Fix font atlas generation.

.gitignore

@@ -19,3 +19,6 @@ Cargo.lock
 #  and can be added to the global gitignore or merged into this file.  For a more nuclear
 #  option (not recommended) you can uncomment the following to ignore the entire idea folder.
 #.idea/
+
+
+font_atlas.png

Cargo.toml

@@ -8,8 +8,10 @@ sdl2 = { version = "0.37.0", default-features = false, features = ["gfx"] }
 itertools = "0.8.2"
 glium = "0.35.0"
 clap = { version="4.5.16", features=["derive"] }
-font-kit = "0.14.2"
+# font-kit = "0.14.2"
+font-kit = { path = "/home/leon/Projects/font-kit" }
 pathfinder_geometry = "0.5.1"
 log = "0.4.22"
 env_logger = "0.11.5"
 image = "0.25.2"
+freetype-sys = "0.20"

src/main.rs

@@ -89,7 +89,7 @@ fn gpu_mode() {
     println!("Initialized GPU context.");
 
     let font = load_default_fonts(); 
-    let font_atlas: font_kit::canvas::Canvas = generate_atlas(&font, 32.0);
+    let font_atlas: font_kit::canvas::Canvas = generate_atlas(&font, 32.0, None);
     let font_atlas_img = ImageBuffer::<Rgb<u8>, Vec<u8>>::from_raw(
         font_atlas.size.x() as u32, font_atlas.size.y() as u32, font_atlas.pixels
     ).unwrap();

src/text_rendering.rs

@@ -51,62 +51,70 @@ pub fn load_default_fonts() -> Font {
 }
 
 
-fn estimate_atlas_size(font: &Font, size: f32) -> (i32, i32){
+/// Estimates the size of a square atlas necessary to contain all the font letters.
+/// Padding is one-sided.
+fn estimate_atlas_size(font: &Font, size: f32, padding: i32) -> (i32, i32){
     let mut total_length = 0;
     let mut max_height = 0;
     for c in PrintableChars::new() {
         let glyph_id = font.glyph_for_char(c).expect(&format!("Could not lookup glyph for '{}' ({})", c, c as u32));
+        // This function is not accurate. A test shows that it may underpredict the raster bounds by up to 2 px.
         let raster_rect = font.raster_bounds(
             glyph_id, size,
             Transform2F::default(),
             HintingOptions::Vertical(size),
             RasterizationOptions::SubpixelAa
         ).unwrap();
-        total_length += raster_rect.width();
+        total_length += raster_rect.width() + padding;
         max_height = max(max_height, raster_rect.height());
     }
     let total_area = total_length * max_height;
     // Add three extra rows: One for characters that dont fit at the end of the line,
     // and another for a possibly cut of row at the bottom, and one for margin :)
     let side_length_guess = (total_area as f32).sqrt();
-    let side_length = (total_area as f32 + side_length_guess * (max_height as f32) * 3.0).sqrt() as i32;
+    let side_length = (total_area as f32 + side_length_guess * (max_height as f32) * 2.0).sqrt() as i32;
     return (side_length, side_length)
 }
 
 
-pub fn generate_atlas(font: &Font, size: f32) -> Canvas {
-    let (canvas_w, canvas_h) = estimate_atlas_size(&font, size);
+pub fn generate_atlas(font: &Font, size: f32, padding: Option<i32>) -> Canvas {
+    // 2px has been shown to be a safe minimum padding.
+    let padding = padding.unwrap_or(2);
+    let (canvas_w, canvas_h) = estimate_atlas_size(&font, size, padding);
     log::debug!("Creating font atlas with dimensions {}x{} for \"{}\", {:.1}px", canvas_w, canvas_h, font.full_name(), size);
     let mut canvas = Canvas::new(Vector2I::new(canvas_w, canvas_h), Format::Rgb24);
-    let mut transform_vec = Vector2F::new(0.0, -size);
+    let mut transform_vec = Vector2F::new(0.0, 0.0);
 
     for c in PrintableChars::new() {
-
         let glyph_id = font.glyph_for_char(c).unwrap();
+
+        // Predict raster width
         let raster_rect = font.raster_bounds(
             glyph_id, size,
-            Transform2F::from_translation(transform_vec),
+            Transform2F::default(),
             HintingOptions::Vertical(size),
             RasterizationOptions::SubpixelAa
         ).unwrap();
-        // Skip drawing this glyph if it is zero-width.
         if raster_rect.width() == 0 { continue; }
 
-        let new_x = transform_vec.x() + raster_rect.width() as f32;
-        if new_x > canvas_w as f32 {
+        // Calculate offset
+        let mut new_x = transform_vec.x() as i32 + raster_rect.width() + padding;
+        if new_x >= canvas_w {
+            new_x = raster_rect.width() + padding;
             transform_vec.set_x(0.0);
-            transform_vec.set_y(transform_vec.y() - size);
+            transform_vec.set_y(transform_vec.y() + size);
         }
+
         font.rasterize_glyph(
             &mut canvas,
             glyph_id,
             size,
-            Transform2F::from_translation(transform_vec),
+            Transform2F::from_translation(-raster_rect.origin().to_f32()) * Transform2F::from_translation(transform_vec),
             HintingOptions::Vertical(size),
             RasterizationOptions::SubpixelAa,
         ).unwrap();
 
-        transform_vec.set_x(new_x);
+        transform_vec.set_x(new_x as f32);
     }
     canvas
 }