Add minimal shaping and scaling example

.gitignore

@@ -1,3 +1,6 @@
 Cargo.lock
 /target
 .DS_Store
+
+# Output from running examples
+/examples/*.png

Cargo.toml

@@ -21,3 +21,6 @@ render = ["scale", "zeno/eval"]
 yazi = { version = "0.1.6", optional = true }
 zeno = { version = "0.2.2", optional = true, default_features = false }
 skrifa = { version = "0.19.3" }
+
+[dev-dependencies]
+image = "0.25" # Used by examples

examples/assets/Roboto/LICENSE.txt

@@ -0,0 +1,202 @@
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examples/assets/Roboto/README.md

@@ -0,0 +1,3 @@
+# Roboto
+
+Accessed from [Google Fonts](https://fonts.google.com/specimen/Roboto) on 2024-06-21. See [LICENCE.txt](LICENSE.txt) for licensing information.

examples/minimal.rs

@@ -0,0 +1,166 @@
+use image::{ImageBuffer, RgbaImage};
+use swash::scale::{Render, ScaleContext, Source, StrikeWith};
+use swash::shape::ShapeContext;
+use swash::text::cluster::{CharCluster, Parser, Token};
+use swash::text::Script;
+use swash::zeno::Format;
+use swash::FontRef;
+
+const CANVAS_WIDTH: usize = 700;
+const CANVAS_HEIGHT: usize = 300;
+
+const FONT_SIZE: f32 = 24.0;
+
+const PATH_FONT: &str = "./examples/assets/Roboto/Roboto-Regular.ttf";
+const PATH_OUTPUT_IMAGE: &str = "./examples/minimal.png";
+
+fn main() {
+    println!("Loading font data...");
+
+    let font_data = std::fs::read(PATH_FONT).unwrap();
+    let font = FontRef::from_index(&font_data, 0).unwrap();
+
+    println!("Drawing text...");
+
+    let mut pixel_data = vec![255; CANVAS_WIDTH * CANVAS_HEIGHT * 4]; // Initialize with white
+
+    let lines = vec![
+        "Hello world!",
+        "This is another line of text.",
+        "And... here's another one.",
+    ];
+    for (idx, line) in lines.iter().enumerate() {
+        let pos_x = 20;
+        let pos_y = 30 + idx as u32 * 30;
+        render_text(line, pos_x, pos_y, &font, &mut pixel_data);
+    }
+
+    println!("Saving image...");
+
+    let img: RgbaImage =
+        ImageBuffer::from_vec(CANVAS_WIDTH as u32, CANVAS_HEIGHT as u32, pixel_data)
+            .expect("Failed to create image buffer");
+
+    img.save(PATH_OUTPUT_IMAGE).expect("Failed to save image");
+
+    println!("Done");
+}
+
+fn render_text(
+    text_content: &str,
+    pos_x: u32,
+    pos_y: u32,
+    font: &swash::FontRef,
+    pixel_data: &mut Vec<u8>,
+) {
+    let mut shape_context = ShapeContext::new();
+    let mut shaper = shape_context
+        .builder(*font)
+        .script(Script::Latin)
+        .size(FONT_SIZE)
+        .features(&[("dlig", 1)])
+        .build();
+
+    // We'll need the character map for our font
+    let charmap = font.charmap();
+    // And some storage for the cluster we're working with
+    let mut cluster = CharCluster::new();
+    // Now we build a cluster parser which takes a script and
+    // an iterator that yields a Token per character
+    let mut parser = Parser::new(
+        Script::Latin,
+        text_content.char_indices().map(|(i, ch)| Token {
+            // The character
+            ch,
+            // Offset of the character in code units
+            offset: i as u32,
+            // Length of the character in code units
+            len: ch.len_utf8() as u8,
+            // Character information
+            info: ch.into(),
+            // Pass through user data
+            data: 0,
+        }),
+    );
+    // Loop over all of the clusters
+    while parser.next(&mut cluster) {
+        // Map all of the characters in the cluster
+        // to nominal glyph identifiers
+        cluster.map(|ch| charmap.map(ch));
+        // Add the cluster to the shaper
+        shaper.add_cluster(&cluster);
+    }
+
+    let mut scale_context = ScaleContext::new();
+
+    let mut run_offset_x: f32 = 0.0;
+
+    shaper.shape_with(|cluster| {
+        cluster.glyphs.iter().for_each(|glyph| {
+            let mut scaler = scale_context
+                .builder(*font)
+                .size(FONT_SIZE)
+                .hint(true)
+                .build();
+            let image = Render::new(&[
+                Source::ColorOutline(0),
+                Source::ColorBitmap(StrikeWith::BestFit),
+                Source::Outline,
+            ])
+            .format(Format::Subpixel)
+            .render(&mut scaler, glyph.id)
+            .unwrap();
+
+            let glyph_image_data = image.data.as_slice();
+
+            let glyph_x_min: i32 = image.placement.left;
+            let glyph_x_max: i32 = image.placement.left + image.placement.width as i32;
+            let glyph_y_min: i32 = image.placement.top;
+            let glyph_y_max: i32 = image.placement.top + image.placement.height as i32;
+
+            for glyph_x in glyph_x_min..glyph_x_max {
+                for glyph_y in glyph_y_min..glyph_y_max {
+                    // Get the value of this pixel
+                    let glyph_byte_offset = (glyph_x - glyph_x_min
+                        + (glyph_y - glyph_y_min) * image.placement.width as i32)
+                        * 4;
+
+                    if glyph_byte_offset < 0 {
+                        eprintln!("Glyph byte offset is less than 0, cannot lookup pixel data");
+                        panic!("Invalid glyph byte offset");
+                    }
+
+                    let glyph_byte_offset = glyph_byte_offset as usize;
+
+                    let pixel_r = 255 - glyph_image_data[glyph_byte_offset];
+                    let pixel_g = 255 - glyph_image_data[glyph_byte_offset + 1];
+                    let pixel_b = 255 - glyph_image_data[glyph_byte_offset + 2];
+
+                    if pixel_r == 255 && pixel_g == 255 && pixel_b == 255 {
+                        // Blank pixel, skip
+                        continue;
+                    }
+
+                    // Copy the value onto the canvas, at an offset position
+                    let canvas_x = glyph_x + pos_x as i32 + run_offset_x.round() as i32; // TODO: I think we might be missing a glyph offset
+                    let canvas_y = glyph_y + pos_y as i32 - (glyph_y_min * 2);
+
+                    let canvas_byte_offset = (canvas_y * (CANVAS_WIDTH as i32) + canvas_x) * 4;
+
+                    if canvas_byte_offset < 0 {
+                        eprintln!("canvas byte offset is less than 0, cannot set pixel data");
+                        panic!("Invalid canvas byte offset");
+                    }
+
+                    let canvas_byte_offset = canvas_byte_offset as usize;
+
+                    pixel_data[canvas_byte_offset] = pixel_r;
+                    pixel_data[canvas_byte_offset + 1] = pixel_g;
+                    pixel_data[canvas_byte_offset + 2] = pixel_b;
+                }
+            }
+
+            run_offset_x += glyph.advance.round();
+        });
+    });
+}