feat: add cyclic color and speed options for brush settings

hcie-iced-app/crates/hcie-iced-gui/src/app.rs

@@ -587,6 +587,10 @@ pub struct ToolState {
     pub brush_color_variant: bool,
     /// Magnitude of the per-dab color variation (0.0..1.0).
     pub brush_variant_amount: f32,
+    /// True when the brush color should cycle through the hue over stroke distance.
+    pub brush_cyclic_color: bool,
+    /// Speed of the hue cycle along the stroke (0.01..5.0).
+    pub brush_cyclic_speed: f32,
     /// Timestamp of the last update() call for frame timing.
     pub last_update_instant: std::time::Instant,
     /// Imported brush presets from ABR/KPP files.
@@ -621,6 +625,8 @@ impl Default for ToolState {
             brush_spacing: 1.0,
             brush_color_variant: false,
             brush_variant_amount: 0.0,
+            brush_cyclic_color: false,
+            brush_cyclic_speed: 0.5,
             last_update_instant: std::time::Instant::now(),
             imported_brushes: Vec::new(),
             active_brush_preset: None,
@@ -778,6 +784,8 @@ pub enum Message {
     BrushSpacingChanged(f32),
     BrushColorVariantToggled(bool),
     BrushVariantAmountChanged(f32),
+    BrushCyclicColorToggled(bool),
+    BrushCyclicSpeedChanged(f32),
     BrushImportAbr,
     BrushImportAbrFile(Result<Vec<hcie_engine_api::BrushPreset>, String>),
     ResetToolDefaults,
@@ -1319,6 +1327,7 @@ fn build_brush_tip(state: &ToolState) -> BrushTip {
     }
 }
 
+
 /// Converts an imported/default brush-engine preset tip into the protocol tip used by `Engine`.
 ///
 /// **Arguments:** `source` is the preset-owned brush-engine tip. **Returns:** A protocol tip with
@@ -2564,7 +2573,7 @@ impl HcieIcedApp {
     /// Apply brush parameters from tool state to the engine.
     ///
     /// Called before starting a stroke to ensure the engine uses
-    /// the current brush size, opacity, hardness, and style.
+    /// the current brush size, opacity, hardness, style, and cyclic color.
     fn apply_brush_params(&mut self) {
         let mut tip = self
             .tool_state
@@ -2577,6 +2586,15 @@ impl HcieIcedApp {
         tip.opacity = self.tool_state.brush_opacity;
         tip.hardness = self.tool_state.brush_hardness;
         tip.spacing = self.tool_state.brush_spacing;
+        // Cyclic color is handled by engine state, not the tip, but preview rendering
+        // also reads the tip's time dynamics. Synchronize both here.
+        tip.time_enabled = self.tool_state.brush_cyclic_color;
+        tip.time_size_start = 1.0;
+        tip.time_size_end = 1.0;
+        tip.time_opacity_start = 1.0;
+        tip.time_opacity_end = 1.0;
+        tip.time_angle_start = 0.0;
+        tip.time_angle_end = 0.0;
         match self.tool_state.active_tool {
             Tool::Pen => {
                 tip.style = BrushStyle::Round;
@@ -2592,7 +2610,10 @@ impl HcieIcedApp {
             }
             _ => {}
         }
-        self.documents[self.active_doc].engine.set_brush_tip(tip);
+        let engine = &mut self.documents[self.active_doc].engine;
+        engine.set_brush_tip(tip);
+        engine.set_cyclic_color(self.tool_state.brush_cyclic_color);
+        engine.set_cyclic_speed(self.tool_state.brush_cyclic_speed);
     }
 
     /// Push the current SVG editor model into the active vector shape so the
@@ -4955,6 +4976,22 @@ impl HcieIcedApp {
                 self.settings.update_from_tool_state(&self.tool_state);
                 let _ = self.settings.save();
             }
+            Message::BrushCyclicColorToggled(enabled) => {
+                self.tool_state.brush_cyclic_color = enabled;
+                self.documents[self.active_doc]
+                    .engine
+                    .set_cyclic_color(enabled);
+                self.settings.update_from_tool_state(&self.tool_state);
+                let _ = self.settings.save();
+            }
+            Message::BrushCyclicSpeedChanged(speed) => {
+                self.tool_state.brush_cyclic_speed = speed;
+                self.documents[self.active_doc]
+                    .engine
+                    .set_cyclic_speed(speed);
+                self.settings.update_from_tool_state(&self.tool_state);
+                let _ = self.settings.save();
+            }
             Message::SelectionToleranceChanged(tol) => {
                 self.settings.tool_settings.magic_wand_tolerance = tol as f32;
                 self.settings.tool_settings.flood_fill_tolerance = tol as f32;