stb

读写使用一个头文件，可以不使用libpng，libjpeg等等库，好处是更为简单，使用opengl时极其简单。
定义STB_IMAGE_IMPLEMENTATION，预处理器会修改头文件，让其只包含相关的函数定义源码，将这个头文件包含源代码

#include 
#define STB_IMAGE_IMPLEMENTATION
#include "stb_image.h"

int main(int argc, const char * argv[]) {
    int width, height, nrChannels;
    unsigned char *data = stbi_load("test.jpg", &width, &height, &nrChannels, 0);
    printf("w %d, h %d, c %dn", width, height, nrChannels);
    
    return 0;
}

注意时rgba的写入，四字节

#include 
#define STB_IMAGE_WRITE_IMPLEMENTATION
#include "stb_image_write.h"

#define STB_IMAGE_IMPLEMENTATION
#include "stb_image.h"
int main(int argc, char** argv)
{
    int w, h, n;
    //rgba
    unsigned char *data = stbi_load("test.png", &w, &h, &n, 0);
    printf("%d, %d, %dn", w, h, n);
    //rgba
    for (int dx = 0; dx < 10; ++dx)
    {
        data[n * w * 10 + dx * n + 0] = 255;
        data[n * w * 10 + dx * n + 1] = 255;
        data[n * w * 10 + dx * n + 2] = 128;
        data[n * w * 10 + dx * n + 3] = 100;
     }
    //write image
    stbi_write_png("write.png", w, h, n, data, w * n);
    stbi_image_free(data);
    return 0;
}