c++ - 如何使用 SDL_CreateTexture

Question

我想知道如何使用SDL_CreateTexture功能。
我只想创建纹理，给它一种颜色并将其绘制在屏幕上的某个位置。我不想加载任何图片。
我以为我可以按此顺序使用 SDL_CreateTexture、SDL_SetTextureColorMod、SDL_RenderCopy、SDL_RenderPresent，但我总是得到一个黑色矩形而不是红色矩形。

#include <SDL.h>

int main(int argc, char* argv[]) {

    SDL_Init(SDL_INIT_EVERYTHING);

    SDL_Window *MainWindow = SDL_CreateWindow("My Game Window",
                                  SDL_WINDOWPOS_CENTERED,
                                  SDL_WINDOWPOS_CENTERED,
                                  1024, 768,
                                  SDL_WINDOW_SHOWN
                                  );

    SDL_Renderer *renderer = SDL_CreateRenderer(MainWindow, -1, 0);

    SDL_SetRenderDrawColor(renderer, 255, 255, 255, 255);

    SDL_RenderClear(renderer);


    SDL_Texture *Tile = SDL_CreateTexture(renderer,SDL_PIXELFORMAT_RGBA8888,SDL_TEXTUREACCESS_TARGET,8,8);

    //I want my texture to be red
    SDL_SetTextureColorMod(Tile,255,0,0);

    //I just try this i dont know if I have to do that
    SDL_SetTextureAlphaMod(Tile,255);

    SDL_Rect destination = {320,240,8,8};
    SDL_RenderCopy(renderer,Tile,NULL,&destination);
    SDL_RenderPresent(renderer);
    SDL_Delay(3000);

    //Clean up
    SDL_DestroyTexture(Tile);
    SDL_DestroyWindow(MainWindow);
    SDL_Quit();

    return 0;
}

我也不知道我是否在 SDL_CreateTexture 中使用了正确的格式(SDL_PixelFormatEnum)值。他们有很多，我不明白他们的意思。 我可以使用哪一个来达到这个目的？

Answer 1

SDL_SetTextureColorMod将确保后续的渲染复制操作将考虑指定的乘数。它不会改变纹理纹素的颜色。

您应该加载位图或使用红色初始化纹理，如下例所示

int main(int argc, char* argv[]) {

    SDL_Init(SDL_INIT_EVERYTHING);

    SDL_Window *MainWindow = SDL_CreateWindow("My Game Window",
        SDL_WINDOWPOS_CENTERED,
        SDL_WINDOWPOS_CENTERED,
        1024, 768,
        SDL_WINDOW_SHOWN
        );

    SDL_Renderer *renderer = SDL_CreateRenderer(MainWindow, -1, 0);

    SDL_SetRenderDrawColor(renderer, 255, 255, 255, 255);

    SDL_RenderClear(renderer);

    SDL_Texture *Tile = SDL_CreateTexture(renderer, SDL_PIXELFORMAT_RGBA8888,
                        SDL_TEXTUREACCESS_STREAMING, 8, 8);

    // Initialize texture pixels to a red opaque RGBA value
    unsigned char* bytes = nullptr;
    int pitch = 0;
    SDL_LockTexture(Tile, nullptr, reinterpret_cast<void**>(&bytes), &pitch);
    unsigned char rgba[4] = { 255, 0, 0, 255 };
    for(int y = 0; y < 8; ++y) {
        for (int x = 0; x < 8; ++x) {
            memcpy(&bytes[(y * 8 + x)*sizeof(rgba)], rgba, sizeof(rgba));
        }
    }
    SDL_UnlockTexture(Tile);

    SDL_Rect destination = { 320, 240, 8, 8 };
    SDL_RenderCopy(renderer, Tile, NULL, &destination);
    SDL_RenderPresent(renderer);
    SDL_Delay(3000);

    //Clean up
    SDL_DestroyTexture(Tile);
    SDL_DestroyWindow(MainWindow);
    SDL_Quit();

    return 0;
}