Add glContainer::at override to update a single item

2 files changed, 39 insertions, 0 deletions

diff --git a/lib/glContainer.h b/lib/glContainer.h
index e5f53e2..ce88916 100644
--- a/lib/glContainer.h
+++ b/lib/glContainer.h
@@ -136,6 +136,22 @@ public:
 		return size_;
 	}
 
+	void
+	at(size_type pos, const T & value)
+	{
+		if (pos >= size()) {
+			throw std::out_of_range {__FUNCTION__};
+		}
+		if (data_.data()) {
+			data_[pos] = value;
+		}
+		else {
+			glBindBuffer(GL_ARRAY_BUFFER, buffer_);
+			glBufferSubData(GL_ARRAY_BUFFER, static_cast<GLintptr>(pos * sizeof(T)), sizeof(value), &value);
+			glBindBuffer(GL_ARRAY_BUFFER, 0);
+		}
+	}
+
 	[[nodiscard]] reference_type
 	at(size_type pos)
 	{
diff --git a/test/test-glContainer.cpp b/test/test-glContainer.cpp
index 9d4f198..0597470 100644
--- a/test/test-glContainer.cpp
+++ b/test/test-glContainer.cpp
@@ -204,6 +204,29 @@ BOOST_AUTO_TEST_CASE(random_access)
 	BOOST_CHECK_EQUAL(1, *i);
 }
 
+BOOST_AUTO_TEST_CASE(random_write)
+{
+	BOOST_CHECK_NO_THROW(resize(3));
+	BOOST_CHECK_EQUAL(size(), 3);
+	BOOST_CHECK_NO_THROW(unmap());
+	BOOST_REQUIRE(!data_.data());
+	BOOST_CHECK_NO_THROW(at(0, 10));
+	BOOST_CHECK_NO_THROW(at(1, 20));
+	BOOST_CHECK_NO_THROW(at(2, 30));
+	BOOST_CHECK(!data_.data());
+	{
+		std::array expected1 {10, 20, 30};
+		BOOST_CHECK_EQUAL_COLLECTIONS(begin(), end(), expected1.begin(), expected1.end());
+	}
+	BOOST_CHECK(data_.data());
+	BOOST_CHECK_NO_THROW(at(1, 40));
+	{
+		std::array expected1 {10, 40, 30};
+		BOOST_CHECK_EQUAL_COLLECTIONS(begin(), end(), expected1.begin(), expected1.end());
+	}
+	BOOST_CHECK_THROW(at(4, 0), std::out_of_range);
+}
+
 BOOST_AUTO_TEST_CASE(insert_remove_test)
 {
 	BOOST_CHECK_NO_THROW(emplace_back(1));