OpenGL Xcode加入libpng库-2

1.在控制台安装MacPorts软件安装工具

2.使用MacPorts安装libpng

命令为：sudo port install libpng

3.在xcode的工程设置中的 Header Search Paths添加/opt/local/include/

4.在xcode的工程设置中的Library Search Paths添加/opt/local/lib/

通过上面四步后理论上可以使用png库了,在代码中#include <png.h>即可

但是在链接时会报错：

解决方法:

1.于是我将/opt/local/lib/里的libpng16.a文件拷到了工程文件夹中

2.右键点击项目，选择右键菜单的"Add files to xxx...."

3.选择要使用的静态库libpng16.a

4.添加静态库文件之后，在项目导航中和“Linked Frameworks and Libraries" 中可以看到刚刚加入的静态库

之后编译链接成功

PS:libpng库另一种安装方法

1.直接从官网上下载libpng库的zip包

2.然后在控制台执行下列指令

cp ./scripts/makefile.darwin makefile

make

sudo make install

make clean

之后包的头文件和库文件就会安装到/opt/local/include/和/opt/local/lib/中

使用libpng库读取png文件

在其他OpenGL程序中调用ReadPNGFromFile 这个函数即可

struct gl_texture_t
{
    GLsizei width;
    GLsizei height;
    GLenum format;
    GLint internalFormat;
    GLuint id;
    GLubyte *texels;
};

void GetPNGtextureInfo(int color_type,  gl_texture_t *texinfo)
{
    switch (color_type)
    {
        case PNG_COLOR_TYPE_GRAY:
            texinfo->format = GL_LUMINANCE;
            texinfo->internalFormat = 1;
            break;
            
        case PNG_COLOR_TYPE_GRAY_ALPHA:
            texinfo->format = GL_LUMINANCE_ALPHA;
            texinfo->internalFormat = 2;
            break;
            
        case PNG_COLOR_TYPE_RGB:
            texinfo->format = GL_RGB;
            texinfo->internalFormat = 3;
            break;
            
        case PNG_COLOR_TYPE_RGB_ALPHA:
            texinfo->format = GL_RGBA;
            texinfo->internalFormat = 4;
            break;
            
        default:
            /* Badness */
            break;
    }
}

gl_texture_t *ReadPNGFromFile(const char *filename)
{
    gl_texture_t *texinfo;
    png_byte magic[8];
    png_structp png_ptr;
    png_infop info_ptr;
    int bit_depth, color_type;
    FILE *fp = NULL;
    png_bytep *row_pointers = NULL;
    png_uint_32 w, h;
    int i;
    /* Open image file */
    fp = fopen(filename, "rb");
    if (!fp)
    {
        fprintf(stderr, "error: couldn't open \"%s\"!\n", filename);
        return NULL;
    }
    /* Read magic number */
    fread(magic, 1, sizeof(magic), fp);
    /* Check for valid magic number */
    if (!png_check_sig(magic, sizeof(magic)))
    {
        fprintf(stderr, "error: \"%s\" is not a valid PNG image!\n", filename);
        fclose(fp);
        return NULL;
    }
    /* Create a png read struct */
    png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
    if (!png_ptr)
    {
        fclose(fp);
        return NULL;
    }
    /* Create a png info struct */
    info_ptr = png_create_info_struct(png_ptr);
    if (!info_ptr)
    {
        fclose(fp);
        png_destroy_read_struct(&png_ptr, NULL, NULL);
        return NULL;
    }
    /* Create our OpenGL texture object */
    texinfo = (gl_texture_t *)malloc(sizeof(gl_texture_t));
    /* Initialize the setjmp for returning properly after a libpng error occured */
    if (setjmp(png_jmpbuf(png_ptr)))
    {
        fclose(fp);
        png_destroy_read_struct(&png_ptr, &info_ptr, NULL);
        if (row_pointers) free(row_pointers);
        if (texinfo) {
            if (texinfo->texels)
                free(texinfo->texels);
            free(texinfo);
        }
        return NULL;
    }
    /* Setup libpng for using standard C fread() function with our FILE pointer */
    png_init_io(png_ptr, fp);
    /* Tell libpng that we have already read the magic number */
    png_set_sig_bytes(png_ptr, sizeof(magic));
    /* Read png info */
    png_read_info(png_ptr, info_ptr);
    /* Get some usefull information from header */
    bit_depth = png_get_bit_depth(png_ptr, info_ptr);
    color_type = png_get_color_type(png_ptr, info_ptr);
    /* Convert index color images to RGB images */
    if (color_type == PNG_COLOR_TYPE_PALETTE)
        png_set_palette_to_rgb(png_ptr);
    /* Convert 1-2-4 bits grayscale images to 8 bits grayscale. */
    if (color_type == PNG_COLOR_TYPE_GRAY && bit_depth < 8)
        png_set_expand_gray_1_2_4_to_8(png_ptr);
    
    if (png_get_valid(png_ptr, info_ptr, PNG_INFO_tRNS))
        png_set_tRNS_to_alpha(png_ptr);
    if (bit_depth == 16) png_set_strip_16(png_ptr);
    else if (bit_depth < 8) png_set_packing(png_ptr);
    /* Update info structure to apply transformations */
    png_read_update_info(png_ptr, info_ptr);
    /* Retrieve updated information */
    png_get_IHDR(png_ptr, info_ptr, &w, &h, &bit_depth, &color_type, NULL, NULL, NULL);
    texinfo->width = w;
    texinfo->height = h;
    /* Get image format and components per pixel */
    GetPNGtextureInfo(color_type, texinfo);
    /* We can now allocate memory for storing pixel data */
    texinfo->texels = (GLubyte *)malloc(sizeof(GLubyte) * texinfo->width * texinfo->height * texinfo->internalFormat);
    /* Setup a pointer array. Each one points at the begening of a row. */
    row_pointers = (png_bytep *)malloc(sizeof(png_bytep) * texinfo->height);
    for (i = 0; i < texinfo->height; ++i)
    {
        row_pointers[i] = (png_bytep)(texinfo->texels + ((texinfo->height - (i + 1)) * texinfo->width * texinfo->internalFormat));
    }
    /* Read pixel data using row pointers */
    png_read_image(png_ptr, row_pointers);
    /* Finish decompression and release memory */
    png_read_end(png_ptr, NULL);
    png_destroy_read_struct(&png_ptr, &info_ptr, NULL);
    /* We don't need row pointers anymore */
    free(row_pointers);
    fclose(fp);
    return texinfo;
}