Support Betaflight 4.5 four color fonts (avsaase#35)

* First cut on BF 4 page fonts

* Code formatting

* Fix clippy lint

* Refactor font type detection and font splitting

* Add unit tests

* Rename four page -> four color

* Update changelog

CHANGELOG.md

@@ -7,15 +7,19 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 ## [Unreleased]
 
 ### Added
+
 - Load last used OSD font file on startup (@dz0ny).
 - Option to render video with a chroma key background instead of the input video so the OSD can be overlayed in a video editor.
+- Support for Betaflight 4.5 four color fonts.
 
 ### Fixed
+
 - Bug that caused font files with unexpected number of characters to not open.
 
 ## [0.2.0] - 2023-04-23
 
 ### Added
+
 - Save OSD and SRT options between program runs.
 - Custom position and text size of SRT data.
 - Option to adjust OSD playback speed to correct for OSD lag with <=32.37.10 firmware.
@@ -24,56 +28,67 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 - Tooltips explaining options and settings.
 
 ### Changed
+
 - When loading a SRT file with distance data the distance checkbox doesn't get automatically checked.
 - Options sections can be collapsed to save screen space.
 
 ## [0.1.0] - 2023-03-31
 
 ### Fixed
+
 - Parsing of firmware version 32.37.10 SRT data.
 
 ## [0.1.0-beta4] - 2023-03-28
 
 ### Added
+
 - Render data from the SRT file on the video. Select which values are rendered.
 - Automatically load the matching OSD and SRT files when importing a video (they must be in the same folder and have the same file name).
 - Upscale output video to 1440p to get better compression on YouTube.
 
 ### Changed
+
 - New UI layout with better support for different screen sizes.
 - Many small UI tweaks.
 
 ### Fixed
+
 - Show correct number of characters in font file.
 
 ## [0.1.0-beta3] - 2023-03-21
 
 ### Added
+
 - Open files by dropping them on the window.
 - Improve render speed.
 - Logging of ffmpeg errors and warnings.
 - Option to select undetected encoders (use at your own risk).
 - Dark theme (default light, toggle by clicking the sun/moon icon in the top right).
 
 ### Changed
+
 - Improved handling of ffmpeg events.
 
 ### Fixed
+
 - Issue with non-critical ffmpeg errors stopping the render process.
 - Output videos not playable in some video players.
 
 ## [0.1.0-beta2] - 2023-03-15
 
 ### Added
+
 - Make main window resizable in vertical direction to accomodate retina displays and screens with lower resolutions.
 - Display errors from ffmpeg.
 - Display tooltip when hovering over start render button when it is disabled.
 
 ### Changed
+
 - Improved formatting of "About" window.
 - Improved display of render status when rendering is finished or cancelled.
 
 ### Fixed
+
 - Check for `hevc_videotoolbox` encoder on MacOS.
 - Stop ffmpeg decoder when encoder returns error.
 - Fixed version info display.
@@ -82,4 +97,5 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 ## [0.1.0-beta1] - 2023-03-11
 
 ### Added
+
 First beta release with limited features.

backend/Cargo.toml

@@ -18,3 +18,6 @@ serde = { version = "1.0.159", features = ["derive"] }
 srtparse = "0.2.0"
 thiserror = "1.0.38"
 tracing = "0.1.37"
+
+[dev-dependencies]
+claims = "0.7.1"

backend/src/ffmpeg/encoders.rs

@@ -1,8 +1,8 @@
+use std::{fmt::Display, path::PathBuf, process::Command};
+
 use rayon::prelude::*;
 use serde::{Deserialize, Serialize};
 
-use std::{fmt::Display, path::PathBuf, process::Command};
-
 #[derive(Debug, PartialEq, Clone, Serialize, Deserialize)]
 pub enum Codec {
     H264,

backend/src/ffmpeg/render.rs

@@ -11,15 +11,14 @@ use ffmpeg_sidecar::{
     event::{FfmpegEvent, LogLevel},
 };
 
+use super::{render_settings::RenderSettings, Encoder, FromFfmpegMessage, ToFfmpegMessage, VideoInfo};
 use crate::{
     font,
     osd::{self, OsdOptions},
     overlay::FrameOverlayIter,
     srt::{self, SrtOptions},
 };
 
-use super::{render_settings::RenderSettings, Encoder, FromFfmpegMessage, ToFfmpegMessage, VideoInfo};
-
 #[tracing::instrument(skip(osd_frames, srt_frames, font_file), err)]
 pub fn start_video_render(
     ffmpeg_path: &PathBuf,

backend/src/font/dimensions.rs

@@ -0,0 +1,109 @@
+use std::fmt::Display;
+
+use super::FontFileError;
+
+pub(crate) const CHARACTER_WIDTH_LARGE: u32 = 36;
+pub(crate) const CHARACTER_HEIGHT_LARGE: u32 = 54;
+pub(crate) const CHARACTER_WIDTH_SMALL: u32 = 24;
+pub(crate) const CHARACTER_HEIGHT_SMALL: u32 = 36;
+
+#[derive(Debug, Clone, PartialEq)]
+pub enum CharacterSize {
+    Large,
+    Small,
+}
+
+impl CharacterSize {
+    pub fn width(&self) -> u32 {
+        match self {
+            CharacterSize::Large => CHARACTER_WIDTH_LARGE,
+            CharacterSize::Small => CHARACTER_WIDTH_SMALL,
+        }
+    }
+
+    pub fn height(&self) -> u32 {
+        match self {
+            CharacterSize::Large => CHARACTER_HEIGHT_LARGE,
+            CharacterSize::Small => CHARACTER_HEIGHT_SMALL,
+        }
+    }
+}
+
+impl Display for CharacterSize {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(
+            f,
+            "{}",
+            match self {
+                CharacterSize::Large => "Large",
+                CharacterSize::Small => "Small",
+            }
+        )
+    }
+}
+
+#[derive(Debug, Clone, PartialEq)]
+pub enum FontType {
+    Standard,
+    FourColor,
+}
+
+impl FontType {
+    pub fn pages(&self) -> u32 {
+        match self {
+            FontType::Standard => 1,
+            FontType::FourColor => 4,
+        }
+    }
+}
+
+pub fn detect_dimensions(width: u32, height: u32) -> Result<(CharacterSize, FontType, u32), FontFileError> {
+    let (size, r#type) = if width == CHARACTER_WIDTH_SMALL {
+        (CharacterSize::Small, FontType::Standard)
+    } else if width == CHARACTER_WIDTH_LARGE {
+        (CharacterSize::Large, FontType::Standard)
+    } else if width == CHARACTER_WIDTH_SMALL * 4 {
+        (CharacterSize::Small, FontType::FourColor)
+    } else if width == CHARACTER_WIDTH_LARGE * 4 {
+        (CharacterSize::Large, FontType::FourColor)
+    } else {
+        return Err(FontFileError::InvalidFontFileWidth { width });
+    };
+
+    if height % size.height() != 0 {
+        return Err(FontFileError::InvalidFontFileHeight { height });
+    }
+
+    let characters_count = height / size.height();
+
+    Ok((size, r#type, characters_count))
+}
+
+#[cfg(test)]
+mod tests {
+    use claims::{assert_err, assert_ok_eq};
+
+    use super::*;
+
+    #[test]
+    fn detect_valid_font_sizes() {
+        let test_cases = [
+            (36, 13824, CharacterSize::Large, FontType::Standard, 256),
+            (24, 18432, CharacterSize::Small, FontType::Standard, 512),
+            (36, 27648, CharacterSize::Large, FontType::Standard, 512),
+            (96, 9216, CharacterSize::Small, FontType::FourColor, 256),
+            (144, 13824, CharacterSize::Large, FontType::FourColor, 256),
+        ];
+        for test in test_cases {
+            assert_ok_eq!(detect_dimensions(test.0, test.1), (test.2, test.3, test.4));
+        }
+    }
+
+    #[test]
+    fn reject_invalid_font_sizes() {
+        let test_cases = [(36, 13824 + 1), (24 + 1, 18432), (36 - 12, 27648 - 10)];
+        for test in test_cases {
+            assert_err!(detect_dimensions(test.0, test.1));
+        }
+    }
+}

backend/src/font/error.rs

@@ -21,4 +21,7 @@ pub enum FontFileError {
 
     #[error("Invalid fond file width {width}")]
     InvalidFontFileWidth { width: u32 },
+
+    #[error("Invalid fond file height {height}")]
+    InvalidFontFileHeight { height: u32 },
 }