# surface.rs - source
Source of the Rust file `maplibre/src/render/resource/surface.rs`.
Keywords: rust, rustlang, rust-lang

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    //! Utilities for handling surfaces which can be either headless or headed. A headed surface has
    //! a handle to a window. A headless surface renders to a texture.

    use crate::render::resource::texture::TextureView;
    use crate::render::settings::RendererSettings;
    use crate::render::util::HasChanged;
    use crate::window::HeadedMapWindow;
    use crate::{MapWindow, MapWindowConfig, WindowSize};
    use std::fs::File;
    use std::io::Write;
    use std::mem::size_of;
    use std::sync::Arc;

    pub struct BufferDimensions {
        pub width: usize,
        pub height: usize,
        pub unpadded_bytes_per_row: usize,
        pub padded_bytes_per_row: usize,
    }

    impl BufferDimensions {
        fn new(width: usize, height: usize) -> Self {
            let bytes_per_pixel = size_of::<u32>();
            let unpadded_bytes_per_row = width * bytes_per_pixel;
            let align = wgpu::COPY_BYTES_PER_ROW_ALIGNMENT as usize;
            let padded_bytes_per_row_padding = (align - unpadded_bytes_per_row % align) % align;
            let padded_bytes_per_row = unpadded_bytes_per_row + padded_bytes_per_row_padding;
            Self {
                width,
                height,
                unpadded_bytes_per_row,
                padded_bytes_per_row,
            }
        }
    }

    pub struct WindowHead {
        surface: wgpu::Surface,
        surface_config: wgpu::SurfaceConfiguration,
    }

    impl WindowHead {
        pub fn configure(&self, device: &wgpu::Device) {
            self.surface.configure(device, &self.surface_config);
        }

        pub fn recreate_surface<MW>(&mut self, window: &MW, instance: &wgpu::Instance)
        where
            MW: MapWindow + HeadedMapWindow,
        {
            self.surface = unsafe { instance.create_surface(window.inner()) };
        }
        pub fn surface(&self) -> &wgpu::Surface {
            &self.surface
        }
    }

    pub struct BufferedTextureHead {
        pub texture: wgpu::Texture,
        pub output_buffer: wgpu::Buffer,
        pub buffer_dimensions: BufferDimensions,
    }

    #[cfg(feature = "headless")]
    impl BufferedTextureHead {
        pub async fn create_png<'a>(
            &self,
            device: &wgpu::Device,
            png_output_path: &str,
            // device: &wgpu::Device,
        ) {
            // Note that we're not calling `.await` here.
            let buffer_slice = self.output_buffer.slice(..);
            let buffer_future = buffer_slice.map_async(wgpu::MapMode::Read, |_| ());

            // Poll the device in a blocking manner so that our future resolves.
            // In an actual application, `device.poll(...)` should
            // be called in an event loop or on another thread.
            device.poll(wgpu::Maintain::Wait);
            let padded_buffer = buffer_slice.get_mapped_range();

            let mut png_encoder = png::Encoder::new(
                File::create(png_output_path).unwrap(),
                self.buffer_dimensions.width as u32,
                self.buffer_dimensions.height as u32,
            );
            png_encoder.set_depth(png::BitDepth::Eight);
            png_encoder.set_color(png::ColorType::Rgba);
            let mut png_writer = png_encoder
                .write_header()
                .unwrap()
                .into_stream_writer_with_size(self.buffer_dimensions.unpadded_bytes_per_row)
                .unwrap();

            // from the padded_buffer we write just the unpadded bytes into the image
            for chunk in padded_buffer.chunks(self.buffer_dimensions.padded_bytes_per_row) {
                png_writer
                    .write_all(&chunk[..self.buffer_dimensions.unpadded_bytes_per_row])
                    .unwrap();
            }
            png_writer.finish().unwrap();

            // With the current interface, we have to make sure all mapped views are
            // dropped before we unmap the buffer.
            drop(padded_buffer);

            self.output_buffer.unmap();
        }
    }

    pub enum Head {
        Headed(WindowHead),
        Headless(Arc<BufferedTextureHead>),
    }

    pub struct Surface {
        size: WindowSize,
        head: Head,
    }

    impl Surface {
        pub fn from_window<MW>(
            instance: &wgpu::Instance,
            window: &MW,
            settings: &RendererSettings,
        ) -> Self
        where
            MW: MapWindow + HeadedMapWindow,
        {
            let size = window.size();
            let surface_config = wgpu::SurfaceConfiguration {
                usage: wgpu::TextureUsages::RENDER_ATTACHMENT,
                format: settings.texture_format,
                width: size.width(),
                height: size.height(),
                //present_mode: wgpu::PresentMode::Immediate,
                present_mode: wgpu::PresentMode::Fifo, // VSync
            };

            let surface = unsafe { instance.create_surface(window.inner()) };

            Self {
                size,
                head: Head::Headed(WindowHead {
                    surface,
                    surface_config,
                }),
            }
        }

        // TODO: Give better name
        pub fn from_image<MW>(device: &wgpu::Device, window: &MW, settings: &RendererSettings) -> Self
        where
            MW: MapWindow,
        {
            let size = window.size();

            // It is a WebGPU requirement that ImageCopyBuffer.layout.bytes_per_row % wgpu::COPY_BYTES_PER_ROW_ALIGNMENT == 0
            // So we calculate padded_bytes_per_row by rounding unpadded_bytes_per_row
            // up to the next multiple of wgpu::COPY_BYTES_PER_ROW_ALIGNMENT.
            // https://en.wikipedia.org/wiki/Data_structure_alignment#Computing_padding
            let buffer_dimensions =
                BufferDimensions::new(size.width() as usize, size.height() as usize);
            // The output buffer lets us retrieve the data as an array
            let output_buffer = device.create_buffer(&wgpu::BufferDescriptor {
                label: Some("BufferedTextureHead buffer"),
                size: (buffer_dimensions.padded_bytes_per_row * buffer_dimensions.height) as u64,
                usage: wgpu::BufferUsages::MAP_READ | wgpu::BufferUsages::COPY_DST,
                mapped_at_creation: false,
            });

            let texture = device.create_texture(&wgpu::TextureDescriptor {
                label: Some("Surface texture"),
                size: wgpu::Extent3d {
                    width: size.width(),
                    height: size.height(),
                    depth_or_array_layers: 1,
                },
                mip_level_count: 1,
                sample_count: 1,
                dimension: wgpu::TextureDimension::D2,
                format: settings.texture_format,
                usage: wgpu::TextureUsages::RENDER_ATTACHMENT | wgpu::TextureUsages::COPY_SRC,
            });

            Self {
                size,
                head: Head::Headless(Arc::new(BufferedTextureHead {
                    texture,
                    output_buffer,
                    buffer_dimensions,
                })),
            }
        }

        #[tracing::instrument(name = "create_view", skip_all)]
        pub fn create_view(&self, device: &wgpu::Device) -> TextureView {
            match &self.head {
                Head::Headed(window) => {
                    let WindowHead { surface, .. } = window;
                    let frame = match surface.get_current_texture() {
                        Ok(view) => view,
                        Err(wgpu::SurfaceError::Outdated) => {
                            log::warn!("surface outdated");
                            window.configure(device);
                            surface
                                .get_current_texture()
                                .expect("Error reconfiguring surface")
                        }
                        err => err.expect("Failed to acquire next swap chain texture!"),
                    };
                    frame.into()
                }
                Head::Headless(arc) => arc
                    .texture
                    .create_view(&wgpu::TextureViewDescriptor::default())
                    .into(),
            }
        }

        pub fn size(&self) -> WindowSize {
            self.size
        }

        pub fn resize(&mut self, width: u32, height: u32) {
            self.size = WindowSize::new(width, height).expect("Invalid size for resizing the surface.");
            match &mut self.head {
                Head::Headed(window) => {
                    window.surface_config.height = height;
                    window.surface_config.width = width;
                }
                Head::Headless(_) => {}
            }
        }

        pub fn reconfigure(&mut self, device: &wgpu::Device) {
            match &mut self.head {
                Head::Headed(window) => {
                    if window.has_changed(&(self.size.width(), self.size.height())) {
                        window.configure(device);
                    }
                }
                Head::Headless(_) => {}
            }
        }

        pub fn recreate<MW>(&mut self, window: &MW, instance: &wgpu::Instance)
        where
            MW: MapWindow + HeadedMapWindow,
        {
            match &mut self.head {
                Head::Headed(window_head) => {
                    if window_head.has_changed(&(self.size.width(), self.size.height())) {
                        window_head.recreate_surface(window, instance);
                    }
                }
                Head::Headless(_) => {}
            }
        }

        pub fn head(&self) -> &Head {
            &self.head
        }

        pub fn head_mut(&mut self) -> &mut Head {
            &mut self.head
        }
    }

    impl HasChanged for WindowHead {
        type Criteria = (u32, u32);

        fn has_changed(&self, criteria: &Self::Criteria) -> bool {
            self.surface_config.width != criteria.0 || self.surface_config.height != criteria.1
        }
    }