feat: add SSAA

src/app.rs

@@ -52,6 +52,8 @@ pub struct FractalApp {
     color_scale: f32,
     color_offset: f32,
     palette: u32,
+    /// Supersample each pixel 2×2 for smoother edges (costs ~4× fragment work).
+    antialias: bool,
 
     /// Reference orbit (`Z_n` as f32 pairs) for the current view.
     reference: Arc<Vec<[f32; 2]>>,
@@ -107,6 +109,7 @@ impl FractalApp {
             color_scale: 0.15,
             color_offset: 0.0,
             palette: 0,
+            antialias: false,
             reference: Arc::new(Vec::new()),
             generation: 0,
             ref_center_re,
@@ -377,7 +380,7 @@ impl FractalApp {
             bailout_sq: BAILOUT_SQ,
             is_julia: matches!(self.mode, FractalMode::Julia) as u32,
             palette_id: self.palette,
-            _pad0: 0,
+            aa_level: if self.antialias { 2 } else { 1 },
             dc_offset: self.dc_offset(),
         }
     }
@@ -484,6 +487,8 @@ impl FractalApp {
                     ui.selectable_value(&mut self.palette, i as u32, *name);
                 }
             });
+        ui.checkbox(&mut self.antialias, "Antialiasing (2×2)")
+            .on_hover_text("Supersample each pixel for smoother edges (~4× slower).");
 
         ui.separator();
         let (cre, cim) = self.view.center_f64();

src/fractal/renderer.rs

@@ -30,7 +30,8 @@ pub struct Uniforms {
     /// 0 = Mandelbrot, 1 = Julia.
     pub is_julia: u32,
     pub palette_id: u32,
-    pub _pad0: u32,
+    /// Supersampling factor per axis: 1 = off, 2 = 2×2 (4 samples).
+    pub aa_level: u32,
     /// Complex offset of the view center from the reference center, so a stale
     /// or reused reference (computed at a slightly different center) still maps
     /// correctly. Added to every pixel's per-pixel offset.

src/shaders/mandelbrot.wgsl

@@ -21,7 +21,7 @@ struct Uniforms {
     bailout_sq: f32,
     is_julia: u32,
     palette_id: u32,
-    _pad0: u32,
+    aa_level: u32,
     dc_offset: vec2<f32>,
 };
 
@@ -74,12 +74,12 @@ fn palette(id: u32, t: f32) -> vec3<f32> {
     return a + b * cos(6.28318530718 * (c * t + d));
 }
 
-@fragment
-fn fs_main(in: VsOut) -> @location(0) vec4<f32> {
-    // Per-pixel offset. For Mandelbrot this is the c-plane offset added every
-    // step (delta starts at 0). For Julia it is the z-plane offset that seeds
-    // the initial delta (c is fixed, so nothing is added per step).
-    let offset = in.centered * u.span + u.dc_offset;
+// Perturbation iterate + color a single sample. `offset` is the per-pixel
+// offset in complex units. For Mandelbrot it is the c-plane offset added every
+// step (delta starts at 0); for Julia it is the z-plane offset that seeds the
+// initial delta (c is fixed, so nothing is added per step). Interior pixels
+// return black.
+fn shade(offset: vec2<f32>) -> vec3<f32> {
     let z0 = ref_orbit[0]; // reference start (0 for Mandelbrot, center for Julia)
 
     var step_add = offset;
@@ -130,7 +130,7 @@ fn fs_main(in: VsOut) -> @location(0) vec4<f32> {
     }
 
     if (!escaped) {
-        return vec4<f32>(0.0, 0.0, 0.0, 1.0); // interior of the set
+        return vec3<f32>(0.0, 0.0, 0.0); // interior of the set
     }
 
     // Continuous (smooth) iteration count.
@@ -142,5 +142,32 @@ fn fs_main(in: VsOut) -> @location(0) vec4<f32> {
     // varies smoothly instead of aliasing into speckle.
     let ci = sqrt(max(smooth_i, 0.0));
     let t = fract(ci * u.color_scale + u.color_offset);
-    return vec4<f32>(palette(u.palette_id, t), 1.0);
+    return palette(u.palette_id, t);
+}
+
+@fragment
+fn fs_main(in: VsOut) -> @location(0) vec4<f32> {
+    let base = in.centered * u.span + u.dc_offset;
+
+    let aa = max(u.aa_level, 1u);
+    if (aa <= 1u) {
+        return vec4<f32>(shade(base), 1.0);
+    }
+
+    // Screen-space complex-units-per-pixel, used to place sub-pixel samples.
+    // Derivatives must be evaluated in uniform control flow, so take them here.
+    let dx = dpdx(base);
+    let dy = dpdy(base);
+
+    var acc = vec3<f32>(0.0, 0.0, 0.0);
+    let inv = 1.0 / f32(aa);
+    for (var sy: u32 = 0u; sy < aa; sy = sy + 1u) {
+        for (var sx: u32 = 0u; sx < aa; sx = sx + 1u) {
+            // Sample centers evenly spread across the pixel, jitter in (-0.5, 0.5).
+            let jx = (f32(sx) + 0.5) * inv - 0.5;
+            let jy = (f32(sy) + 0.5) * inv - 0.5;
+            acc = acc + shade(base + jx * dx + jy * dy);
+        }
+    }
+    return vec4<f32>(acc / f32(aa * aa), 1.0);
 }