绘图线在SDL2 C ++中闪烁。如何修改我的游戏循环？

Question

我的线条图很好，但线条闪烁。我想改变循环的FPS，但我想我只需要在另一行中添加我的RenderPresent（）代码或添加一些新的代码来渲染该行。我尝试了很多可能性，没有任何效果。

我该怎么做才能阻止线条闪烁？如果您需要更多信息，请写评论。

// Global variables
SDL_Event event;             // Event object
int mouse_x = 0;             // Actual Mouse Coordinate X
int mouse_y = 0;             // Actual Mouse Coordinate Y
int mouse_last_x = 0;        // The coordinate X by last click
int mouse_last_y = 0;        // The coordinate Y by last click
bool dragged = false;        // Boolean after I clicked on some place
bool running = true;         // Makes the game loop run

void GameWin::loop()         //Game Loop
{
    while (running)
    {
        SDL_GetMouseState(&mouse_x, &mouse_y);  // Get Mouse Coordninates
        SDL_PollEvent(&event);

        SDL_SetRenderDrawColor(GameWin::renderer, 0, 0, 0, SDL_ALPHA_OPAQUE);  // Draw The Background Black

        update();
        render();  

        switch (event.type)
        {
        case SDL_QUIT:
            running = false;
            break;
        case SDL_MOUSEBUTTONDOWN:  // Mouse Click Event
            if (event.button.button == SDL_BUTTON_LEFT)
            {
                mouse_last_x = mouse_x; // After Left Click Save my Mouse Coordingates
                mouse_last_y = mouse_y;
                dragged = true;        
            }
            break;
        case SDL_MOUSEMOTION:
            if (dragged)
            {
                SDL_SetRenderDrawColor(GameWin::renderer, 137, 255, 85, SDL_ALPHA_OPAQUE); // Set The Color Line To Green
                SDL_RenderDrawLine(GameWin::renderer, mouse_last_x, mouse_last_y, mouse_x, mouse_y); // Draw The Line
                SDL_RenderPresent(GameWin::renderer); // Render Line
            }
            break;
        case SDL_MOUSEBUTTONUP:
            if (dragged)
            {
                dragged= false;
                mouse_last_x = mouse_x;
                mouse_last_y = mouse_y;
            }
            break;
        default:
            break;
        }
    }
}

// My render method 
void GameWin::render()
{
    SDL_RenderClear(GameWin::renderer);
    SDL_RenderPresent(GameWin::renderer);
}

Answer 1

首先，您不会检查是否发生任何事件。你调用SDL_PollEvent，然后处理事件 - 它可能没问题，或者它可能完全错误，因为不能保证队列中有事件。如果队列为空，SDL_PollEvent返回0 - 这意味着它没有用有意义的数据填充您的事件结构。

其次，不要将事件处理与绘图结合起来。获取迭代之间发生的所有事件，然后绘制一次。

基本上它应该是这样的：

#include "SDL.h"

// Global variables
SDL_Event event;             // Event object
int mouse_x = 0;             // Actual Mouse Coordinate X
int mouse_y = 0;             // Actual Mouse Coordinate Y
int mouse_last_x = 0;        // The coordinate X by last click
int mouse_last_y = 0;        // The coordinate Y by last click
bool dragged = false;        // Boolean after I clicked on some place
bool running = true;         // Makes the game loop run

int main(int argc, char **argv) {
    SDL_Init(SDL_INIT_VIDEO);
    SDL_Window *w = NULL;
    SDL_Renderer *renderer = NULL;
    SDL_CreateWindowAndRenderer(640, 480, 0, &w, &renderer);

    while (running)
    {
        SDL_SetRenderDrawColor(renderer, 0, 0, 0, SDL_ALPHA_OPAQUE);
        SDL_RenderClear(renderer);

        SDL_GetMouseState(&mouse_x, &mouse_y);  // Get Mouse Coordninates
        while(SDL_PollEvent(&event)) {
            switch (event.type)
            {
            case SDL_QUIT:
                running = false;
                break;
            case SDL_MOUSEBUTTONDOWN:  // Mouse Click Event
                if (event.button.button == SDL_BUTTON_LEFT)
                {
                    mouse_last_x = mouse_x; // After Left Click Save my Mouse Coordingates
                    mouse_last_y = mouse_y;
                    dragged = true;        
                }
                break;
            case SDL_MOUSEBUTTONUP:
                if (dragged)
                {
                    dragged= false;
                    mouse_last_x = mouse_x;
                    mouse_last_y = mouse_y;
                }
                break;
            default:
                break;
            }
        }

        if(!running) break;

        if (dragged)
        {
            SDL_SetRenderDrawColor(renderer, 137, 255, 85, SDL_ALPHA_OPAQUE); // Set The Color Line To Green
            SDL_RenderDrawLine(renderer, mouse_last_x, mouse_last_y, mouse_x, mouse_y); // Draw The Line
        }

        SDL_RenderPresent(renderer);
    }
}