From aee648bfa5e94e12a9dd8478fc45c4e8db0bb1f9 Mon Sep 17 00:00:00 2001
From: Adam Macdonald <72780006+twokilohertz@users.noreply.github.com>
Date: Wed, 5 Mar 2025 18:44:12 +0000
Subject: [PATCH] Add framebuffer to prevent redraw flicker

---
 Cargo.lock          | 20 ++++++++++++++++++++
 Cargo.toml          |  5 ++++-
 src/display_task.rs | 27 +++++++++++++++++++--------
 3 files changed, 43 insertions(+), 9 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index aae1f1a..bc07f82 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -424,6 +424,15 @@ version = "0.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "4fc247028eae04174b6635104a35b1ed336aabef4654f5e87a8f32327d231970"
 
+[[package]]
+name = "embedded-dma"
+version = "0.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "994f7e5b5cb23521c22304927195f236813053eb9c065dd2226a32ba64695446"
+dependencies = [
+ "stable_deref_trait",
+]
+
 [[package]]
 name = "embedded-graphics"
 version = "0.8.1"
@@ -447,6 +456,16 @@ dependencies = [
  "byteorder",
 ]
 
+[[package]]
+name = "embedded-graphics-framebuf"
+version = "0.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "22354420f68727fa24d1e2741dae1e9a041065e80fb63b35a8d19c647a85be76"
+dependencies = [
+ "embedded-dma",
+ "embedded-graphics",
+]
+
 [[package]]
 name = "embedded-hal"
 version = "0.2.7"
@@ -869,6 +888,7 @@ dependencies = [
  "embassy-sync",
  "embassy-time",
  "embedded-graphics",
+ "embedded-graphics-framebuf",
  "heapless",
  "rtt-target",
  "scd4x",
diff --git a/Cargo.toml b/Cargo.toml
index 695e6ad..dd6fd6f 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -25,12 +25,15 @@ embassy-time = "0.4.0"
 embassy-sync = "0.6.2"
 embassy-embedded-hal = "0.3.0"
 static_cell = "2.1.0"
-embedded-graphics = "0.8.1"
 
 # System
 cortex-m-rt = "0.7.5"
 rtt-target = "0.6.1"
 
+# embedded-graphics
+embedded-graphics = "0.8.1"
+embedded-graphics-framebuf = "0.5.0"
+
 # Peripherals
 scd4x = { git = "https://github.com/twokilohertz/scd4x-rs.git", branch = "conversion-fixes", features = [
     "scd41",
diff --git a/src/display_task.rs b/src/display_task.rs
index 1dcdba0..440bb9a 100644
--- a/src/display_task.rs
+++ b/src/display_task.rs
@@ -1,6 +1,7 @@
 // System
 use embassy_embedded_hal::shared_bus::blocking::spi::SpiDeviceWithConfig;
 use embassy_rp::{gpio::Output, spi::Config};
+use embedded_graphics_framebuf::FrameBuf;
 use rtt_target::rprintln;
 
 // Display
@@ -13,9 +14,11 @@ use ssd1351::{
 
 // Graphics
 use embedded_graphics::{
+    draw_target::DrawTarget,
     mono_font::{ascii::FONT_6X10, MonoTextStyle},
     pixelcolor::Rgb565,
-    prelude::{Point, WebColors},
+    prelude::{Point, RgbColor, Size, WebColors},
+    primitives::Rectangle,
     text::{Alignment, Text},
     Drawable,
 };
@@ -46,6 +49,10 @@ pub async fn display_output_task(
     display.reset(rst, &mut embassy_time::Delay).unwrap();
     display.init().unwrap();
 
+    // Framebuffer, prevents flickering on redraw
+    let buf = [Rgb565::BLACK; 128 * 128];
+    let mut framebuf = FrameBuf::new(buf, 128, 128);
+
     let co2_text_style = MonoTextStyle::new(&FONT_6X10, Rgb565::CSS_DARK_GREEN);
     let temp_text_style = MonoTextStyle::new(&FONT_6X10, Rgb565::CSS_ORANGE);
     let humidity_text_style = MonoTextStyle::new(&FONT_6X10, Rgb565::CSS_AQUA);
@@ -55,7 +62,10 @@ pub async fn display_output_task(
     let mut humidity_text_buf = heapless::String::<16>::new();
 
     loop {
-        // Clear contents of buffers
+        // Clear the framebuffer
+        framebuf.clear(Rgb565::BLACK).unwrap();
+
+        // Clear contents of text buffers
         co2_text_buf.clear();
         temp_text_buf.clear();
         humidity_text_buf.clear();
@@ -66,9 +76,6 @@ pub async fn display_output_task(
         write!(&mut temp_text_buf, "Temp: {:.1} C", data.temperature).unwrap();
         write!(&mut humidity_text_buf, "RH: {:.1} %", data.humidity).unwrap();
 
-        // Clear the display
-        display.clear();
-
         // Draw the text to the screen
         Text::with_alignment(
             &co2_text_buf,
@@ -76,7 +83,7 @@ pub async fn display_output_task(
             co2_text_style,
             Alignment::Left,
         )
-        .draw(&mut display)
+        .draw(&mut framebuf)
         .unwrap();
 
         Text::with_alignment(
@@ -85,7 +92,7 @@ pub async fn display_output_task(
             temp_text_style,
             Alignment::Left,
         )
-        .draw(&mut display)
+        .draw(&mut framebuf)
         .unwrap();
 
         Text::with_alignment(
@@ -94,7 +101,11 @@ pub async fn display_output_task(
             humidity_text_style,
             Alignment::Left,
         )
-        .draw(&mut display)
+        .draw(&mut framebuf)
         .unwrap();
+
+        // Draw the entire framebuffer to the display
+        let area: Rectangle = Rectangle::new(Point::new(0, 0), Size::new(128, 128));
+        display.fill_contiguous(&area, framebuf.data).unwrap();
     }
 }