Out-of-Window Selection Rectangle

1#include <SDL.h>
2#include <iostream>
3
4class SelectionRectangle {
5public:
6  SelectionRectangle() : isSelecting{false} {}
7
8  void HandleMouseDown(
9    const SDL_MouseButtonEvent& event) {
10    if (event.button == SDL_BUTTON_LEFT) {
11      startX = event.x;
12      startY = event.y;
13      currentX = event.x;
14      currentY = event.y;
15      isSelecting = true;
16
17      // Enable mouse capture for out-of-window
18      // tracking
19      SDL_CaptureMouse(SDL_TRUE); 
20    }
21  }
22
23  void HandleMouseUp(
24    const SDL_MouseButtonEvent& event) {
25    if (event.button == SDL_BUTTON_LEFT) {
26      isSelecting = false;
27      SDL_CaptureMouse(SDL_FALSE);
28
29      // Calculate final selection area
30      int width = std::abs(currentX - startX);
31      int height = std::abs(currentY - startY);
32      std::cout << "Final selection: " << width
33        << "x" << height << " pixels\n";
34    }
35  }
36
37  void HandleMouseMotion(
38    const SDL_MouseMotionEvent& event) {
39    if (isSelecting) {
40      currentX = event.x;
41      currentY = event.y;
42    }
43  }
44
45  void Render(SDL_Renderer* renderer) {
46    if (isSelecting) {
47      // Calculate rectangle dimensions
48      int x = std::min(startX, currentX);
49      int y = std::min(startY, currentY);
50      int w = std::abs(currentX - startX);
51      int h = std::abs(currentY - startY);
52
53      // Draw selection rectangle
54      SDL_SetRenderDrawColor(
55        renderer, 0, 120, 255, 255);
56      SDL_Rect selectionRect{x, y, w, h};
57      SDL_RenderDrawRect(renderer,
58                         &selectionRect);
59
60      // Draw semi-transparent fill
61      SDL_SetRenderDrawColor(
62        renderer, 0, 120, 255, 64);
63      SDL_SetRenderDrawBlendMode(
64        renderer, SDL_BLENDMODE_BLEND);
65      SDL_RenderFillRect(renderer,
66                         &selectionRect);
67    }
68  }
69
70  bool IsSelecting() const {
71    return isSelecting;
72  }
73
74private:
75  bool isSelecting;
76  int startX, startY;
77  int currentX, currentY;
78};
79
80int main(int argc, char** argv) {
81  SDL_Init(SDL_INIT_VIDEO);
82  SDL_Window* window =
83    SDL_CreateWindow("Selection Rectangle",
84                     SDL_WINDOWPOS_CENTERED,
85                     SDL_WINDOWPOS_CENTERED,
86                     800, 600,
87                     SDL_WINDOW_SHOWN);
88  SDL_Renderer* renderer =
89    SDL_CreateRenderer(window, -1,
90                       SDL_RENDERER_ACCELERATED);
91
92  SelectionRectangle selection;
93  bool running = true;
94
95  while (running) {
96    SDL_Event event;
97    while (SDL_PollEvent(&event)) {
98      if (event.type ==
99        SDL_QUIT) { running = false; } else if (
100        event.type == SDL_MOUSEBUTTONDOWN) {
101        selection.HandleMouseDown(event.button);
102      } else if (event.type ==
103        SDL_MOUSEBUTTONUP) {
104        selection.HandleMouseUp(event.button);
105      } else if (event.type ==
106        SDL_MOUSEMOTION) {
107        selection.HandleMouseMotion(
108          event.motion);
109      }
110    }
111
112    // Clear and render
113    SDL_SetRenderDrawColor(renderer, 255, 255,
114                           255, 255);
115    SDL_RenderClear(renderer);
116    selection.Render(renderer);
117    SDL_RenderPresent(renderer);
118  }
119
120  SDL_DestroyRenderer(renderer);
121  SDL_DestroyWindow(window);
122  SDL_Quit();
123  return 0;
124}