如何在sdl2中渲染一个点

Question

我正在尝试使用 SDL 渲染一个点，但似乎无法获取要渲染的点。我在代码中没有收到任何错误，并且正在编译，但是窗口上没有出现任何内容。

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。任何建议都将受到赞赏，并且非常感谢帮助。

Answer 1

你错过了几件事。第一个也是最重要的是您的渲染器未初始化，这是通过SDL_CreateRenderer完成的。现在我们准备在窗口上绘图了。为此，您需要在渲染器上设置一种颜色（此颜色用于 RenderDrawPoint 和 RenderDrawLine 等函数）。

画出你的观点后，我们将把颜色设置为之前的颜色。我选择黑色作为背景，白色作为点的颜色，你可以选择任何你需要的，渲染器中设置颜色的函数是SDL_SetRenderDrawColor。

现在我们可以绘制了，但是在每次绘制之前，您必须清除屏幕，对渲染器进行所有绘制调用，然后显示您绘制的内容。

这是一个完整的示例，其中包含您所缺少的注释部分，我还将您的drawPoint移到了主循环中，因为最终这就是您可能想要的位置。

但是（非常罕见的使用）如果您想绘制一次并且不再更改屏幕上的内容，那么您可以将其带到墙外，调用clear并呈现一次并完成它。

#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();

}