gl::query class, use of occlusion queries in glare rendering

gl/buffer.cpp

@@ -3,7 +3,7 @@
 
 GLenum gl::buffer::glenum_target(gl::buffer::targets target)
 {
-    GLenum mapping[13] =
+	static GLenum mapping[13] =
     {
         GL_ARRAY_BUFFER,
         GL_ATOMIC_COUNTER_BUFFER,

gl/query.cpp

@@ -0,0 +1,60 @@
+#include "stdafx.h"
+#include "query.h"
+
+gl::query::query(targets target)
+    : target(target)
+{
+	glGenQueries(1, *this);
+}
+
+gl::query::~query()
+{
+	end();
+	glDeleteQueries(1, *this);
+}
+
+void gl::query::begin()
+{
+	if (active_queries[target])
+		active_queries[target]->end();
+
+	glBeginQuery(glenum_target(target), *this);
+	active_queries[target] = this;
+}
+
+void gl::query::end()
+{
+	if (active_queries[target] != this)
+		return;
+
+	glEndQuery(glenum_target(target));
+	active_queries[target] = nullptr;
+}
+
+std::optional<int64_t> gl::query::result()
+{
+	GLuint ready;
+	glGetQueryObjectuiv(*this, GL_QUERY_RESULT_AVAILABLE, &ready);
+	int64_t value;
+	if (ready) {
+		glGetQueryObjecti64v(*this, GL_QUERY_RESULT, &value);
+		return std::optional<int64_t>(value);
+	}
+	return std::nullopt;
+}
+
+GLenum gl::query::glenum_target(targets target)
+{
+	static GLenum mapping[6] =
+	{
+	    GL_SAMPLES_PASSED,
+	    GL_ANY_SAMPLES_PASSED,
+	    GL_ANY_SAMPLES_PASSED_CONSERVATIVE,
+	    GL_PRIMITIVES_GENERATED,
+	    GL_TRANSFORM_FEEDBACK_PRIMITIVES_WRITTEN,
+	    GL_TIME_ELAPSED
+	};
+	return mapping[target];
+}
+
+thread_local gl::query* gl::query::active_queries[6];

gl/query.h

@@ -0,0 +1,36 @@
+#pragma once
+
+#include "object.h"
+
+namespace gl
+{
+class query : public object
+{
+public:
+	enum targets
+	{
+		SAMPLES_PASSED = 0,
+		ANY_SAMPLES_PASSED,
+		ANY_SAMPLES_PASSED_CONSERVATIVE,
+		PRIMITIVES_GENERATED,
+		TRANSFORM_FEEDBACK_PRIMITIVES_WRITTEN,
+		TIME_ELAPSED
+	};
+
+private:
+	targets target;
+	thread_local static query* active_queries[6];
+
+protected:
+	GLenum glenum_target(targets target);
+
+public:
+	query(targets target);
+	~query();
+
+	void begin();
+	void end();
+
+	std::optional<int64_t> result();
+};
+}