From 8c0ad0007a08346018d679890be4d855a9b9e67f Mon Sep 17 00:00:00 2001
From: Jan-Henrik Bruhn <hi@jhbruhn.de>
Date: Thu, 19 Sep 2019 17:55:48 +0200
Subject: [PATCH] Implement double buffering for screen, only do transmission
 in interrupt handler

---
 midi2cv/drivers/display.cc | 22 ++++++++++++++++++++++
 midi2cv/drivers/display.h  | 16 +++++++++-------
 midi2cv/midi2cv.cc         |  4 ++--
 midi2cv/ui.cc              |  7 ++++++-
 midi2cv/ui.h               |  1 +
 5 files changed, 40 insertions(+), 10 deletions(-)

diff --git a/midi2cv/drivers/display.cc b/midi2cv/drivers/display.cc
index 43ed223..4bf80bb 100644
--- a/midi2cv/drivers/display.cc
+++ b/midi2cv/drivers/display.cc
@@ -12,6 +12,9 @@ const uint16_t kPinReset = GPIO_Pin_0;
 const uint16_t kPinDataCommand = GPIO_Pin_9;
 
 u8g2_t u8g2_;
+uint8_t* default_buf;
+uint8_t second_buf[1024];
+uint8_t* output_buf;
 
 u8g2_t* Display::u8g2()
 {
@@ -115,8 +118,27 @@ uint8_t u8x8_byte_4wire_hw_spi(u8x8_t* u8x8, uint8_t msg, uint8_t arg_int,
 void Display::InitGLib()
 {
     u8g2_Setup_sh1106_128x64_noname_f(&u8g2_, U8G2_R0, u8x8_byte_4wire_hw_spi, u8x8_stm32_gpio_and_delay);
+    output_buf = default_buf = u8g2_.tile_buf_ptr;
     u8g2_InitDisplay(&u8g2_);
     u8g2_SetContrast(&u8g2_, 127);
     u8g2_SetPowerSave(&u8g2_, 0);
+
     Random::Seed(42);
 }
+
+void Display::Flush()
+{
+    uint8_t* cache = u8g2_.tile_buf_ptr;
+    u8g2_.tile_buf_ptr = output_buf;
+    u8g2_SendBuffer(&u8g2_);
+    u8g2_.tile_buf_ptr = cache;
+}
+
+void Display::Swap()
+{
+    output_buf = u8g2_.tile_buf_ptr;
+    if (output_buf == default_buf)
+	u8g2_.tile_buf_ptr = second_buf;
+    else
+	u8g2_.tile_buf_ptr = default_buf;
+}
diff --git a/midi2cv/drivers/display.h b/midi2cv/drivers/display.h
index dfce649..9ecee24 100644
--- a/midi2cv/drivers/display.h
+++ b/midi2cv/drivers/display.h
@@ -1,21 +1,23 @@
 #ifndef MIDI2CV_DRIVERS_DISPLAY_H
 #define MIDI2CV_DRIVERS_DISPLAY_H
 
-#include <stm32f37x_conf.h>
 #include "stmlib/stmlib.h"
+#include <stm32f37x_conf.h>
 #include <u8g2.h>
 
-
 class Display {
-  public:
-    Display() { }
+public:
+    Display() {}
     ~Display() {}
 
     void Init();
-    u8g2_t* u8g2();    
-  private:
+    u8g2_t* u8g2();
+    void Flush();
+    void Swap();
+
+private:
     DISALLOW_COPY_AND_ASSIGN(Display);
-    void InitGLib();    
+    void InitGLib();
 };
 extern Display display;
 #endif
diff --git a/midi2cv/midi2cv.cc b/midi2cv/midi2cv.cc
index 7622ef9..df2ef34 100644
--- a/midi2cv/midi2cv.cc
+++ b/midi2cv/midi2cv.cc
@@ -60,7 +60,7 @@ void TIM2_IRQHandler(void)
     static uint8_t count = 0;
     count++;
     if (count % 192 == 0) {
-	ui.Update();
+	ui.Flush();
 	count = 0;
     }
 }
@@ -112,6 +112,6 @@ int main(void)
 {
     Init();
     while (1) {
-	//ui.Update();
+	ui.Update();
     }
 }
diff --git a/midi2cv/ui.cc b/midi2cv/ui.cc
index 78bb293..8643b15 100644
--- a/midi2cv/ui.cc
+++ b/midi2cv/ui.cc
@@ -27,5 +27,10 @@ void UI::Update()
 	dy = -1;
     if (y <= 7)
 	dy = 1;
-    u8g2_SendBuffer(u8g2_);
+    display.Swap();
+}
+
+void UI::Flush()
+{
+    display.Flush();
 }
diff --git a/midi2cv/ui.h b/midi2cv/ui.h
index dcb8bdd..351cd5d 100644
--- a/midi2cv/ui.h
+++ b/midi2cv/ui.h
@@ -9,6 +9,7 @@ public:
     ~UI() {}
 
     void Update();
+    void Flush();
 
 private:
     DISALLOW_COPY_AND_ASSIGN(UI);