Add support for 72x40px SSD1306 modules (#101)

* Add 72x40 display size

* Add copypasta 72x40 demo

* Set COM pin config correctly

The display I have at least uses an alternate row connection mapping as
opposed to sequential. Without this change, the display skips every
second row and makes everything stretched 2x in Y

* Add support for display offsets

Adds offset of (28, 0) as discovered by this Reddit post:

https://www.reddit.com/r/arduino/comments/bup1kf/anyone_got_one_of_these_little_beauties_working/

* Refactor 70x42 example for centered layout

* Add changelog entry

* Fix example

* Update 70x42 example for e-g 0.6.0-alpha.3

CHANGELOG.md

@@ -6,6 +6,10 @@
 
 ## [Unreleased] - ReleaseDate
 
+### Added
+
+- [#101](https://github.com/jamwaffles/ssd1306/pull/101) Add support for modules with a 72x40px display size. These are often advertised as 70x40px displays which are likely the same hardware. An example is also added - `graphics_i2c_72x40`.
+
 ### Fixed
 
 - Fix docs.rs build by targeting `x86_64-unknown-linux-gnu`

examples/graphics_i2c_72x40.rs

@@ -0,0 +1,130 @@
+//! Draw a square, circle and triangle on the screen using the `embedded_graphics` crate.
+//!
+//! This example is for the STM32F103 "Blue Pill" board using I2C1.
+//!
+//! Wiring connections are as follows for a CRIUS-branded display:
+//!
+//! ```
+//!      Display -> Blue Pill
+//! (black)  GND -> GND
+//! (red)    +5V -> VCC
+//! (yellow) SDA -> PB9
+//! (green)  SCL -> PB8
+//! ```
+//!
+//! Run on a Blue Pill with `cargo run --example graphics_i2c`.
+
+#![no_std]
+#![no_main]
+
+extern crate cortex_m;
+extern crate cortex_m_rt as rt;
+extern crate panic_semihosting;
+extern crate stm32f1xx_hal as hal;
+
+use cortex_m_rt::{entry, exception, ExceptionFrame};
+use embedded_graphics::{
+    pixelcolor::BinaryColor,
+    prelude::*,
+    primitives::{Circle, Rectangle, Triangle},
+    style::PrimitiveStyleBuilder,
+};
+use hal::{
+    i2c::{BlockingI2c, DutyCycle, Mode},
+    prelude::*,
+    stm32,
+};
+use ssd1306::{prelude::*, Builder};
+
+#[entry]
+fn main() -> ! {
+    let dp = stm32::Peripherals::take().unwrap();
+
+    let mut flash = dp.FLASH.constrain();
+    let mut rcc = dp.RCC.constrain();
+
+    let clocks = rcc.cfgr.freeze(&mut flash.acr);
+
+    let mut afio = dp.AFIO.constrain(&mut rcc.apb2);
+
+    let mut gpiob = dp.GPIOB.split(&mut rcc.apb2);
+
+    let scl = gpiob.pb8.into_alternate_open_drain(&mut gpiob.crh);
+    let sda = gpiob.pb9.into_alternate_open_drain(&mut gpiob.crh);
+
+    let i2c = BlockingI2c::i2c1(
+        dp.I2C1,
+        (scl, sda),
+        &mut afio.mapr,
+        Mode::Fast {
+            frequency: 400_000.hz(),
+            duty_cycle: DutyCycle::Ratio2to1,
+        },
+        clocks,
+        &mut rcc.apb1,
+        1000,
+        10,
+        1000,
+        1000,
+    );
+
+    let mut disp: GraphicsMode<_> = Builder::new()
+        .size(DisplaySize::Display72x40)
+        .connect_i2c(i2c)
+        .into();
+
+    disp.init().unwrap();
+
+    let size = 10;
+    let offset = Point::new(10, (42 / 2) - (size / 2) - 1);
+    let spacing = size + 10;
+
+    let style = PrimitiveStyleBuilder::new()
+        .stroke_width(1)
+        .stroke_color(BinaryColor::On)
+        .build();
+
+    // screen outline
+    // default display size is 128x64 if you don't pass a _DisplaySize_
+    // enum to the _Builder_ struct
+    Rectangle::new(Point::new(0, 0), Point::new(71, 39))
+        .into_styled(style)
+        .draw(&mut disp);
+
+    // Triangle
+    Triangle::new(
+        Point::new(0, size),
+        Point::new(size / 2, 0),
+        Point::new(size, size),
+    )
+    .translate(offset)
+    .into_styled(style)
+    .draw(&mut disp);
+
+    // Move over to next position
+    let offset = offset + Point::new(spacing, 0);
+
+    // Draw a square
+    Rectangle::new(Point::new(0, 0), Point::new(size, size))
+        .translate(offset)
+        .into_styled(style)
+        .draw(&mut disp);
+
+    // Move over a bit more
+    let offset = offset + Point::new(spacing, 0);
+
+    // Circle
+    Circle::new(Point::new(size / 2, size / 2), size as u32 / 2)
+        .translate(offset)
+        .into_styled(style)
+        .draw(&mut disp);
+
+    disp.flush().unwrap();
+
+    loop {}
+}
+
+#[exception]
+fn HardFault(ef: &ExceptionFrame) -> ! {
+    panic!("{:#?}", ef);
+}

src/displaysize.rs

@@ -10,6 +10,8 @@ pub enum DisplaySize {
     Display128x32,
     /// 96 by 16 pixels
     Display96x16,
+    /// 70 by 42 pixels
+    Display72x40,
 }
 
 impl DisplaySize {
@@ -20,6 +22,7 @@ impl DisplaySize {
             DisplaySize::Display128x64 => (128, 64),
             DisplaySize::Display128x32 => (128, 32),
             DisplaySize::Display96x16 => (96, 16),
+            DisplaySize::Display72x40 => (72, 40),
         }
     }
 }

src/mode/graphics.rs

@@ -159,11 +159,17 @@ where
         self.min_y = width - 1;
         self.max_y = 0;
 
+        // Compensate for any offset in the physical display. For example, the 72x40 display has an
+        // offset of (28, 0) pixels.
+        let offs = self.properties.display_offset;
+
         // Tell the display to update only the part that has changed
         match self.properties.get_rotation() {
             DisplayRotation::Rotate0 | DisplayRotation::Rotate180 => {
-                self.properties
-                    .set_draw_area((disp_min_x, disp_min_y), (disp_max_x, disp_max_y))?;
+                self.properties.set_draw_area(
+                    (disp_min_x + offs.0, disp_min_y + offs.1),
+                    (disp_max_x + offs.0, disp_max_y + offs.1),
+                )?;
 
                 self.properties.bounded_draw(
                     &self.buffer,
@@ -173,8 +179,10 @@ where
                 )
             }
             DisplayRotation::Rotate90 | DisplayRotation::Rotate270 => {
-                self.properties
-                    .set_draw_area((disp_min_y, disp_min_x), (disp_max_y, disp_max_x))?;
+                self.properties.set_draw_area(
+                    (disp_min_y + offs.1, disp_min_x + offs.0),
+                    (disp_max_y + offs.1, disp_max_x + offs.0),
+                )?;
 
                 self.properties.bounded_draw(
                     &self.buffer,

src/mode/terminal.rs

@@ -176,10 +176,13 @@ where
     pub fn clear(&mut self) -> Result<(), TerminalModeError<DI>> {
         let display_size = self.properties.get_size();
 
+        // The number of characters that can fit on the display at once (w * h / 8 * 8)
+        // TODO: Use `display_size.dimensions()`
         let numchars = match display_size {
             DisplaySize::Display128x64 => 128,
             DisplaySize::Display128x32 => 64,
             DisplaySize::Display96x16 => 24,
+            DisplaySize::Display72x40 => 45,
         };
 
         // Let the chip handle line wrapping so we can fill the screen with blanks faster
@@ -191,6 +194,7 @@ where
             .set_draw_area((0, 0), (display_width, display_height))
             .terminal_err()?;
 
+        // Clear the display
         for _ in 0..numchars {
             self.properties.draw(&[0; 8]).terminal_err()?;
         }

src/properties.rs

@@ -12,6 +12,7 @@ pub struct DisplayProperties<DI> {
     iface: DI,
     display_size: DisplaySize,
     display_rotation: DisplayRotation,
+    pub(crate) display_offset: (u8, u8),
     addr_mode: AddrMode,
 }
 
@@ -25,10 +26,18 @@ where
         display_size: DisplaySize,
         display_rotation: DisplayRotation,
     ) -> DisplayProperties<DI> {
+        let display_offset = match display_size {
+            DisplaySize::Display128x64 => (0, 0),
+            DisplaySize::Display128x32 => (0, 0),
+            DisplaySize::Display96x16 => (0, 0),
+            DisplaySize::Display72x40 => (28, 0),
+        };
+
         DisplayProperties {
             iface,
             display_size,
             display_rotation,
+            display_offset,
             addr_mode: AddrMode::Page, // reset value
         }
     }
@@ -61,6 +70,7 @@ where
             DisplaySize::Display128x32 => Command::ComPinConfig(false, false).send(&mut self.iface),
             DisplaySize::Display128x64 => Command::ComPinConfig(true, false).send(&mut self.iface),
             DisplaySize::Display96x16 => Command::ComPinConfig(false, false).send(&mut self.iface),
+            DisplaySize::Display72x40 => Command::ComPinConfig(true, false).send(&mut self.iface),
         }?;
 
         Command::Contrast(0x8F).send(&mut self.iface)?;