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docs/superpowers/plans/2026-05-09-bouncing-hello-world-ball.md

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+# Bouncing "Hello World" Ball Implementation Plan
+
+> **For agentic workers:** REQUIRED SUB-SKILL: Use superpowers:subagent-driven-development (recommended) or superpowers:executing-plans to implement this plan task-by-task. Steps use checkbox (`- [ ]`) syntax for tracking.
+
+**Goal:** Modify `src/main.cpp` so that "Hello World" bounces around the screen inside a filled circle that changes colour on each wall hit.
+
+**Architecture:** Single-file firmware sketch. The ball position/velocity/colour are tracked in a `Ball` struct. Each `loop()` iteration clears the screen, updates position, bounces off edges (changing colour), and draws a filled circle with centred white text.
+
+**Tech Stack:** Arduino (PlatformIO), M5Unified, M5StickC Plus2 (ESP32), 135×240 TFT display.
+
+---
+
+### Task 1: Rewrite `src/main.cpp` with ball + text rendering
+
+**Files:**
+- Modify: `src/main.cpp` (entire file)
+
+- [ ] **Step 1: Replace the file content**
+
+Replace `src/main.cpp` with the following:
+
+```cpp
+#include <M5Unified.h>
+
+struct Ball {
+    float x, y;
+    float vx, vy;
+    uint16_t radius;
+    uint16_t color;
+};
+
+uint16_t colors[] = {TFT_RED, TFT_GREEN, TFT_BLUE, TFT_YELLOW, TFT_MAGENTA, TFT_CYAN};
+const int numColors = sizeof(colors) / sizeof(colors[0]);
+int colorIndex = 0;
+
+Ball ball;
+
+void setup() {
+    M5.begin();
+
+    ball.radius = 35;
+    ball.x = M5.Lcd.width() / 2.0f;
+    ball.y = M5.Lcd.height() / 2.0f;
+    ball.vx = 2.0f;
+    ball.vy = 2.5f;
+    ball.color = colors[0];
+}
+
+void loop() {
+    M5.Lcd.fillScreen(TFT_BLACK);
+
+    ball.x += ball.vx;
+    ball.y += ball.vy;
+
+    if (ball.x + ball.radius >= M5.Lcd.width() || ball.x - ball.radius <= 0) {
+        ball.vx *= -1;
+        colorIndex = (colorIndex + 1) % numColors;
+        ball.color = colors[colorIndex];
+        ball.x = (ball.x + ball.radius > M5.Lcd.width()) ? M5.Lcd.width() - ball.radius : ball.radius;
+    }
+
+    if (ball.y + ball.radius >= M5.Lcd.height() || ball.y - ball.radius <= 0) {
+        ball.vy *= -1;
+        colorIndex = (colorIndex + 1) % numColors;
+        ball.color = colors[colorIndex];
+        ball.y = (ball.y + ball.radius > M5.Lcd.height()) ? M5.Lcd.height() - ball.radius : ball.radius;
+    }
+
+    M5.Lcd.fillCircle((int)ball.x, (int)ball.y, ball.radius, ball.color);
+    M5.Lcd.setTextColor(TFT_WHITE);
+    M5.Lcd.setTextSize(1);
+    int16_t textW = M5.Lcd.textWidth("Hello World");
+    int16_t textH = 8;
+    M5.Lcd.setCursor((int)ball.x - textW / 2, (int)ball.y - textH / 2);
+    M5.Lcd.print("Hello World");
+
+    delay(15);
+}
+```
+
+- [ ] **Step 2: Verify the file was written correctly**
+
+Run: `cat src/main.cpp | head -5`
+Expected: file starts with `#include <M5Unified.h>`
+
+Also check that `#include <vector>` is removed (no longer needed).
+
+- [ ] **Step 3: Commit**
+
+```bash
+git add src/main.cpp
+git commit -m "feat: bouncing Hello World ball that changes colour on edge hit"
+```