libpng样例

读取png文件：

#include <stdio.h>#include <png.h> #include <stdlib.h>/******************************图片数据*********************************/typedef struct _pic_data pic_data;struct _pic_data{intwidth, height;/* 尺寸 */intbit_depth;/* 位深 */intflag;/* 一个标志，表示是否有alpha通道 */unsigned char**rgba;/* 图片数组 */};/**********************************************************************/#define PNG_BYTES_TO_CHECK 4#define HAVE_ALPHA1#define NO_ALPHA0int detect_png(char *filepath, pic_data *out)/* 用于解码png图片 */{FILE *pic_fp;pic_fp = fopen(filepath, "rb");if(pic_fp == NULL) /* 文件打开失败 */return -1;/* 初始化各种结构 */png_structp png_ptr;png_infop   info_ptr;char        buf[PNG_BYTES_TO_CHECK];int         temp;png_ptr  = png_create_read_struct(PNG_LIBPNG_VER_STRING, 0, 0, 0);info_ptr = png_create_info_struct(png_ptr);setjmp(png_jmpbuf(png_ptr)); // 这句很重要temp = fread(buf,1,PNG_BYTES_TO_CHECK,pic_fp);temp = png_sig_cmp((void*)buf, (png_size_t)0, PNG_BYTES_TO_CHECK);/*检测是否为png文件*/if (temp!=0) return 1;rewind(pic_fp);/*开始读文件*/png_init_io(png_ptr, pic_fp);// 读文件了png_read_png(png_ptr, info_ptr, PNG_TRANSFORM_EXPAND, 0);int color_type,channels;/*获取宽度，高度，位深，颜色类型*/channels       = png_get_channels(png_ptr, info_ptr);/*获取通道数*/out->bit_depth = png_get_bit_depth(png_ptr, info_ptr);/* 获取位深 */color_type     = png_get_color_type(png_ptr, info_ptr);/*颜色类型*/int i,j;int size, pos = 0;/* row_pointers里边就是rgba数据 */png_bytep* row_pointers;row_pointers = png_get_rows(png_ptr, info_ptr);out->width = png_get_image_width(png_ptr, info_ptr);out->height = png_get_image_height(png_ptr, info_ptr);size = out->width * out->height; /* 计算图片的总像素点数量 */ if(channels == 4 || color_type == PNG_COLOR_TYPE_RGB_ALPHA){/*如果是RGB+alpha通道，或者RGB+其它字节*/ size *= (4*sizeof(unsigned char));/* 每个像素点占4个字节内存 */out->flag = HAVE_ALPHA;/* 标记 */out->rgba = (unsigned char**) malloc(size);if(out->rgba == NULL){/* 如果分配内存失败 */fclose(pic_fp);puts("错误(png):无法分配足够的内存供存储数据!");return 1;}temp = (4 * out->width);/* 每行有4 * out->width个字节 */for(i = 0; i < out->height; i++){for(j = 0; j < temp; j += 4){/* 一个字节一个字节的赋值 */out->rgba[0][pos] = row_pointers[i][j]; // redout->rgba[1][pos] = row_pointers[i][j+1]; // greenout->rgba[2][pos] = row_pointers[i][j+2];   // blueout->rgba[3][pos] = row_pointers[i][j+3]; // alpha++pos;}}}else if(channels == 3 || color_type == PNG_COLOR_TYPE_RGB){/* 如果是RGB通道 */size *= (3*sizeof(unsigned char));/* 每个像素点占3个字节内存 */out->flag = NO_ALPHA;/* 标记 */out->rgba = (unsigned char**) malloc(size);if(out->rgba == NULL){/* 如果分配内存失败 */fclose(pic_fp);puts("错误(png):无法分配足够的内存供存储数据!");return 1;}temp = (3 * out->width);/* 每行有3 * out->width个字节 */for(i = 0; i < out->height; i++){for(j = 0; j < temp; j += 3){/* 一个字节一个字节的赋值 */out->rgba[0][pos] = row_pointers[i][j]; // redout->rgba[1][pos] = row_pointers[i][j+1]; // greenout->rgba[2][pos] = row_pointers[i][j+2];   // blue++pos;}}}else return 1;/* 撤销数据占用的内存 */png_destroy_read_struct(&png_ptr, &info_ptr, 0); return 0;}

 生成png文件：

int write_png_file(char *file_name , pic_data *graph)/* 功能：将LCUI_Graph结构中的数据写入至png文件 */{int j, i, temp, pos;png_byte color_type; png_structp png_ptr;png_infop info_ptr; png_bytep * row_pointers;/* create file */FILE *fp = fopen(file_name, "wb");if (!fp){printf("[write_png_file] File %s could not be opened for writing", file_name);return -1;}/* initialize stuff */png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);if (!png_ptr){printf("[write_png_file] png_create_write_struct failed");return -1;}info_ptr = png_create_info_struct(png_ptr);if (!info_ptr){printf("[write_png_file] png_create_info_struct failed");return -1;}if (setjmp(png_jmpbuf(png_ptr))){printf("[write_png_file] Error during init_io");return -1;}png_init_io(png_ptr, fp);/* write header */if (setjmp(png_jmpbuf(png_ptr))){printf("[write_png_file] Error during writing header");return -1;}/* 判断要写入至文件的图片数据是否有透明度，来选择色彩类型 */if(graph->flag == HAVE_ALPHA) color_type = PNG_COLOR_TYPE_RGB_ALPHA;else color_type = PNG_COLOR_TYPE_RGB;png_set_IHDR(png_ptr, info_ptr, graph->width, graph->height,graph->bit_depth, color_type, PNG_INTERLACE_NONE,PNG_COMPRESSION_TYPE_BASE, PNG_FILTER_TYPE_BASE);png_write_info(png_ptr, info_ptr);/* write bytes */if (setjmp(png_jmpbuf(png_ptr))){printf("[write_png_file] Error during writing bytes");return -1;}if(graph->flag == HAVE_ALPHA) temp = (4 * graph->width);else temp = (3 * graph->width);pos = 0;row_pointers = (png_bytep*)malloc(graph->height*sizeof(png_bytep));for(i = 0; i < graph->height; i++){row_pointers[i] = (png_bytep)malloc(sizeof(unsigned char)*temp);for(j = 0; j < temp; j += 4){row_pointers[i][j]   = graph->rgba[0][pos]; // redrow_pointers[i][j+1] = graph->rgba[1][pos]; // greenrow_pointers[i][j+2] = graph->rgba[2][pos];   // blueif(graph->flag == HAVE_ALPHA) row_pointers[i][j+3] = graph->rgba[3][pos]; // alpha++pos;}}png_write_image(png_ptr, row_pointers);/* end write */if (setjmp(png_jmpbuf(png_ptr))){printf("[write_png_file] Error during end of write");return -1;}png_write_end(png_ptr, NULL);    /* cleanup heap allocation */for (j=0; j<graph->height; j++)free(row_pointers[j]);free(row_pointers);    fclose(fp);    return 0;}