如何从十六进制值的缓冲区渲染矩形SDL2纹理？

Question

I'm having some trouble understanding texture streaming and loading a 2D texture from an array of raw pixel data.

Here is my code:

#include <stdio.h>
#include <stdlib.h>

#include <SDL2/SDL.h>

#define WINDOW_W 640
#define WINDOW_H 320

int main(int argc, char *argv[])
{
    if (SDL_Init(SDL_INIT_EVERYTHING))
        exit(1);

    /* Set up main window. */
    SDL_Window *window = SDL_CreateWindow(
        "Texture Streaming",
        SDL_WINDOWPOS_CENTERED,
        SDL_WINDOWPOS_CENTERED,
        WINDOW_W,
        WINDOW_H,
        SDL_WINDOW_SHOWN
    );
    if (window == NULL)
        exit(2);

    /* Set up renderer. */
    SDL_Renderer *renderer = SDL_CreateRenderer(
        window,
        -1,
        SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC
    );
    if (renderer == NULL)
        exit(3);

    SDL_Event   ev;
    int         window_running = 1;

    SDL_Texture *texture = SDL_CreateTexture(renderer, SDL_PIXELFORMAT_RGBA32, SDL_TEXTUREACCESS_STATIC, 64, 32);
    Uint32 pixels[64 * 32];
    for (int i = 0; i < (64 * 32); i++)
        pixels[i] = 0xFF00FFFF;
    for (int i = 0; i < 64; i++)
        pixels[i] = 0xFF0000FF;
    SDL_UpdateTexture(texture, NULL, pixels, 4);

    while (window_running)
    {
        while (SDL_PollEvent(&ev) != 0)
        {
            if (ev.type == SDL_QUIT)
                window_running = 0;
        }
        SDL_SetRenderDrawColor(renderer, 0xFF, 0xFF, 0xFF, 0xFF);
        SDL_RenderClear(renderer);
        SDL_RenderCopy(renderer, texture, NULL, NULL);
        SDL_RenderPresent(renderer);
    }

    SDL_DestroyRenderer(renderer);
    SDL_DestroyWindow(window);
    SDL_Quit();

    return 0;
}

Instead of my program drawing the first 64 pixels red and the rest magenta, it just spits out a random chunk of red and yellow pixels.

I'm having trouble understanding SDL_CreateTexture and SDL_UpdateTexture.

Answer 1

Your pitch in UpdateTexture is wrong. Pitch is byte length of a row, not single pixel. In your case pitch is 64*4 .

Pixel format SDL_PIXELFORMAT_RGBA32 is alias to either SDL_PIXELFORMAT_RGBA8888 or SDL_PIXELFORMAT_ABGR8888 (latter in your case). Look at https://wiki.libsdl.org/SDL_PixelFormatEnum . So your 0xFF00FFFF is yellow (R=0xff, G=0xff, B=0, A=0xff).

Finally, if we're talking about texture streaming (ie updating every frame or otherwise very often), you should create streaming texture and use LockTexture/UnlockTexture. UpdateTexture is for static textures.