render/instancearray.cpp b/source/render/instancearray.cpp
index 4a24ac45..eec72f98 100644
--- a/source/render/instancearray.cpp
+++ b/source/render/instancearray.cpp
@@ -105,7 +105,7 @@ void InstanceArray::render(Renderer &renderer, Tag tag) const
 	const Mesh *mesh = object.get_mesh();
 	mesh->get_vertices().refresh();
 	if(instance_buffer->get_size()==0)
-		instance_buffer->storage(instance_data.get_required_buffer_size());
+		instance_buffer->storage(instance_data.get_required_buffer_size(), STREAMING);
 	instance_data.refresh();
 
 	Renderer::Push push(renderer);
diff --git a/source/render/programdata.cpp b/source/render/programdata.cpp
index a908284b..fc9b30a9 100644
--- a/source/render/programdata.cpp
+++ b/source/render/programdata.cpp
@@ -656,7 +656,7 @@ vector<ProgramData::ProgramBlock>::const_iterator ProgramData::prepare_program(c
 #endif
 				}
 
-				buffer->storage(required_size);
+				buffer->storage(required_size, STREAMING);
 			}
 		}
 	}
-- 
2.45.2