From ad3fa0b214e73be4655e8ebedfff63208a80aab6 Mon Sep 17 00:00:00 2001
From: Dan Goodliffe <dan@randomdan.homeip.net>
Date: Tue, 25 Feb 2025 00:08:13 +0000
Subject: Add glMappedBufferWriter helper

Usable as an out iterator to transform directly to GPU mapped memory
---
 lib/glMappedBufferWriter.h | 78 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 78 insertions(+)
 create mode 100644 lib/glMappedBufferWriter.h

(limited to 'lib/glMappedBufferWriter.h')

diff --git a/lib/glMappedBufferWriter.h b/lib/glMappedBufferWriter.h
new file mode 100644
index 0000000..f97d7e1
--- /dev/null
+++ b/lib/glMappedBufferWriter.h
@@ -0,0 +1,78 @@
+#pragma once
+
+#include "special_members.h"
+#include <cstddef>
+#include <glad/gl.h>
+#include <utility>
+
+template<typename T> class glMappedBufferWriter {
+public:
+	using difference_type = std::ptrdiff_t;
+
+	glMappedBufferWriter(GLenum target, GLuint buffer, size_t count, GLenum usage = GL_STATIC_DRAW) :
+		target {target}, data {[&]() {
+			glBindBuffer(target, buffer);
+			glBufferData(target, static_cast<GLsizeiptr>(sizeof(T) * count), nullptr, usage);
+			return static_cast<T *>(glMapBuffer(target, GL_WRITE_ONLY));
+		}()}
+	{
+	}
+
+	~glMappedBufferWriter()
+	{
+		if (target) {
+			glUnmapBuffer(target);
+		}
+	}
+
+	glMappedBufferWriter(glMappedBufferWriter && other) noexcept :
+		target {std::exchange(other.target, 0)}, data {std::exchange(other.data, nullptr)}
+	{
+	}
+
+	glMappedBufferWriter &
+	operator=(glMappedBufferWriter && other) noexcept
+	{
+		if (target) {
+			glUnmapBuffer(target);
+		}
+		target = std::exchange(other.target, 0);
+		data = std::exchange(other.data, nullptr);
+		return *this;
+	}
+
+	NO_COPY(glMappedBufferWriter);
+
+	glMappedBufferWriter &
+	operator++()
+	{
+		data++;
+		return *this;
+	}
+
+	glMappedBufferWriter &
+	operator++(int)
+	{
+		glMappedBufferWriter rtn {data};
+		data++;
+		return rtn;
+	}
+
+	T &
+	operator*()
+	{
+		return *data;
+	}
+
+	T *
+	operator->() const
+	{
+		return data;
+	}
+
+private:
+	explicit glMappedBufferWriter(T * data) : target {0}, data {data} { }
+
+	GLenum target;
+	T * data;
+};
-- 
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