polyscope_render/

ssaa_pass.rs

//! SSAA (Supersampling Anti-Aliasing) downsample pass.

use std::num::NonZeroU64;
use wgpu::util::DeviceExt;

/// GPU representation of SSAA downsample uniforms.
#[repr(C)]
#[derive(Debug, Clone, Copy, bytemuck::Pod, bytemuck::Zeroable)]
pub struct SsaaUniforms {
    pub ssaa_factor: u32,
    _padding: [u32; 3],
}

/// SSAA downsample render resources.
pub struct SsaaPass {
    pipeline: wgpu::RenderPipeline,
    bind_group_layout: wgpu::BindGroupLayout,
    uniform_buffer: wgpu::Buffer,
    sampler: wgpu::Sampler,
    ssaa_factor: u32,
}

impl SsaaPass {
    /// Creates a new SSAA downsample pass.
    #[must_use]
    pub fn new(device: &wgpu::Device, output_format: wgpu::TextureFormat) -> Self {
        // Create bind group layout
        let bind_group_layout = device.create_bind_group_layout(&wgpu::BindGroupLayoutDescriptor {
            label: Some("SSAA Downsample Bind Group Layout"),
            entries: &[
                // Input texture (high-res HDR)
                wgpu::BindGroupLayoutEntry {
                    binding: 0,
                    visibility: wgpu::ShaderStages::FRAGMENT,
                    ty: wgpu::BindingType::Texture {
                        sample_type: wgpu::TextureSampleType::Float { filterable: true },
                        view_dimension: wgpu::TextureViewDimension::D2,
                        multisampled: false,
                    },
                    count: None,
                },
                // Sampler
                wgpu::BindGroupLayoutEntry {
                    binding: 1,
                    visibility: wgpu::ShaderStages::FRAGMENT,
                    ty: wgpu::BindingType::Sampler(wgpu::SamplerBindingType::Filtering),
                    count: None,
                },
                // Uniforms
                wgpu::BindGroupLayoutEntry {
                    binding: 2,
                    visibility: wgpu::ShaderStages::FRAGMENT,
                    ty: wgpu::BindingType::Buffer {
                        ty: wgpu::BufferBindingType::Uniform,
                        has_dynamic_offset: false,
                        min_binding_size: NonZeroU64::new(16),
                    },
                    count: None,
                },
            ],
        });

        // Create shader
        let shader = device.create_shader_module(wgpu::ShaderModuleDescriptor {
            label: Some("SSAA Downsample Shader"),
            source: wgpu::ShaderSource::Wgsl(include_str!("shaders/ssaa_downsample.wgsl").into()),
        });

        // Create pipeline layout
        let pipeline_layout = device.create_pipeline_layout(&wgpu::PipelineLayoutDescriptor {
            label: Some("SSAA Downsample Pipeline Layout"),
            bind_group_layouts: &[&bind_group_layout],
            push_constant_ranges: &[],
        });

        // Create render pipeline
        let pipeline = device.create_render_pipeline(&wgpu::RenderPipelineDescriptor {
            label: Some("SSAA Downsample Pipeline"),
            layout: Some(&pipeline_layout),
            vertex: wgpu::VertexState {
                module: &shader,
                entry_point: Some("vs_main"),
                buffers: &[],
                compilation_options: wgpu::PipelineCompilationOptions::default(),
            },
            fragment: Some(wgpu::FragmentState {
                module: &shader,
                entry_point: Some("fs_main"),
                targets: &[Some(wgpu::ColorTargetState {
                    format: output_format,
                    blend: None,
                    write_mask: wgpu::ColorWrites::ALL,
                })],
                compilation_options: wgpu::PipelineCompilationOptions::default(),
            }),
            primitive: wgpu::PrimitiveState {
                topology: wgpu::PrimitiveTopology::TriangleList,
                ..Default::default()
            },
            depth_stencil: None,
            multisample: wgpu::MultisampleState::default(),
            multiview: None,
            cache: None,
        });

        // Create uniform buffer
        let uniforms = SsaaUniforms {
            ssaa_factor: 1,
            _padding: [0; 3],
        };
        let uniform_buffer = device.create_buffer_init(&wgpu::util::BufferInitDescriptor {
            label: Some("SSAA Uniform Buffer"),
            contents: bytemuck::cast_slice(&[uniforms]),
            usage: wgpu::BufferUsages::UNIFORM | wgpu::BufferUsages::COPY_DST,
        });

        // Create sampler with linear filtering for smooth downsampling
        let sampler = device.create_sampler(&wgpu::SamplerDescriptor {
            label: Some("SSAA Sampler"),
            mag_filter: wgpu::FilterMode::Linear,
            min_filter: wgpu::FilterMode::Linear,
            ..Default::default()
        });

        Self {
            pipeline,
            bind_group_layout,
            uniform_buffer,
            sampler,
            ssaa_factor: 1,
        }
    }

    /// Updates the SSAA factor.
    pub fn set_ssaa_factor(&mut self, queue: &wgpu::Queue, factor: u32) {
        // Clamp to valid values
        let factor = factor.clamp(1, 4);
        if factor != self.ssaa_factor {
            self.ssaa_factor = factor;
            let uniforms = SsaaUniforms {
                ssaa_factor: factor,
                _padding: [0; 3],
            };
            queue.write_buffer(&self.uniform_buffer, 0, bytemuck::cast_slice(&[uniforms]));
        }
    }

    /// Returns the current SSAA factor.
    #[must_use]
    pub fn ssaa_factor(&self) -> u32 {
        self.ssaa_factor
    }

    /// Creates a bind group for rendering.
    #[must_use]
    pub fn create_bind_group(
        &self,
        device: &wgpu::Device,
        input_view: &wgpu::TextureView,
    ) -> wgpu::BindGroup {
        device.create_bind_group(&wgpu::BindGroupDescriptor {
            label: Some("SSAA Bind Group"),
            layout: &self.bind_group_layout,
            entries: &[
                wgpu::BindGroupEntry {
                    binding: 0,
                    resource: wgpu::BindingResource::TextureView(input_view),
                },
                wgpu::BindGroupEntry {
                    binding: 1,
                    resource: wgpu::BindingResource::Sampler(&self.sampler),
                },
                wgpu::BindGroupEntry {
                    binding: 2,
                    resource: self.uniform_buffer.as_entire_binding(),
                },
            ],
        })
    }

    /// Renders the SSAA downsample pass.
    pub fn render(
        &self,
        encoder: &mut wgpu::CommandEncoder,
        output_view: &wgpu::TextureView,
        bind_group: &wgpu::BindGroup,
    ) {
        let mut render_pass = encoder.begin_render_pass(&wgpu::RenderPassDescriptor {
            label: Some("SSAA Downsample Pass"),
            color_attachments: &[Some(wgpu::RenderPassColorAttachment {
                view: output_view,
                resolve_target: None,
                ops: wgpu::Operations {
                    load: wgpu::LoadOp::Clear(wgpu::Color::BLACK),
                    store: wgpu::StoreOp::Store,
                },
                depth_slice: None,
            })],
            depth_stencil_attachment: None,
            ..Default::default()
        });

        render_pass.set_pipeline(&self.pipeline);
        render_pass.set_bind_group(0, bind_group, &[]);
        render_pass.draw(0..3, 0..1); // Fullscreen triangle
    }

    /// Renders SSAA downsample from input texture to output texture.
    /// Convenience method that creates a bind group and renders in one call.
    pub fn render_to_target(
        &self,
        device: &wgpu::Device,
        encoder: &mut wgpu::CommandEncoder,
        input_view: &wgpu::TextureView,
        output_view: &wgpu::TextureView,
    ) {
        let bind_group = self.create_bind_group(device, input_view);
        self.render(encoder, output_view, &bind_group);
    }
}