Add tests workflow

.github/workflows/tests.yml

@@ -0,0 +1,26 @@
+name: Run Tests
+on:
+  push: {}
+  pull_request: {}
+
+jobs:
+  test:
+    timeout-minutes: 30
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: install native dependencies
+        run: sudo apt-get update; sudo apt-get install libgtk-3-dev
+
+      - name: Run tests
+        run: cargo test --package plotters-piet
+        # For now we skip the plotters-druid tests because the latest druid
+        # version currently depends on a pre-release version of piet.
+
+      - uses: actions/upload-artifact@v4
+        if: failure()
+        with:
+          name: images
+          path: ./**/tests/**/*.png

plotters-piet/Cargo.toml

@@ -21,3 +21,4 @@ plotters-backend = "^0.3"
 [dev-dependencies]
 plotters = "^0.3"
 piet-common = {version = "0.6.1", features = ["png"]}
+image = { version = "0.24.9", default-features = false, features = ["png"] }

plotters-piet/tests/snowflake.rs

@@ -0,0 +1,97 @@
+use image::RgbaImage;
+use piet_common::{BitmapTarget, Device, ImageFormat};
+use plotters::prelude::*;
+use plotters_piet::PietBackend;
+
+// Copied from the plotters "Snowflake" example:
+// https://github.com/plotters-rs/plotters/blob/0f195eadaac7d9a2390a3707fbe192f8e2645d34/plotters/examples/snowflake.rs
+
+#[test]
+fn snapshot_test() {
+    let width = 600;
+    let height = 450;
+
+    let mut device = Device::new().unwrap();
+    let mut bitmap = device.bitmap_target(width, height, 1.0).unwrap();
+
+    {
+        let mut render_ctx = bitmap.render_context();
+        let piet_backend = PietBackend {
+            size: (width as u32, height as u32),
+            render_ctx: &mut render_ctx,
+        };
+
+        let root = piet_backend.into_drawing_area();
+
+        root.fill(&WHITE).unwrap();
+
+        let mut chart = ChartBuilder::on(&root)
+            .build_cartesian_2d(-2.0..2.0, -1.5..1.5)
+            .unwrap();
+
+        let mut snowflake_vertices = {
+            let mut current: Vec<(f64, f64)> = vec![
+                (0.0, 1.0),
+                ((3.0f64).sqrt() / 2.0, -0.5),
+                (-(3.0f64).sqrt() / 2.0, -0.5),
+            ];
+            for _ in 0..6 {
+                current = snowflake_iter(&current[..]);
+            }
+            current
+        };
+
+        chart
+            .draw_series(std::iter::once(Polygon::new(
+                snowflake_vertices.clone(),
+                RED.mix(0.2),
+            )))
+            .unwrap();
+        snowflake_vertices.push(snowflake_vertices[0]);
+        chart
+            .draw_series(std::iter::once(PathElement::new(snowflake_vertices, RED)))
+            .unwrap();
+
+        root.present().unwrap();
+    }
+
+    let expected = image::load_from_memory(include_bytes!("snowflake.png"))
+        .expect("cannot decode snapshot")
+        .into_rgba8();
+
+    let actual = bitmap_to_image(&mut bitmap);
+
+    if expected != actual {
+        actual.save("tests/snowflake-actual.png").unwrap();
+        // assert_eq would spam the console with the entire list of bytes on fails
+        assert!(false, "images differ");
+    }
+}
+
+fn snowflake_iter(points: &[(f64, f64)]) -> Vec<(f64, f64)> {
+    let mut ret = vec![];
+    for i in 0..points.len() {
+        let (start, end) = (points[i], points[(i + 1) % points.len()]);
+        let t = ((end.0 - start.0) / 3.0, (end.1 - start.1) / 3.0);
+        let s = (
+            t.0 * 0.5 - t.1 * (0.75f64).sqrt(),
+            t.1 * 0.5 + (0.75f64).sqrt() * t.0,
+        );
+        ret.push(start);
+        ret.push((start.0 + t.0, start.1 + t.1));
+        ret.push((start.0 + t.0 + s.0, start.1 + t.1 + s.1));
+        ret.push((start.0 + t.0 * 2.0, start.1 + t.1 * 2.0));
+    }
+    ret
+}
+
+fn bitmap_to_image(bitmap: &mut BitmapTarget) -> RgbaImage {
+    let buffer = bitmap.to_image_buf(ImageFormat::RgbaPremul).unwrap();
+
+    RgbaImage::from_raw(
+        buffer.width() as u32,
+        buffer.height() as u32,
+        buffer.raw_pixels().to_vec(),
+    )
+    .unwrap()
+}