Add a plotter example using plotters

This is kind of an interactive port of
https://github.com/38/plotters/blob/master/examples/3d-plot2.rs

examples/plotter/Cargo.toml

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+[package]
+name = "plotter"
+version = "0.1.0"
+authors = ["SixtyFPS <info@sixtyfps.io>"]
+edition = "2018"
+publish = false
+license = "GPL-3.0-only"
+
+[[bin]]
+path = "main.rs"
+name = "plotter"
+
+[dependencies]
+sixtyfps = { path = "../../api/sixtyfps-rs" }
+#plotters = { version = "0.3.1", default-features = false, features = ["bitmap"] }
+plotters = { version = "0.3.1", default-features = false, features = ["bitmap_backend", "surface_series"] }
+imgref = "1"
+rgb = "0.8.27"
+
+[build-dependencies]
+sixtyfps-build = { path = "../../api/sixtyfps-rs/sixtyfps-build" }
+
+# Remove the `#wasm#` to uncomment the wasm build.
+# This is commented out by default because we don't want to build it as a library by default
+# The CI has a script that does sed "s/#wasm# //" to generate the wasm build.
+
+#wasm# [lib]
+#wasm# path = "main.rs"
+#wasm# crate-type = ["cdylib"]
+
+#wasm# [target.'cfg(target_arch = "wasm32")'.dependencies]
+#wasm# wasm-bindgen = { version = "0.2" }
+#wasm# web-sys = { version = "0.3", features=["console"] }
+#wasm# console_error_panic_hook = "0.1.5"
+#wasm# getrandom = { version = "0.2.2", features = ["js"] }

examples/plotter/main.rs

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+/* LICENSE BEGIN
+    This file is part of the SixtyFPS Project -- https://sixtyfps.io
+    Copyright (c) 2021 Olivier Goffart <olivier.goffart@sixtyfps.io>
+    Copyright (c) 2021 Simon Hausmann <simon.hausmann@sixtyfps.io>
+
+    SPDX-License-Identifier: GPL-3.0-only
+    This file is also available under commercial licensing terms.
+    Please contact info@sixtyfps.io for more information.
+LICENSE END */
+
+use plotters::prelude::*;
+use rgb::ComponentBytes;
+use sixtyfps::SharedPixelBuffer;
+
+#[cfg(target_arch = "wasm32")]
+use wasm_bindgen::prelude::*;
+
+sixtyfps::sixtyfps! {
+    import { MainWindow } from "plotter.60";
+}
+
+fn pdf(x: f64, y: f64) -> f64 {
+    const SDX: f64 = 0.1;
+    const SDY: f64 = 0.1;
+    const A: f64 = 5.0;
+    let x = x as f64 / 10.0;
+    let y = y as f64 / 10.0;
+    A * (-x * x / 2.0 / SDX / SDX - y * y / 2.0 / SDY / SDY).exp()
+}
+
+fn render_plot(pitch: f32) -> sixtyfps::Image {
+    let mut pixel_buffer = SharedPixelBuffer::<rgb::RGB8>::new(640, 480);
+    let size = (pixel_buffer.width() as u32, pixel_buffer.height() as u32);
+
+    let root = BitMapBackend::with_buffer(pixel_buffer.as_mut_slice().as_bytes_mut(), size)
+        .into_drawing_area();
+
+    root.fill(&WHITE).expect("error filling drawing area");
+
+    let mut chart = ChartBuilder::on(&root)
+        .build_cartesian_3d(-3.0..3.0, 0.0..6.0, -3.0..3.0)
+        .expect("error building coordinate system");
+    chart.with_projection(|mut p| {
+        p.pitch = 1.57 - (1.57 - pitch as f64 / 50.0).abs();
+        p.scale = 0.7;
+        p.into_matrix() // build the projection matrix
+    });
+
+    chart.configure_axes().draw().expect("error drawing");
+
+    chart
+        .draw_series(
+            SurfaceSeries::xoz(
+                (-15..=15).map(|x| x as f64 / 5.0),
+                (-15..=15).map(|x| x as f64 / 5.0),
+                pdf,
+            )
+            .style_func(&|&v| {
+                (&HSLColor(240.0 / 360.0 - 240.0 / 360.0 * v / 5.0, 1.0, 0.7)).into()
+            }),
+        )
+        .expect("error drawing series");
+
+    root.present().expect("error presenting");
+    drop(chart);
+    drop(root);
+
+    sixtyfps::SharedImageBuffer::RGB8(pixel_buffer).into()
+}
+
+#[cfg_attr(target_arch = "wasm32", wasm_bindgen(start))]
+pub fn main() {
+    // This provides better error messages in debug mode.
+    // It's disabled in release mode so it doesn't bloat up the file size.
+    #[cfg(all(debug_assertions, target_arch = "wasm32"))]
+    console_error_panic_hook::set_once();
+
+    let main_window = MainWindow::new();
+
+    main_window.on_redraw({
+        let main_window_weak = main_window.as_weak();
+        move || {
+            let main_window = main_window_weak.upgrade().unwrap();
+            let plot = render_plot(main_window.get_pitch());
+            main_window.set_plot_image(plot);
+        }
+    });
+
+    main_window.invoke_redraw();
+
+    main_window.run();
+}

examples/plotter/plotter.60

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+/* LICENSE BEGIN
+    This file is part of the SixtyFPS Project -- https://sixtyfps.io
+    Copyright (c) 2021 Olivier Goffart <olivier.goffart@sixtyfps.io>
+    Copyright (c) 2021 Simon Hausmann <simon.hausmann@sixtyfps.io>
+
+    SPDX-License-Identifier: GPL-3.0-only
+    This file is also available under commercial licensing terms.
+    Please contact info@sixtyfps.io for more information.
+LICENSE END */
+import { Slider, GroupBox } from "sixtyfps_widgets.60";
+
+export MainWindow := Window {
+    title: "SixtyFPS Plotter Integration Example";
+    preferred-width: 800px;
+    preferred-height: 600px;
+
+    property plot_image <=> img.source;
+    property pitch <=> pitch_slider.value;
+    callback redraw();
+
+    VerticalLayout {
+        Text {
+            font-size: 20px;
+            text: "2D Gaussian PDF";
+            horizontal-alignment: center;
+        }
+        img := Image {
+        }
+        GroupBox {
+            title: "Pitch";
+            pitch_slider := Slider {
+                minimum: 0;
+                maximum: 180;
+                value: 42;
+                changed => { root.redraw(); }
+            }
+        }
+
+    }
+}