fixes

layout-engine/src/chart_layout.rs

@@ -129,10 +129,23 @@ pub struct LineChartLayout {
     pub show_labels: bool,
     pub label_font: f64,
     pub label_color: String,
+    pub smooth: bool,
     /// X axis line endpoints
     pub x_axis_y: f64,
     pub x_axis_x1: f64,
     pub x_axis_x2: f64,
+    /// Vertical reference lines
+    pub ref_lines: Vec<RefLineLayout>,
+}
+
+pub struct RefLineLayout {
+    pub x: f64,
+    pub y1: f64,
+    pub y2: f64,
+    pub color: String,
+    pub width: f64,
+    pub dash: bool,
+    pub label: Option<String>,
 }
 
 pub struct PieSlice {
@@ -223,6 +236,10 @@ pub trait ChartDataSource {
     fn inner_radius(&self) -> Option<f64>;
     fn show_points(&self) -> Option<bool>;
     fn line_width(&self) -> Option<f64>;
+    fn curve_type(&self) -> Option<&str>;
+    fn reference_lines(&self) -> &[dreport_core::models::ChartReferenceLine];
+    fn show_vertical_grid(&self) -> bool;
+    fn vertical_grid_color(&self) -> Option<&str>;
 }
 
 // ---------------------------------------------------------------------------
@@ -314,6 +331,18 @@ impl ChartDataSource for crate::data_resolve::ResolvedChartData {
     fn line_width(&self) -> Option<f64> {
         self.style.line_width
     }
+    fn curve_type(&self) -> Option<&str> {
+        self.style.curve_type.as_deref()
+    }
+    fn reference_lines(&self) -> &[dreport_core::models::ChartReferenceLine] {
+        self.axis.as_ref().map_or(&[], |a| &a.reference_lines)
+    }
+    fn show_vertical_grid(&self) -> bool {
+        self.axis.as_ref().and_then(|a| a.show_vertical_grid).unwrap_or(true)
+    }
+    fn vertical_grid_color(&self) -> Option<&str> {
+        self.axis.as_ref().and_then(|a| a.vertical_grid_color.as_deref())
+    }
 }
 
 // ---------------------------------------------------------------------------
@@ -403,6 +432,18 @@ impl ChartDataSource for crate::ChartRenderData {
     fn line_width(&self) -> Option<f64> {
         self.line_width
     }
+    fn curve_type(&self) -> Option<&str> {
+        self.curve_type.as_deref()
+    }
+    fn reference_lines(&self) -> &[dreport_core::models::ChartReferenceLine] {
+        &self.reference_lines
+    }
+    fn show_vertical_grid(&self) -> bool {
+        self.show_vertical_grid
+    }
+    fn vertical_grid_color(&self) -> Option<&str> {
+        self.vertical_grid_color.as_deref()
+    }
 }
 
 // ---------------------------------------------------------------------------
@@ -693,22 +734,14 @@ pub fn compute_x_labels_line(
             rotate_angle: 0.0,
         };
     }
-    let spacing = if n_cats == 1 {
-        pw
-    } else {
-        pw / (n_cats - 1) as f64
-    };
+    let step = pw / n_cats as f64;
     let max_label_len = categories.iter().map(|c| c.len()).max().unwrap_or(0);
-    let rotate_angle = compute_label_rotation(max_label_len, spacing);
+    let rotate_angle = compute_label_rotation(max_label_len, step);
     let labels = categories
         .iter()
         .enumerate()
         .map(|(ci, cat)| {
-            let x = if n_cats == 1 {
-                px + pw / 2.0
-            } else {
-                px + ci as f64 * pw / (n_cats - 1) as f64
-            };
+            let x = px + step / 2.0 + ci as f64 * step;
             XLabel {
                 text: cat.clone(),
                 x,
@@ -833,6 +866,11 @@ pub fn compute_line_layout(data: &dyn ChartDataSource, cl: &ChartLayout) -> Line
     let show_labels = data.show_labels();
     let label_font = data.label_font_size().unwrap_or(2.2);
     let label_color = data.label_color().unwrap_or("#333").to_string();
+    let smooth = data.curve_type() == Some("smooth");
+
+    // Slot-based positioning: each category gets a slot, point centered in slot
+    // This adds padding on left/right so first/last points don't touch axes
+    let step = if n_cats > 0 { pw / n_cats as f64 } else { pw };
 
     let series = (0..data.series_count())
         .map(|si| {
@@ -841,11 +879,7 @@ pub fn compute_line_layout(data: &dyn ChartDataSource, cl: &ChartLayout) -> Line
                 .iter()
                 .enumerate()
                 .map(|(ci, val)| {
-                    let x = if n_cats == 1 {
-                        px + pw / 2.0
-                    } else {
-                        px + ci as f64 * pw / (n_cats - 1) as f64
-                    };
+                    let x = px + step / 2.0 + ci as f64 * step;
                     let y = py + ph - ((val - min_val) / range) * ph;
                     LinePoint { x, y, value: *val }
                 })
@@ -859,6 +893,42 @@ pub fn compute_line_layout(data: &dyn ChartDataSource, cl: &ChartLayout) -> Line
 
     let x_labels = compute_x_labels_line(data.categories(), px, py + ph, pw);
 
+    // Vertical grid lines at each category
+    let vgrid_color = data.vertical_grid_color().unwrap_or("#E5E7EB").to_string();
+    let mut ref_lines: Vec<RefLineLayout> = if data.show_vertical_grid() {
+        (0..n_cats).map(|ci| {
+            let x = px + step / 2.0 + ci as f64 * step;
+            RefLineLayout {
+                x,
+                y1: py,
+                y2: py + ph,
+                color: vgrid_color.clone(),
+                width: 0.15,
+                dash: false,
+                label: None,
+            }
+        }).collect()
+    } else {
+        vec![]
+    };
+
+    // Explicit reference lines (overlay on top of grid)
+    for rl in data.reference_lines() {
+        if rl.category_index >= n_cats {
+            continue;
+        }
+        let x = px + step / 2.0 + rl.category_index as f64 * step;
+        ref_lines.push(RefLineLayout {
+            x,
+            y1: py,
+            y2: py + ph,
+            color: rl.color.clone().unwrap_or_else(|| "#9CA3AF".to_string()),
+            width: rl.width.unwrap_or(0.3),
+            dash: rl.dash.unwrap_or(true),
+            label: rl.label.clone(),
+        });
+    }
+
     LineChartLayout {
         min_val,
         max_val,
@@ -870,9 +940,11 @@ pub fn compute_line_layout(data: &dyn ChartDataSource, cl: &ChartLayout) -> Line
         show_labels,
         label_font,
         label_color,
+        smooth,
         x_axis_y: py + ph,
         x_axis_x1: px,
         x_axis_x2: px + pw,
+        ref_lines,
     }
 }
 

layout-engine/src/chart_render.rs

@@ -121,14 +121,13 @@ fn render_line(svg: &mut String, data: &ResolvedChartData, cl: &ChartLayout) {
     // Y axis
     render_y_axis_svg(svg, &ll.y_axis);
 
+    let mut label_texts = String::new();
+
     for series_layout in &ll.series {
         let color = color_at(&cl.palette, series_layout.color_idx);
-        let mut points = String::new();
         let mut point_circles = String::new();
 
         for pt in &series_layout.points {
-            write!(points, "{:.2},{:.2} ", pt.x, pt.y).unwrap();
-
             if ll.show_points {
                 write!(
                     point_circles,
@@ -139,19 +138,75 @@ fn render_line(svg: &mut String, data: &ResolvedChartData, cl: &ChartLayout) {
             }
 
             if ll.show_labels {
-                svg_text(svg, pt.x, pt.y - 1.5, ll.label_font, &ll.label_color, SvgAnchor::Middle, &format_value(pt.value));
+                svg_text(&mut label_texts, pt.x, pt.y - 1.5, ll.label_font, &ll.label_color, SvgAnchor::Middle, &format_value(pt.value));
             }
         }
 
-        write!(
-            svg,
-            r##"<polyline points="{}" fill="none" stroke="{}" stroke-width="{:.2}" stroke-linejoin="round" stroke-linecap="round"/>"##,
-            points.trim(), color, ll.line_width
-        )
-        .unwrap();
+        if ll.smooth && series_layout.points.len() >= 2 {
+            // Catmull-Rom → cubic bezier smooth curve
+            let pts = &series_layout.points;
+            let mut d = format!("M{:.2},{:.2}", pts[0].x, pts[0].y);
+            for i in 0..pts.len() - 1 {
+                let p0 = if i > 0 { &pts[i - 1] } else { &pts[i] };
+                let p1 = &pts[i];
+                let p2 = &pts[i + 1];
+                let p3 = if i + 2 < pts.len() { &pts[i + 2] } else { &pts[i + 1] };
+
+                let cp1x = p1.x + (p2.x - p0.x) / 6.0;
+                let cp1y = p1.y + (p2.y - p0.y) / 6.0;
+                let cp2x = p2.x - (p3.x - p1.x) / 6.0;
+                let cp2y = p2.y - (p3.y - p1.y) / 6.0;
+
+                write!(d, " C{:.2},{:.2} {:.2},{:.2} {:.2},{:.2}",
+                    cp1x, cp1y, cp2x, cp2y, p2.x, p2.y
+                ).unwrap();
+            }
+            write!(
+                svg,
+                r##"<path d="{}" fill="none" stroke="{}" stroke-width="{:.2}" stroke-linejoin="round" stroke-linecap="round"/>"##,
+                d, color, ll.line_width
+            )
+            .unwrap();
+        } else {
+            let mut points = String::new();
+            for pt in &series_layout.points {
+                write!(points, "{:.2},{:.2} ", pt.x, pt.y).unwrap();
+            }
+            write!(
+                svg,
+                r##"<polyline points="{}" fill="none" stroke="{}" stroke-width="{:.2}" stroke-linejoin="round" stroke-linecap="round"/>"##,
+                points.trim(), color, ll.line_width
+            )
+            .unwrap();
+        }
         svg.push_str(&point_circles);
     }
 
+    // Data labels (rendered after lines/points so they appear on top)
+    svg.push_str(&label_texts);
+
+    // Reference lines (vertical)
+    for rl in &ll.ref_lines {
+        if rl.dash {
+            write!(
+                svg,
+                r##"<line x1="{:.2}" y1="{:.2}" x2="{:.2}" y2="{:.2}" stroke="{}" stroke-width="{:.2}" stroke-dasharray="1.5,1"/>"##,
+                rl.x, rl.y1, rl.x, rl.y2, rl.color, rl.width
+            )
+            .unwrap();
+        } else {
+            write!(
+                svg,
+                r##"<line x1="{:.2}" y1="{:.2}" x2="{:.2}" y2="{:.2}" stroke="{}" stroke-width="{:.2}"/>"##,
+                rl.x, rl.y1, rl.x, rl.y2, rl.color, rl.width
+            )
+            .unwrap();
+        }
+        if let Some(ref label) = rl.label {
+            svg_text(svg, rl.x, rl.y1 - 1.0, 2.0, &rl.color, SvgAnchor::Middle, label);
+        }
+    }
+
     // X axis labels
     render_x_labels_svg(svg, &ll.x_labels);
 
@@ -560,6 +615,9 @@ mod tests {
             y_label: Some("Revenue".to_string()),
             show_grid: None,
             grid_color: None,
+            show_vertical_grid: None,
+            vertical_grid_color: None,
+            reference_lines: vec![],
         });
         let svg = render_svg(&data, 100.0, 60.0);
 
@@ -575,6 +633,9 @@ mod tests {
             y_label: Some("Y Label".to_string()),
             show_grid: None,
             grid_color: None,
+            show_vertical_grid: None,
+            vertical_grid_color: None,
+            reference_lines: vec![],
         });
         let svg = render_svg(&data, 80.0, 80.0);
 

layout-engine/src/lib.rs

@@ -161,8 +161,21 @@ pub struct ChartRenderData {
     // Title align
     #[serde(default)]
     pub title_align: Option<String>,
+    // Curve type for line charts
+    #[serde(default)]
+    pub curve_type: Option<String>,
+    // Vertical reference lines
+    #[serde(default)]
+    pub reference_lines: Vec<dreport_core::models::ChartReferenceLine>,
+    // Vertical grid
+    #[serde(default = "default_true")]
+    pub show_vertical_grid: bool,
+    #[serde(default)]
+    pub vertical_grid_color: Option<String>,
 }
 
+fn default_true() -> bool { true }
+
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct ChartSeriesData {
     pub name: String,
@@ -340,6 +353,10 @@ impl From<&data_resolve::ResolvedChartData> for ChartRenderData {
             legend_font_size: cd.legend.as_ref().and_then(|l| l.font_size),
             x_label: cd.axis.as_ref().and_then(|a| a.x_label.clone()),
             y_label: cd.axis.as_ref().and_then(|a| a.y_label.clone()),
+            curve_type: cd.style.curve_type.clone(),
+            reference_lines: cd.axis.as_ref().map_or_else(Vec::new, |a| a.reference_lines.clone()),
+            show_vertical_grid: cd.axis.as_ref().and_then(|a| a.show_vertical_grid).unwrap_or(true),
+            vertical_grid_color: cd.axis.as_ref().and_then(|a| a.vertical_grid_color.clone()),
         }
     }
 }

layout-engine/src/pdf_render.rs

@@ -1015,11 +1015,33 @@ fn render_chart(
                 }));
                 let path = {
                     let mut pb = PathBuilder::new();
-                    for (i, (lx, ly)) in points.iter().enumerate() {
-                        if i == 0 {
-                            pb.move_to(mm(*lx), mm(*ly));
-                        } else {
-                            pb.line_to(mm(*lx), mm(*ly));
+                    if ll.smooth && points.len() >= 2 {
+                        let pts = &series_layout.points;
+                        pb.move_to(mm(pts[0].x), mm(pts[0].y));
+                        for i in 0..pts.len() - 1 {
+                            let p0 = if i > 0 { &pts[i - 1] } else { &pts[i] };
+                            let p1 = &pts[i];
+                            let p2 = &pts[i + 1];
+                            let p3 = if i + 2 < pts.len() { &pts[i + 2] } else { &pts[i + 1] };
+
+                            let cp1x = p1.x + (p2.x - p0.x) / 6.0;
+                            let cp1y = p1.y + (p2.y - p0.y) / 6.0;
+                            let cp2x = p2.x - (p3.x - p1.x) / 6.0;
+                            let cp2y = p2.y - (p3.y - p1.y) / 6.0;
+
+                            pb.cubic_to(
+                                mm(cp1x), mm(cp1y),
+                                mm(cp2x), mm(cp2y),
+                                mm(p2.x), mm(p2.y),
+                            );
+                        }
+                    } else {
+                        for (i, (lx, ly)) in points.iter().enumerate() {
+                            if i == 0 {
+                                pb.move_to(mm(*lx), mm(*ly));
+                            } else {
+                                pb.line_to(mm(*lx), mm(*ly));
+                            }
                         }
                     }
                     pb.finish()
@@ -1055,6 +1077,32 @@ fn render_chart(
                     }
                 }
             }
+            // Reference lines (vertical)
+            for rl in &ll.ref_lines {
+                let rl_color = parse_color(&rl.color);
+                chart_line_seg(
+                    surface,
+                    rl.x,
+                    rl.y1,
+                    rl.x,
+                    rl.y2,
+                    rl_color,
+                    (rl.width * 2.5) as f32,
+                );
+                if let Some(ref label) = rl.label {
+                    chart_text(
+                        surface,
+                        rl.x,
+                        rl.y1 - 1.0,
+                        label,
+                        2.0,
+                        &rl.color,
+                        ChartTextAlign::Center,
+                        fonts,
+                        measurer,
+                    );
+                }
+            }
             render_chart_x_labels(surface, &ll.x_labels, fonts, measurer);
             let ac = parse_color("#9CA3AF");
             chart_line_seg(