From d15bb0c4fa9a89576d8cacc544e713346535555f Mon Sep 17 00:00:00 2001
From: nmlgc <nmlgc@nmlgc.net>
Date: Sun, 26 Feb 2023 20:00:18 +0100
Subject: [PATCH] [Platform] [PC-98] Graphics GDC initialization

I've copy-pasted this snippet so many times, it's time it gets a proper
home.

Part of P0232, funded by [Anonymous].
---
 platform/x86real/pc98/graph.cpp | 18 ++++++++++++++++++
 platform/x86real/pc98/graph.hpp |  5 +++++
 2 files changed, 23 insertions(+)
 create mode 100644 platform/x86real/pc98/graph.cpp
 create mode 100644 platform/x86real/pc98/graph.hpp

diff --git a/platform/x86real/pc98/graph.cpp b/platform/x86real/pc98/graph.cpp
new file mode 100644
index 00000000..c56589c9
--- /dev/null
+++ b/platform/x86real/pc98/graph.cpp
@@ -0,0 +1,18 @@
+#include "platform.h"
+#include "x86real.h"
+#include "platform/x86real/pc98/graph.hpp"
+
+void graph_show_16color_400line(void)
+{
+	// Enter 400-line mode
+	_AH = 0x42;
+	_CH = 0xC0;
+	geninterrupt(0x18);
+
+	// Enter 16-color mode
+	outportb(0x6A, 1);
+
+	// Show VRAM
+	_AH = 0x40;
+	geninterrupt(0x18);
+}
diff --git a/platform/x86real/pc98/graph.hpp b/platform/x86real/pc98/graph.hpp
new file mode 100644
index 00000000..600afb8f
--- /dev/null
+++ b/platform/x86real/pc98/graph.hpp
@@ -0,0 +1,5 @@
+// Generic graphics layer functions
+// --------------------------------
+
+// Puts the graphics GDC into the common 16-color 640×400 graphics mode.
+void graph_show_16color_400line(void);