codecraft 0.1.1

use bytemuck::{Pod, Zeroable};

use super::atlas;
use wgpu::util::DeviceExt;

/// One flat-colored, axis-aligned rectangle in screen (pixel) space.
#[repr(C)]
#[derive(Clone, Copy, Pod, Zeroable)]
pub struct QuadInstance {
    pub pos: [f32; 2],
    pub size: [f32; 2],
    pub color: [f32; 4],
    /// The rectangle of the icon atlas to sample, as `[u0, v0, u1, v1]`.
    ///
    /// An empty rectangle -- which is what [`Default`] gives, and what every
    /// panel, button and glyph uses -- means a flat colour and no sampling at
    /// all. Icons are the exception, not the rule, so they are the ones that
    /// have to say something.
    pub uv: [f32; 4],
}

/// The `uv` of a quad that is a flat colour rather than an icon.
pub const NO_ICON: [f32; 4] = [0.0; 4];

#[repr(C)]
#[derive(Clone, Copy, Pod, Zeroable)]
struct ScreenUniform {
    size: [f32; 2],
    _pad: [f32; 2],
}

const UNIT_QUAD: &[[f32; 2]] = &[[0.0, 0.0], [1.0, 0.0], [0.0, 1.0], [1.0, 1.0]];

/// Draws a batch of [`QuadInstance`]s in a single instanced draw call.
///
/// Used to render UI widgets (button/panel backgrounds, bitmap-font glyphs)
/// as flat-colored rectangles in screen space.
pub struct UiRenderer {
    pipeline: wgpu::RenderPipeline,
    unit_quad_buffer: wgpu::Buffer,
    instance_buffer: wgpu::Buffer,
    instance_capacity: usize,
    screen_uniform_buffer: wgpu::Buffer,
    bind_group: wgpu::BindGroup,
    atlas: wgpu::Texture,
}

impl UiRenderer {
    pub fn new(device: &wgpu::Device, format: wgpu::TextureFormat) -> Self {
        let shader = device.create_shader_module(wgpu::ShaderModuleDescriptor {
            label: Some("ui shader"),
            source: wgpu::ShaderSource::Wgsl(include_str!("ui.wgsl").into()),
        });

        let screen_uniform_buffer = device.create_buffer(&wgpu::BufferDescriptor {
            label: Some("ui screen uniform"),
            size: std::mem::size_of::<ScreenUniform>() as u64,
            usage: wgpu::BufferUsages::UNIFORM | wgpu::BufferUsages::COPY_DST,
            mapped_at_creation: false,
        });

        let bind_group_layout = device.create_bind_group_layout(&wgpu::BindGroupLayoutDescriptor {
            label: Some("ui bind group layout"),
            entries: &[
                wgpu::BindGroupLayoutEntry {
                    binding: 0,
                    visibility: wgpu::ShaderStages::VERTEX,
                    ty: wgpu::BindingType::Buffer {
                        ty: wgpu::BufferBindingType::Uniform,
                        has_dynamic_offset: false,
                        min_binding_size: None,
                    },
                    count: None,
                },
                wgpu::BindGroupLayoutEntry {
                    binding: 1,
                    visibility: wgpu::ShaderStages::FRAGMENT,
                    ty: wgpu::BindingType::Texture {
                        sample_type: wgpu::TextureSampleType::Float { filterable: true },
                        view_dimension: wgpu::TextureViewDimension::D2,
                        multisampled: false,
                    },
                    count: None,
                },
                wgpu::BindGroupLayoutEntry {
                    binding: 2,
                    visibility: wgpu::ShaderStages::FRAGMENT,
                    ty: wgpu::BindingType::Sampler(wgpu::SamplerBindingType::Filtering),
                    count: None,
                },
            ],
        });

        // The atlas the UI samples: icons and glyphs, both white masks. Made
        // empty and filled as they are asked for; see `ui::atlas`.
        let atlas = device.create_texture(&wgpu::TextureDescriptor {
            label: Some("ui atlas"),
            size: wgpu::Extent3d {
                width: atlas::ATLAS_SIZE,
                height: atlas::ATLAS_SIZE,
                depth_or_array_layers: 1,
            },
            mip_level_count: 1,
            sample_count: 1,
            dimension: wgpu::TextureDimension::D2,
            // The mask is coverage, not colour, so it is linear: read it as
            // sRGB and every anti-aliased edge darkens.
            format: wgpu::TextureFormat::Rgba8Unorm,
            usage: wgpu::TextureUsages::TEXTURE_BINDING | wgpu::TextureUsages::COPY_DST,
            view_formats: &[],
        });
        let atlas_view = atlas.create_view(&wgpu::TextureViewDescriptor::default());
        let atlas_sampler = device.create_sampler(&wgpu::SamplerDescriptor {
            label: Some("ui atlas sampler"),
            mag_filter: wgpu::FilterMode::Linear,
            min_filter: wgpu::FilterMode::Linear,
            ..Default::default()
        });

        let bind_group = device.create_bind_group(&wgpu::BindGroupDescriptor {
            label: Some("ui bind group"),
            layout: &bind_group_layout,
            entries: &[
                wgpu::BindGroupEntry {
                    binding: 0,
                    resource: screen_uniform_buffer.as_entire_binding(),
                },
                wgpu::BindGroupEntry {
                    binding: 1,
                    resource: wgpu::BindingResource::TextureView(&atlas_view),
                },
                wgpu::BindGroupEntry {
                    binding: 2,
                    resource: wgpu::BindingResource::Sampler(&atlas_sampler),
                },
            ],
        });

        let pipeline_layout = device.create_pipeline_layout(&wgpu::PipelineLayoutDescriptor {
            label: Some("ui pipeline layout"),
            bind_group_layouts: &[Some(&bind_group_layout)],
            immediate_size: 0,
        });

        let unit_quad_layout = wgpu::VertexBufferLayout {
            array_stride: std::mem::size_of::<[f32; 2]>() as wgpu::BufferAddress,
            step_mode: wgpu::VertexStepMode::Vertex,
            attributes: &wgpu::vertex_attr_array![0 => Float32x2],
        };

        let instance_layout = wgpu::VertexBufferLayout {
            array_stride: std::mem::size_of::<QuadInstance>() as wgpu::BufferAddress,
            step_mode: wgpu::VertexStepMode::Instance,
            attributes: &wgpu::vertex_attr_array![
                1 => Float32x2, 2 => Float32x2, 3 => Float32x4, 4 => Float32x4
            ],
        };

        let pipeline = device.create_render_pipeline(&wgpu::RenderPipelineDescriptor {
            label: Some("ui pipeline"),
            layout: Some(&pipeline_layout),
            vertex: wgpu::VertexState {
                module: &shader,
                entry_point: Some("vs_main"),
                buffers: &[Some(unit_quad_layout), Some(instance_layout)],
                compilation_options: wgpu::PipelineCompilationOptions::default(),
            },
            fragment: Some(wgpu::FragmentState {
                module: &shader,
                entry_point: Some("fs_main"),
                targets: &[Some(wgpu::ColorTargetState {
                    format,
                    blend: Some(wgpu::BlendState::ALPHA_BLENDING),
                    write_mask: wgpu::ColorWrites::ALL,
                })],
                compilation_options: wgpu::PipelineCompilationOptions::default(),
            }),
            primitive: wgpu::PrimitiveState {
                topology: wgpu::PrimitiveTopology::TriangleStrip,
                strip_index_format: None,
                front_face: wgpu::FrontFace::Ccw,
                cull_mode: None,
                polygon_mode: wgpu::PolygonMode::Fill,
                unclipped_depth: false,
                conservative: false,
            },
            depth_stencil: None,
            multisample: wgpu::MultisampleState::default(),
            multiview_mask: None,
            cache: None,
        });

        let unit_quad_buffer = device.create_buffer_init(&wgpu::util::BufferInitDescriptor {
            label: Some("ui unit quad"),
            contents: bytemuck::cast_slice(UNIT_QUAD),
            usage: wgpu::BufferUsages::VERTEX,
        });

        let instance_capacity = 256;
        let instance_buffer = device.create_buffer(&wgpu::BufferDescriptor {
            label: Some("ui instances"),
            size: (instance_capacity * std::mem::size_of::<QuadInstance>()) as u64,
            usage: wgpu::BufferUsages::VERTEX | wgpu::BufferUsages::COPY_DST,
            mapped_at_creation: false,
        });

        Self {
            pipeline,
            unit_quad_buffer,
            instance_buffer,
            instance_capacity,
            screen_uniform_buffer,
            bind_group,
            atlas,
        }
    }

    /// Sends the icon atlas, if it has changed since the last frame.
    ///
    /// The whole square goes rather than the one slot that moved: it is a
    /// megabyte, it happens only on the frames a panel first asks for an icon
    /// it has never drawn, and a partial write would have to know the slot.
    pub fn upload_atlas(&self, queue: &wgpu::Queue, atlas: &mut atlas::Atlas) {
        let Some(pixels) = atlas.take_if_dirty() else {
            return;
        };
        queue.write_texture(
            self.atlas.as_image_copy(),
            pixels,
            wgpu::TexelCopyBufferLayout {
                offset: 0,
                bytes_per_row: Some(atlas::ATLAS_SIZE * 4),
                rows_per_image: Some(atlas::ATLAS_SIZE),
            },
            wgpu::Extent3d {
                width: atlas::ATLAS_SIZE,
                height: atlas::ATLAS_SIZE,
                depth_or_array_layers: 1,
            },
        );
    }

    fn ensure_capacity(&mut self, device: &wgpu::Device, needed: usize) {
        if needed <= self.instance_capacity {
            return;
        }
        self.instance_capacity = needed.next_power_of_two();
        self.instance_buffer = device.create_buffer(&wgpu::BufferDescriptor {
            label: Some("ui instances"),
            size: (self.instance_capacity * std::mem::size_of::<QuadInstance>()) as u64,
            usage: wgpu::BufferUsages::VERTEX | wgpu::BufferUsages::COPY_DST,
            mapped_at_creation: false,
        });
    }

    /// Clears `view` to `clear_color` and draws `quads` on top of it.
    #[allow(clippy::too_many_arguments)]
    pub fn render(
        &mut self,
        device: &wgpu::Device,
        queue: &wgpu::Queue,
        encoder: &mut wgpu::CommandEncoder,
        view: &wgpu::TextureView,
        screen_width: f32,
        screen_height: f32,
        quads: &[QuadInstance],
    ) {
        let screen_uniform = ScreenUniform {
            size: [screen_width, screen_height],
            _pad: [0.0, 0.0],
        };
        queue.write_buffer(
            &self.screen_uniform_buffer,
            0,
            bytemuck::bytes_of(&screen_uniform),
        );

        if !quads.is_empty() {
            self.ensure_capacity(device, quads.len());
            queue.write_buffer(&self.instance_buffer, 0, bytemuck::cast_slice(quads));
        }

        let mut pass = encoder.begin_render_pass(&wgpu::RenderPassDescriptor {
            label: Some("ui render pass"),
            color_attachments: &[Some(wgpu::RenderPassColorAttachment {
                view,
                resolve_target: None,
                depth_slice: None,
                ops: wgpu::Operations {
                    // The 3D pass has already cleared and drawn the world.
                    load: wgpu::LoadOp::Load,
                    store: wgpu::StoreOp::Store,
                },
            })],
            depth_stencil_attachment: None,
            timestamp_writes: None,
            occlusion_query_set: None,
            multiview_mask: None,
        });

        if quads.is_empty() {
            return;
        }

        pass.set_pipeline(&self.pipeline);
        pass.set_bind_group(0, &self.bind_group, &[]);
        pass.set_vertex_buffer(0, self.unit_quad_buffer.slice(..));
        pass.set_vertex_buffer(1, self.instance_buffer.slice(..));
        pass.draw(0..4, 0..quads.len() as u32);
    }
}