# Coal Rendering Fix Report
## Problem
Visual artifact: `_@_@_@_@_@_` pattern appearing on the far right edge of the screen instead of rendering as part of the train.
## Root Cause
The coal car ASCII art was being rendered at incorrect X coordinates:
- **D51**: Coal was rendered at `x + D51_LENGTH (83)` instead of at `x`
- **C51**: Coal was rendered at `x + C51_LENGTH (95)` instead of at `x`
- **Logo**: Coal was rendered at `x + 20` and car at `x + 40` instead of at `x`
The coal car is a **vertical component of the train**, not a separate horizontal car that follows behind. It should be rendered at the same X position as the main engine body, but positioned below it vertically.
## Solution
Modified `src/render.rs` to render coal at the correct X coordinate:
### D51 Coal (Line 78)
```rust
// BEFORE:
add_line_to_frame(frame, x + D51_LENGTH as i32, y, line, terminal);
// AFTER:
add_line_to_frame(frame, x, y, line, terminal);
```
### C51 Coal (Line 119)
```rust
// BEFORE:
add_line_to_frame(frame, x + C51_LENGTH as i32, y, line, terminal);
// AFTER:
add_line_to_frame(frame, x, y, line, terminal);
```
### Logo Coal (Line 159)
```rust
// BEFORE:
add_line_to_frame(frame, x + 20, y, line, terminal);
// AFTER:
add_line_to_frame(frame, x, y, line, terminal);
```
### Logo Car (Line 167)
```rust
// BEFORE:
add_line_to_frame(frame, x + 40, y, line, terminal);
// AFTER:
add_line_to_frame(frame, x, y, line, terminal);
```
## Verification
- ✅ All 8 smoke integration tests pass
- ✅ Binary compiles with zero warnings
- ✅ All train modes (D51, C51, Logo) now render correctly
- ✅ Coal car no longer appears as artifact on far right
- ✅ Coal renders as part of train vertically stacked below engine
## Technical Details
**Train Structure (Vertical Stacking):**
```
Engine body (D51_STR) - 7 lines
Wheels (D51_WHL) - 3 lines
Coal load (D51_COAL) - 11 lines
```
All components render at the same X position (`x`), with different Y offsets:
```
coal_y_offset = D51_STR.len() + D51_WHL[pattern].len()
y = y_base + coal_y_offset + i
```
This creates a vertically-stacked locomotive with coal cargo, not a horizontal train with separate cars.