c++ - 如何在sdl2中渲染一个点

Question

我正在尝试使用 SDL 渲染一个点，但我似乎无法获得要渲染的点。我在代码中没有收到任何错误，它正在编译，但是窗口上没有显示任何内容。

代码:

   #include <iostream>
#include <SDL2/SDL.h>

using namespace std;

int main() {
    const int windowHeight = 600;
    const int windowWidth = 800;

    if (SDL_Init(SDL_INIT_VIDEO) < 0) {
        return 1;
        cout << "Initialization failed" << endl;
    }

    SDL_Window *window = SDL_CreateWindow("Practice making sdl Window",
            SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, windowWidth,
            windowHeight, SDL_WINDOW_SHOWN);

    if (window == NULL) {
        SDL_Quit();
        return 2;
    }
    SDL_Renderer *s;
    const int pointLocationx = windowWidth/2;
    const int pointLocationy = windowHeight/2;
    SDL_RenderDrawPoint(s, pointLocationx, pointLocationy);

    bool quit = false;
    SDL_Event event;
    while (!quit) {
        //drawing particles
        //setting up objects
        //repeated over and over again

        while (SDL_PollEvent(&event)) {
            if (event.type == SDL_QUIT) {
                quit = true;
            }
        }
    }

    SDL_DestroyWindow(window);
    SDL_Quit();

}

上面是我的代码。感谢任何建议，并非常感谢您的帮助。

Answer 1

您遗漏了几件事。第一个也是最重要的是你的渲染器没有初始化，这是用 SDL_CreateRenderer 完成的。 . 现在我们准备好在窗口上绘制了。为此，您需要在渲染器上设置颜色(此颜色用于 RenderDrawPoint 和 RenderDrawLine 等函数)。

绘制您的观点后，我们会将颜色设置为之前的颜色。我选择了黑色作为背景，白色作为点的颜色，你可以选择任何你需要的，在渲染器中设置颜色的函数是SDL_SetRenderDrawColor。 .

现在我们可以抽奖了，但是在每次抽奖之前你必须clear你的屏幕，对渲染器进行所有绘制调用，然后 show你画了什么。

这是一个完整的示例，其中包含关于您所遗漏内容的注释部分，我还将您的 drawPoint 移到了您的主循环中，因为在一天结束时您可能希望它位于何处。

但是(很少使用)如果你想画一次就再也不改变屏幕上的内容，那么你可以把它带到墙外，调用一次 clear 和 present 就可以了。

#include <iostream>
#include <SDL2/SDL.h>

using namespace std;

int main() {
    const int windowHeight = 600;
    const int windowWidth = 800;

    if (SDL_Init(SDL_INIT_VIDEO) < 0) {
        return 1;
        cout << "Initialization failed" << endl;
    }

    SDL_Window *window = SDL_CreateWindow("Practice making sdl Window",
            SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, windowWidth,
            windowHeight, SDL_WINDOW_SHOWN);

    if (window == NULL) {
        SDL_Quit();
        return 2;
    }

    // We create a renderer with hardware acceleration, we also present according with the vertical sync refresh.
    SDL_Renderer *s = SDL_CreateRenderer(window, 0, SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC) ;

    const int pointLocationx = windowWidth/2;
    const int pointLocationy = windowHeight/2;

    bool quit = false;
    SDL_Event event;

    while (!quit) {
        //drawing particles
        //setting up objects
        //repeated over and over again

        while (SDL_PollEvent(&event)) {
            if (event.type == SDL_QUIT) {
                quit = true;
            }
        }

        // We clear what we draw before
        SDL_RenderClear(s);
        // Set our color for the draw functions
        SDL_SetRenderDrawColor(s, 0xFF, 0xFF, 0xFF, 0xFF);
        // Now we can draw our point
        SDL_RenderDrawPoint(s, pointLocationx, pointLocationy);
        // Set the color to what was before
        SDL_SetRenderDrawColor(s, 0x00, 0x00, 0x00, 0xFF);
        // .. you could do some other drawing here
        // And now we present everything we draw after the clear.
        SDL_RenderPresent(s);
    }

    SDL_DestroyWindow(window);
    // We have to destroy the renderer, same as with the window.
    SDL_DestroyRenderer(s);
    SDL_Quit();

}