Add SSBO and compute shader support to gl wrappers

gl/ssbo.h

@@ -0,0 +1,47 @@
+#pragma once
+
+#include <type_traits>
+
+#include "object.h"
+
+namespace gl
+{
+	// shader storage buffer (std430 data, compute shader input and output), on 4.6 core direct state access.
+	// the storage is immutable: resize() to a different size replaces the buffer object, drops its contents and
+	// leaves it unbound (call bind_base() again).
+	// binding goes through glBindBuffersBase, which leaves the general GL_SHADER_STORAGE_BUFFER binding point
+	// alone, so the binding tracker of gl::buffer stays valid
+	class ssbo : public object
+	{
+	  public:
+		// size in bytes, > 0. index is the binding point used by the shaders: layout(std430, binding = index)
+		ssbo(GLsizeiptr size, GLuint index);
+		~ssbo();
+
+		void bind_base() const;
+		void resize(GLsizeiptr size);
+		GLsizeiptr size() const
+		{
+			return m_size;
+		}
+
+		void update(const void *data, GLintptr offset, GLsizeiptr size);
+		template <typename T> void update(const T &data, GLintptr offset = 0)
+		{
+			static_assert(std::is_trivially_copyable_v<T>, "ssbo data must be trivially copyable");
+			update(&data, offset, sizeof(data));
+		}
+		// synchronous read back, waits for the gpu; for debug data, not for per-frame use
+		void download(void *data, GLintptr offset, GLsizeiptr size) const;
+
+	  private:
+		void create(GLsizeiptr size);
+
+		GLuint m_index;
+		GLsizeiptr m_size = 0;
+	};
+
+	// makes writes done by shaders (compute dispatches, storage buffer stores) visible to the operations named
+	// by barriers, e.g. GL_SHADER_STORAGE_BARRIER_BIT before a draw that reads what a dispatch wrote
+	void memory_barrier(GLbitfield barriers);
+} // namespace gl