solitaire_engine/src/card_plugin.rs

@@ -63,6 +63,36 @@ pub const TABLEAU_FACEDOWN_FAN_FRAC: f32 = 0.14;
 // foundation piles bleeding through when a 2 sits on an Ace.
 pub const STACK_FAN_FRAC: f32 = 0.025;
 
+/// Per-card horizontal fan step for the Draw-Three waste, in logical pixels.
+///
+/// Derived from the actual tableau column spacing (`Tableau2.x − Tableau1.x`)
+/// rather than a fixed fraction of card width, so the fan scales with the
+/// platform's `H_GAP_DIVISOR` (desktop ≈ 1.25×cw spacing, Android ≈ 1.03×cw).
+/// Public so `input_plugin` can hit-test the fanned waste cards at the exact
+/// x-offsets the renderer uses; any drift makes a click on the top fanned card
+/// land on the card beneath it.
+pub fn waste_fan_step(layout: &Layout) -> f32 {
+    tableau_col_step(layout) * 0.224
+}
+
+/// Horizontal distance between adjacent tableau columns (`Tableau2.x −
+/// Tableau1.x`), in logical pixels. The face-down stock is rendered one column
+/// step left of the waste, and the Draw-Three waste fan ([`waste_fan_step`]) is
+/// a fraction of it. Public so hit-testing mirrors the renderer exactly.
+pub fn tableau_col_step(layout: &Layout) -> f32 {
+    let t1 = layout
+        .pile_positions
+        .get(&KlondikePile::Tableau(Tableau::Tableau1))
+        .copied()
+        .unwrap_or_default();
+    let t2 = layout
+        .pile_positions
+        .get(&KlondikePile::Tableau(Tableau::Tableau2))
+        .copied()
+        .unwrap_or_default();
+    (t2.x - t1.x).abs()
+}
+
 /// Font size as a fraction of card width.
 const FONT_SIZE_FRAC: f32 = 0.28;
 
@@ -908,34 +938,18 @@ fn card_positions(game: &GameState, layout: &Layout) -> Vec<((Card, bool), Vec2,
         (KlondikePile::Tableau(Tableau::Tableau7), false),
     ];
 
-    // Compute the Draw-Three waste fan step proportional to the column spacing
-    // (waste_x − stock_x = card_width + h_gap) rather than a fixed fraction of
-    // card_width.  On desktop (H_GAP_DIVISOR=4) col_step = 1.25×cw and
-    // 0.224 × 1.25 = 0.28 — identical to the previous constant.  On Android
-    // (H_GAP_DIVISOR=32) col_step ≈ 1.031×cw so fan_step ≈ 0.231×cw, keeping
-    // the top fanned card's centre within the waste column's own horizontal
-    // footprint instead of spilling into the adjacent gap.
-    let tableau_col_step = {
-        let t1 = layout
-            .pile_positions
-            .get(&KlondikePile::Tableau(Tableau::Tableau1))
-            .copied()
-            .unwrap_or_default();
-        let t2 = layout
-            .pile_positions
-            .get(&KlondikePile::Tableau(Tableau::Tableau2))
-            .copied()
-            .unwrap_or_default();
-        (t2.x - t1.x).abs()
-    };
-    let waste_fan_step = tableau_col_step * 0.224;
+    // Draw-Three waste fan step, proportional to the column spacing so it scales
+    // with the platform's H_GAP_DIVISOR. Shared with input_plugin's hit-test via
+    // `waste_fan_step` so the two never drift (a drift puts the top fanned card's
+    // click target on the card beneath it).
+    let waste_fan_step = waste_fan_step(layout);
 
     for (pile_type, is_stock_area) in piles {
         let Some(mut base) = layout.pile_positions.get(&pile_type).copied() else {
             continue;
         };
         if matches!(pile_type, KlondikePile::Stock) && is_stock_area {
-            base.x -= tableau_col_step;
+            base.x -= tableau_col_step(layout);
         }
         let is_tableau = matches!(pile_type, KlondikePile::Tableau(_));
         let is_waste = matches!(pile_type, KlondikePile::Stock) && !is_stock_area;

solitaire_engine/src/input_plugin.rs

@@ -35,7 +35,7 @@ use crate::auto_complete_plugin::AutoCompleteState;
 use crate::card_animation::tuning::AnimationTuning;
 use crate::card_animation::{CardAnimation, MotionCurve};
 use crate::card_plugin::{
-    CardEntity, CardEntityIndex, HintHighlight, HintHighlightTimer, STACK_FAN_FRAC,
+    CardEntity, CardEntityIndex, HintHighlight, HintHighlightTimer, STACK_FAN_FRAC, waste_fan_step,
 };
 use crate::challenge_plugin::CHALLENGE_UNLOCK_LEVEL;
 use crate::events::{
@@ -1175,12 +1175,15 @@ fn card_position(
         Vec2::new(base.x, base.y + y_offset)
     } else if matches!(pile, KlondikePile::Stock) && game.draw_mode() == DrawStockConfig::DrawThree {
         // In Draw-Three mode the top 3 waste cards are fanned in X to match
-        // card_plugin::card_positions(). Hit-testing must use the same offsets
-        // so clicking the visually rightmost (top) card actually registers.
+        // card_plugin::card_positions(). Hit-testing uses the same `waste_fan_step`
+        // so clicking the visually rightmost (top) card actually registers — a
+        // fixed `card_size.x * 0.28` matched the renderer on desktop but drifted
+        // on Android (tighter column spacing), shifting the top card's hit target
+        // onto the card beneath it.
         let pile_len = game.waste_cards().len();
         let visible_start = pile_len.saturating_sub(3);
         let slot = stack_index.saturating_sub(visible_start) as f32;
-        Vec2::new(base.x + slot * layout.card_size.x * 0.28, base.y)
+        Vec2::new(base.x + slot * waste_fan_step(layout), base.y)
     } else {
         base
     }
@@ -1948,6 +1951,52 @@ mod tests {
         assert_eq!(result.2, vec![card]);
     }
 
+    #[test]
+    fn draw_three_waste_hit_test_matches_render_fan_step() {
+        // Regression: the Draw-Three waste hit-test must use the same fan step as
+        // the renderer (`card_plugin::waste_fan_step`). The previous hard-coded
+        // `card_size.x * 0.28` matched the renderer only on desktop (column step =
+        // 1.25*cw); under tighter Android-style spacing the two drift and the top
+        // fanned card's click target lands on the card beneath it — so dragging
+        // the visible top card plays the wrong one.
+        let mut game = GameState::new(7, DrawStockConfig::DrawThree);
+        let mut layout = compute_layout(Vec2::new(1280.0, 800.0), 0.0, 0.0, true);
+
+        // Force tight (Android-like) column spacing: ~1.03 * card_width.
+        let cw = layout.card_size.x;
+        let base = layout.pile_positions[&KlondikePile::Stock];
+        let t1 = layout.pile_positions[&KlondikePile::Tableau(Tableau::Tableau1)];
+        layout.pile_positions.insert(
+            KlondikePile::Tableau(Tableau::Tableau2),
+            Vec2::new(t1.x + cw * 1.03, t1.y),
+        );
+
+        clear_test_piles(&mut game);
+        let waste = vec![
+            Card::new(Deck::Deck1, Suit::Clubs, Rank::Two),
+            Card::new(Deck::Deck1, Suit::Hearts, Rank::Five),
+            Card::new(Deck::Deck1, Suit::Spades, Rank::Nine),
+            Card::new(Deck::Deck1, Suit::Diamonds, Rank::King),
+        ];
+        game.set_test_waste_cards(waste.clone());
+
+        // visible_start = len-3 = 1, so the top card sits at fan slot 2.
+        let top_index = waste.len() - 1;
+        let pos = card_position(&game, &layout, &KlondikePile::Stock, top_index);
+
+        let expected = base.x + 2.0 * waste_fan_step(&layout);
+        assert!(
+            (pos.x - expected).abs() < 1e-3,
+            "hit-test must use the shared waste fan step"
+        );
+        // The old fixed constant would have drifted from the renderer here.
+        let old = base.x + 2.0 * cw * 0.28;
+        assert!(
+            (pos.x - old).abs() > 1.0,
+            "shared step must differ from the old fixed step under tight spacing"
+        );
+    }
+
     #[test]
     fn find_draggable_skips_face_down_cards() {
         let game = GameState::new(42, DrawStockConfig::DrawOne);