C++ sdl基于鼠标位置绘制动态矩形

Question

对许多人来说，这看起来很明显，但我被卡住了，我找不到任何帮助我的教程，因此在这里找到答案会很好。

我试图制作一个矩形，就像你在RTS游戏中所做的那样，可以说是一个动态选择框，但它不能正常工作。 这也将是足够的人列出了要点这对于创建像一个盒子的每一步该

（不要怀疑我真的很新的C++）

Mouse.h：

#ifndef MOUSE_H_ 
#define MOUSE_H_ 

class Mouse { 

public: 
    bool leftButtonDown = false; 
    bool mouseMoves = false; 

    struct MouseCoords { 
     int x = -1; 
     int y = -1; 
    }; 

    MouseCoords start_coords; 
    MouseCoords move_coords; 
    Mouse(){} 

    void setState(Uint32 eventType, SDL_Event event){ 

     if (eventType == SDL_MOUSEBUTTONDOWN) { 
      this->leftButtonDown = true; 
      SDL_GetMouseState(&this->start_coords.x, &this->start_coords.y); 
     } 

     if (eventType == SDL_MOUSEBUTTONUP) { 
      this->leftButtonDown = false; 
     } 

     if (eventType == SDL_MOUSEMOTION) { 
      this->mouseMoves = true; 
      this->move_coords.x = event.motion.x; 
      this->move_coords.y = event.motion.y; 
     } else { 
      this->mouseMoves = false; 
     } 
    } 

    /** 
    * Provides coordinates when mousebutton down 
    */ 
    MouseCoords getCoordinates(){ 
     return move_coords; 
    } 

    /** 
    * Refresh the coordinates. MUST be called after Mouse::clearCoordinates(); 
    */ 
    void clearCoordinates(){ 
     this->move_coords.x = -1; 
     this->move_coords.y = -1; 

    } 

    /** 
    * Creates selector rect, call this in the render loop 
    */ 
    void createSelectBox(SDL_Renderer *renderer){ 
     if(this->leftButtonDown) { 
      Block rect(
         this->start_coords.x, 
         this->move_coords.y, 
         this->start_coords.y -this->move_coords.y , 
         this->move_coords.x - this->start_coords.x 
         ); 
      rect.draw(renderer); 
      this->clearCoordinates(); 
     } 
    } 
}; 

#endif 

Block.h

#ifndef BLOCK_H_ 
#define BLOCK_H_ 
/** 
* Standard Class which can be used to build a player, enemy, or something similar 
*/ 

class Block{ 
    SDL_Rect rect; 
public: 
    Block(int x=10, int y=10, int w=10, int h=10, int filled=true){ 
     rect.x = x; 
     rect.y = y; 
     rect.w = w; 
     rect.h = h; 
    } 

    /** 
    * draw with the given rendererer 
    */ 
    void draw(SDL_Renderer *renderer){ 
     SDL_SetRenderDrawColor(renderer , 200 , 155 , 255 , 255); 
     SDL_RenderDrawRect(renderer, &rect); 
     SDL_RenderPresent(renderer); 
    } 

    bool framed(){ 
     return 0; 
    } 

}; 
#endif 

然后在我的main.cpp

SDL_Window *window; 
SDL_Renderer *renderer; 
Mouse mouse; 
Block rect; 


void renderWindow(){ 
    window = SDL_CreateWindow("commanding rects", 100, 100, 700, 600, 0); 
    renderer = SDL_CreateRenderer(window, -1, 0); 
} 

void renderGame(Mouse mouse){ 
    SDL_RenderSetLogicalSize(renderer, 400, 300); 
    SDL_SetRenderDrawColor(renderer, 0, 0, 0, 0); 
    SDL_RenderClear(renderer); 
    SDL_RenderPresent(renderer); 
    mouse.createSelectBox(renderer); 

} 


void gameLoop(){ 
    bool game_run = true; 
    while (game_run) { 
     SDL_Event event; 
     while(SDL_PollEvent(&event)){ 
      if (event.type == SDL_QUIT) { 
       game_run = false; 
      } 
      mouse.setState(event.type, event); 
     } 
     renderGame(mouse); 
     SDL_Delay(15); 
    } 

} 


int main(){ 
    renderWindow(); 
    gameLoop(); 
    return 0; 
} 

Answer 1

我终于发现我做错了什么。

我正在检索绘制矩形的错误起点。 当触发鼠标按下我得的event.button.x代替GetMouseState

这里是更新Mouse.h

#ifndef MOUSE_H_ 
#define MOUSE_H_ 

class Mouse { 

public: 
    bool leftButtonDown = false; 
    bool mouseMoves = false; 

    struct MouseCoords { 
     int x = -1; 
     int y = -1; 
    }; 

    MouseCoords start_coords; 
    MouseCoords move_coords; 
    Mouse(){} 

    void setState(Uint32 eventType, SDL_Event event){ 

     if (eventType == SDL_MOUSEBUTTONDOWN) { 
      this->leftButtonDown = true; 
      this->start_coords.x = event.button.x; 
      this->start_coords.y = event.button.y; 
     } 

     if (eventType == SDL_MOUSEBUTTONUP) { 
      this->leftButtonDown = false; 
     } 

     if (eventType == SDL_MOUSEMOTION) { 
      this->move_coords.x = event.motion.x; 
      this->move_coords.y = event.motion.y; 
     } 
    } 

    /** 
    * Provides coordinates when mousebutton down 
    */ 
    MouseCoords getCoordinates(){ 
     return move_coords; 
    } 


    /** 
    * Creates selector rect, call this in the render loop 
    */ 
    void createSelectBox(SDL_Renderer *renderer){ 

     if(this->leftButtonDown) { 

      float width = this->move_coords.x - this->start_coords.x; 
      float height = this->start_coords.y - this->move_coords.y; 
      float x = this->start_coords.x ; 
      float y = this->move_coords.y; 

      Block rect(x, y,width, height); 
      rect.draw(renderer); 



     } 


    } 
}; 

#endif 

Answer 2

我在这里发现了一个问题：

void createSelectBox(SDL_Renderer *renderer){ 
    if(this->leftButtonDown) { 
     Block rect(this->mousedown_coords.x, 
        this->mousemove_coords.y, 
        this->mousedown_coords.y - this->mousemove_coords.y, 
        this->mousemove_coords.x - this->mousedown_coords.x); 

在这一段代码，你矩形的宽度和高度，不管是什么鼠标坐标的值都设置为0。由于您正在绘制边界框，因此我想您需要存储两组x，y坐标，一个用于按下鼠标按钮，另一个用于释放时。