feat(renderer): add bloom and tonemap shaders

- bloom_shader.wgsl: fullscreen vertex + fs_downsample (5-tap box + bright extract) + fs_upsample (9-tap tent)
- tonemap_shader.wgsl: fullscreen vertex + fs_main (HDR+bloom combine, exposure, ACES, gamma 1/2.2)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

crates/voltex_renderer/src/bloom.rs

@@ -38,7 +38,7 @@ impl BloomResources {
     pub fn new(device: &wgpu::Device, width: u32, height: u32) -> Self {
         let mip_views = create_mip_views(device, width, height);
 
-        let uniform = BloomUniform::default();
+        let _uniform = BloomUniform::default();
         let uniform_buffer = device.create_buffer(&wgpu::BufferDescriptor {
             label: Some("Bloom Uniform Buffer"),
             size: std::mem::size_of::<BloomUniform>() as u64,

crates/voltex_renderer/src/bloom_shader.wgsl

@@ -0,0 +1,112 @@
+// Bloom pass shader.
+// Two fragment entry points:
+//   fs_downsample — 5-tap box filter with optional bright extraction
+//   fs_upsample   — 9-tap tent filter for the upsample chain
+
+// ── Group 0 ───────────────────────────────────────────────────────────────────
+
+@group(0) @binding(0) var t_input: texture_2d<f32>;
+@group(0) @binding(1) var s_input: sampler;
+
+struct BloomUniform {
+    threshold:      f32,
+    soft_threshold: f32,
+    _padding:       vec2<f32>,
+};
+
+@group(0) @binding(2) var<uniform> bloom: BloomUniform;
+
+// ── Vertex stage ──────────────────────────────────────────────────────────────
+
+struct VertexInput {
+    @location(0) position: vec2<f32>,
+};
+
+struct VertexOutput {
+    @builtin(position) clip_position: vec4<f32>,
+    @location(0)       uv:            vec2<f32>,
+};
+
+@vertex
+fn vs_main(v: VertexInput) -> VertexOutput {
+    var out: VertexOutput;
+    out.clip_position = vec4<f32>(v.position, 0.0, 1.0);
+    out.uv = vec2<f32>(v.position.x * 0.5 + 0.5, 1.0 - (v.position.y * 0.5 + 0.5));
+    return out;
+}
+
+// ── Shared helpers ────────────────────────────────────────────────────────────
+
+fn luminance(c: vec3<f32>) -> f32 {
+    return dot(c, vec3<f32>(0.2126, 0.7152, 0.0722));
+}
+
+/// Soft-knee bright-pass: returns the colour with sub-threshold values attenuated.
+fn bright_extract(color: vec3<f32>, threshold: f32, soft: f32) -> vec3<f32> {
+    let lum = luminance(color);
+    let knee = threshold * soft;
+    // Quadratic soft knee
+    let ramp = clamp(lum - threshold + knee, 0.0, 2.0 * knee);
+    let weight = select(
+        select(0.0, 1.0, lum >= threshold),
+        ramp * ramp / (4.0 * knee + 0.00001),
+        lum >= threshold - knee && lum < threshold,
+    );
+    // When lum >= threshold we pass through, otherwise fade via weight
+    if lum >= threshold {
+        return color;
+    }
+    return color * (weight / max(lum, 0.00001));
+}
+
+// ── Downsample pass ───────────────────────────────────────────────────────────
+
+/// 5-sample box filter: centre × 4 + 4 diagonal neighbours × 1, divided by 8.
+/// When bloom.threshold > 0 a bright-pass is applied after filtering.
+@fragment
+fn fs_downsample(in: VertexOutput) -> @location(0) vec4<f32> {
+    let uv = in.uv;
+    let texel = 1.0 / vec2<f32>(textureDimensions(t_input));
+
+    let center = textureSample(t_input, s_input, uv).rgb;
+    let tl = textureSample(t_input, s_input, uv + vec2<f32>(-1.0, -1.0) * texel).rgb;
+    let tr = textureSample(t_input, s_input, uv + vec2<f32>( 1.0, -1.0) * texel).rgb;
+    let bl = textureSample(t_input, s_input, uv + vec2<f32>(-1.0,  1.0) * texel).rgb;
+    let br = textureSample(t_input, s_input, uv + vec2<f32>( 1.0,  1.0) * texel).rgb;
+
+    var color = (center * 4.0 + tl + tr + bl + br) / 8.0;
+
+    // Bright extraction on the first downsample level (threshold guard)
+    if bloom.threshold > 0.0 {
+        color = bright_extract(color, bloom.threshold, bloom.soft_threshold);
+    }
+
+    return vec4<f32>(color, 1.0);
+}
+
+// ── Upsample pass ─────────────────────────────────────────────────────────────
+
+/// 9-tap tent filter (3×3):
+///   corners × 1, axis-aligned edges × 2, centre × 4  →  /16
+@fragment
+fn fs_upsample(in: VertexOutput) -> @location(0) vec4<f32> {
+    let uv = in.uv;
+    let texel = 1.0 / vec2<f32>(textureDimensions(t_input));
+
+    let tl = textureSample(t_input, s_input, uv + vec2<f32>(-1.0, -1.0) * texel).rgb;
+    let tc = textureSample(t_input, s_input, uv + vec2<f32>( 0.0, -1.0) * texel).rgb;
+    let tr = textureSample(t_input, s_input, uv + vec2<f32>( 1.0, -1.0) * texel).rgb;
+    let ml = textureSample(t_input, s_input, uv + vec2<f32>(-1.0,  0.0) * texel).rgb;
+    let mc = textureSample(t_input, s_input, uv).rgb;
+    let mr = textureSample(t_input, s_input, uv + vec2<f32>( 1.0,  0.0) * texel).rgb;
+    let bl = textureSample(t_input, s_input, uv + vec2<f32>(-1.0,  1.0) * texel).rgb;
+    let bc = textureSample(t_input, s_input, uv + vec2<f32>( 0.0,  1.0) * texel).rgb;
+    let br = textureSample(t_input, s_input, uv + vec2<f32>( 1.0,  1.0) * texel).rgb;
+
+    // Tent weights: corners×1 + edges×2 + centre×4 → sum=16
+    let color = (tl + tr + bl + br
+               + (tc + ml + mr + bc) * 2.0
+               + mc * 4.0) / 16.0;
+
+    return vec4<f32>(color, 1.0);
+}

crates/voltex_renderer/src/tonemap_shader.wgsl

@@ -0,0 +1,68 @@
+// Tonemap pass shader.
+// Combines HDR scene colour + bloom, applies exposure and ACES tonemapping,
+// then converts to gamma-corrected sRGB for the swapchain.
+
+// ── Group 0 ───────────────────────────────────────────────────────────────────
+
+@group(0) @binding(0) var t_hdr:     texture_2d<f32>;
+@group(0) @binding(1) var t_bloom:   texture_2d<f32>;
+@group(0) @binding(2) var s_sampler: sampler;
+
+struct TonemapUniform {
+    bloom_intensity: f32,
+    exposure:        f32,
+    _padding:        vec2<f32>,
+};
+
+@group(0) @binding(3) var<uniform> tonemap: TonemapUniform;
+
+// ── Vertex stage ──────────────────────────────────────────────────────────────
+
+struct VertexInput {
+    @location(0) position: vec2<f32>,
+};
+
+struct VertexOutput {
+    @builtin(position) clip_position: vec4<f32>,
+    @location(0)       uv:            vec2<f32>,
+};
+
+@vertex
+fn vs_main(v: VertexInput) -> VertexOutput {
+    var out: VertexOutput;
+    out.clip_position = vec4<f32>(v.position, 0.0, 1.0);
+    out.uv = vec2<f32>(v.position.x * 0.5 + 0.5, 1.0 - (v.position.y * 0.5 + 0.5));
+    return out;
+}
+
+// ── ACES tonemap ──────────────────────────────────────────────────────────────
+
+fn aces_tonemap(x: vec3<f32>) -> vec3<f32> {
+    let num = x * (2.51 * x + vec3<f32>(0.03));
+    let den = x * (2.43 * x + vec3<f32>(0.59)) + vec3<f32>(0.14);
+    return clamp(num / den, vec3<f32>(0.0), vec3<f32>(1.0));
+}
+
+// ── Fragment stage ────────────────────────────────────────────────────────────
+
+@fragment
+fn fs_main(in: VertexOutput) -> @location(0) vec4<f32> {
+    let uv = in.uv;
+
+    let hdr   = textureSample(t_hdr,   s_sampler, uv).rgb;
+    let bloom = textureSample(t_bloom, s_sampler, uv).rgb;
+
+    // Combine HDR + bloom
+    var color = hdr + bloom * tonemap.bloom_intensity;
+
+    // Apply exposure
+    color = color * tonemap.exposure;
+
+    // ACES tonemapping
+    color = aces_tonemap(color);
+
+    // Gamma correction (linear → sRGB, γ = 2.2)
+    color = pow(color, vec3<f32>(1.0 / 2.2));
+
+    return vec4<f32>(color, 1.0);
+}