Hacked version of canvas_minimal to demonstrate an artifact when rendering overlapping paths

path_artifacts.rs

//pathfinder/examples/canvas_minimal/src/main.rs
//
// Copyright © 2019 The Pathfinder Project Developers.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

use euclid::default::Size2D;
use pathfinder_canvas::{Canvas, CanvasFontContext, Path2D, FillRule};
use pathfinder_color::{ColorF, ColorU};
use pathfinder_geometry::rect::RectF;
use pathfinder_geometry::vector::{vec2f, vec2i};
use pathfinder_gl::{GLDevice, GLVersion};
use pathfinder_renderer::concurrent::rayon::RayonExecutor;
use pathfinder_renderer::concurrent::scene_proxy::SceneProxy;
use pathfinder_renderer::gpu::options::{DestFramebuffer, RendererMode, RendererOptions};
use pathfinder_renderer::gpu::renderer::Renderer;
use pathfinder_renderer::options::BuildOptions;
use pathfinder_resources::embedded::EmbeddedResourceLoader;
use surfman::{Connection, ContextAttributeFlags, ContextAttributes, GLVersion as SurfmanGLVersion};
use surfman::{SurfaceAccess, SurfaceType};
use winit::dpi::LogicalSize;
use winit::{ControlFlow, Event, EventsLoop, WindowBuilder, WindowEvent};

fn main() {
    // Open a window.
    let mut event_loop = EventsLoop::new();
    let window_size = Size2D::new(640, 480);
    let logical_size = LogicalSize::new(window_size.width as f64, window_size.height as f64);
    let window = WindowBuilder::new().with_title("Minimal example")
                                     .with_dimensions(logical_size)
                                     .build(&event_loop)
                                     .unwrap();
    window.show();

    // Create a `surfman` device. On a multi-GPU system, we'll request the low-power integrated
    // GPU.
    let connection = Connection::from_winit_window(&window).unwrap();
    let native_widget = connection.create_native_widget_from_winit_window(&window).unwrap();
    let adapter = connection.create_low_power_adapter().unwrap();
    let mut device = connection.create_device(&adapter).unwrap();

    // Request an OpenGL 3.x context. Pathfinder requires this.
    let context_attributes = ContextAttributes {
        version: SurfmanGLVersion::new(3, 0),
        flags: ContextAttributeFlags::ALPHA,
    };
    let context_descriptor = device.create_context_descriptor(&context_attributes).unwrap();

    // Make the OpenGL context via `surfman`, and load OpenGL functions.
    let surface_type = SurfaceType::Widget { native_widget };
    let mut context = device.create_context(&context_descriptor).unwrap();
    let surface = device.create_surface(&context, SurfaceAccess::GPUOnly, surface_type)
                        .unwrap();
    device.bind_surface_to_context(&mut context, surface).unwrap();
    device.make_context_current(&context).unwrap();
    gl::load_with(|symbol_name| device.get_proc_address(&context, symbol_name));

    // Get the real size of the window, taking HiDPI into account.
    let hidpi_factor = window.get_current_monitor().get_hidpi_factor();
    let physical_size = logical_size.to_physical(hidpi_factor);
    let framebuffer_size = vec2i(physical_size.width as i32, physical_size.height as i32);

    // Create a Pathfinder GL device.
    let default_framebuffer = device.context_surface_info(&context)
                                    .unwrap()
                                    .unwrap()
                                    .framebuffer_object;
    let pathfinder_device = GLDevice::new(GLVersion::GL3, default_framebuffer);

    // Create a Pathfinder renderer.
    let mode = RendererMode::default_for_device(&pathfinder_device);
    let options = RendererOptions {
        dest: DestFramebuffer::full_window(framebuffer_size),
        background_color: Some(ColorF::white()),
        ..RendererOptions::default()
    };
    let resource_loader = EmbeddedResourceLoader::new();
    let mut renderer = Renderer::new(pathfinder_device, &resource_loader, mode, options);

    // Make a canvas. We're going to draw a house.
    let font_context = CanvasFontContext::from_system_source();
    let mut canvas = Canvas::new(framebuffer_size.to_f32()).get_context_2d(font_context);

    canvas.set_fill_style(ColorU::new(255, 0, 0, 255));
    for x in 0..10000 {
        for y in 0..1 {
            let x = x as f32 * 0.0;
            let y = y as f32 * 0.0;
            let mut path = Path2D::new();
            path.move_to(vec2f(x +50.0, y  + 140.0));
            path.line_to(vec2f(x +150.0, y  + 60.0));
            path.line_to(vec2f(x +250.0, y  + 140.0));
            path.line_to(vec2f(x +50.0, y  + 140.0));
            //path.close_path();
            canvas.fill_path(path, FillRule::Winding);
        }
    }

    // Render the canvas to screen.
    let mut scene = SceneProxy::from_scene(canvas.into_canvas().into_scene(),
                                           renderer.mode().level,
                                           RayonExecutor);
    scene.build_and_render(&mut renderer, BuildOptions::default());

    // Present the surface.
    let mut surface = device.unbind_surface_from_context(&mut context).unwrap().unwrap();
    device.present_surface(&mut context, &mut surface).unwrap();
    device.bind_surface_to_context(&mut context, surface).unwrap();

    // Wait for a keypress.
    event_loop.run_forever(|event| {
        match event {
            Event::WindowEvent { event: WindowEvent::CloseRequested, .. } |
            Event::WindowEvent { event: WindowEvent::KeyboardInput { .. }, .. } => {
                ControlFlow::Continue
            }
            _ => ControlFlow::Continue,
        }
    });

    // Clean up.
    drop(device.destroy_context(&mut context));
}