libpng库的安装与使用（交叉编译）

进入http://sourceforge.net/projects/libpng/files/下载一个libpng稳定版本源码包

libpng-1.2.56.tar.gz 下载地址点击这里！

tar -xzvf libpng-1.2.56.tar.gz 

d libpng-1.2.56                         /* 可以使用.configure --help来查看帮助信息 */

./configure --prefix=$PWD/tmp --host=arm-linux

make && make install

如果提示错误那么就需要安装zlib库文件，以前安装过现在就不安装了。

这是tmp目录下就生成bin  include  lib  share四个目录，这里我们只用到库文件和头文件，把库文件拷贝到开发板根文件系统，把库和头文件拷贝到交叉编译环境路径下。

我交叉编译环境如下：

/usr/local/arm/4.3.2/arm-none-linux-gnueabi/libc/usr/include     /* 头文件路径 */

/usr/local/arm/4.3.2/arm-none-linux-gnueabi/libc/armv4t/lib     /* 库文件路径 */

到现在我们就安装好了Libpng库文件，接下来我们用一个示例文件来演示。

mypng.c文件如下：

#include<stdio.h>#include<libpng12/png.h>#include <sys/types.h>#include <sys/stat.h>#include <fcntl.h>#include <sys/ioctl.h>#include <sys/mman.h>#include <linux/fb.h>#include <string.h>#include <stdlib.h>#define ERROR -1#define PNG_BYTES_TO_CHECK 4#define FB_DEVICE_NAME "/dev/fb0"//#define DBG_PRINTF printf#define DBG_PRINTF(...)#define HAVE_ALPHA 1#define NO_ALPHA 0static int g_lcd_fd;FILE   *g_png_fd;static struct fb_var_screeninfo g_tFBVar;static struct fb_fix_screeninfo g_tFBFix;static unsigned char *g_pucFBMem;static unsigned int g_dwScreenSize;static unsigned int g_dwLineWidth;static unsigned int g_dwPixelWidth;static int FBDeviceInit(void){int ret;g_lcd_fd = open(FB_DEVICE_NAME, O_RDWR);if (0 > g_lcd_fd){DBG_PRINTF("can't open %s\n", FB_DEVICE_NAME);}ret = ioctl(g_lcd_fd, FBIOGET_VSCREENINFO, &g_tFBVar);if (ret < 0){DBG_PRINTF("can't get fb's var\n");return -1;}ret = ioctl(g_lcd_fd, FBIOGET_FSCREENINFO, &g_tFBFix);if (ret < 0){DBG_PRINTF("can't get fb's fix\n");return -1;}g_dwScreenSize = g_tFBVar.xres * g_tFBVar.yres * g_tFBVar.bits_per_pixel / 8;g_pucFBMem = (unsigned char *)mmap(NULL , g_dwScreenSize, PROT_READ | PROT_WRITE, MAP_SHARED, g_lcd_fd, 0);if (0 > g_pucFBMem){DBG_PRINTF("can't mmap\n");return -1;}g_dwLineWidth  = g_tFBVar.xres * g_tFBVar.bits_per_pixel / 8;g_dwPixelWidth = g_tFBVar.bits_per_pixel / 8;return 0;}static int FBShowPixel(int iX, int iY, unsigned int dwColor){unsigned char *pucFB;unsigned short *pwFB16bpp;unsigned int *pdwFB32bpp;unsigned short wColor16bpp; /* 565 */int iRed;int iGreen;int iBlue;if ((iX >= g_tFBVar.xres) || (iY >= g_tFBVar.yres)){DBG_PRINTF("out of region\n");return -1;}pucFB      = g_pucFBMem + g_dwLineWidth * iY + g_dwPixelWidth * iX;pwFB16bpp  = (unsigned short *)pucFB;pdwFB32bpp = (unsigned int *)pucFB;switch (g_tFBVar.bits_per_pixel){case 8:{*pucFB = (unsigned char)dwColor;break;}case 16:{iRed   = (dwColor >> (16+3)) & 0x1f;iGreen = (dwColor >> (8+2)) & 0x3f;iBlue  = (dwColor >> 3) & 0x1f;wColor16bpp = (iRed << 11) | (iGreen << 5) | iBlue;*pwFB16bpp= wColor16bpp;break;}case 32:{*pdwFB32bpp = dwColor;break;}default :{DBG_PRINTF("can't support %d bpp\n", g_tFBVar.bits_per_pixel);return -1;}}return 0;}static int FBCleanScreen(unsigned int dwBackColor){unsigned char *pucFB;unsigned short *pwFB16bpp;unsigned int *pdwFB32bpp;unsigned short wColor16bpp; /* 565 */int iRed;int iGreen;int iBlue;int i = 0;pucFB      = g_pucFBMem;pwFB16bpp  = (unsigned short *)pucFB;pdwFB32bpp = (unsigned int *)pucFB;switch (g_tFBVar.bits_per_pixel){case 8:{memset(g_pucFBMem, dwBackColor, g_dwScreenSize);break;}case 16:{iRed   = (dwBackColor >> (16+3)) & 0x1f;iGreen = (dwBackColor >> (8+2)) & 0x3f;iBlue  = (dwBackColor >> 3) & 0x1f;wColor16bpp = (iRed << 11) | (iGreen << 5) | iBlue;while (i < g_dwScreenSize){*pwFB16bpp= wColor16bpp;pwFB16bpp++;i += 2;}break;}case 32:{while (i < g_dwScreenSize){*pdwFB32bpp= dwBackColor;pdwFB32bpp++;i += 4;}break;}default :{DBG_PRINTF("can't support %d bpp\n", g_tFBVar.bits_per_pixel);return -1;}}return 0;}int FBShowLine(int iXStart, int iXEnd, int iY, unsigned char *pucRGBArray){int i = iXStart * 3;int iX;unsigned int dwColor;if (iY >= g_tFBVar.yres)return -1;if (iXStart >= g_tFBVar.xres)return -1;if (iXEnd >= g_tFBVar.xres){iXEnd = g_tFBVar.xres;}for (iX = iXStart; iX < iXEnd; iX++){/* 0xRRGGBB */dwColor = (pucRGBArray[i]<<16) + (pucRGBArray[i+1]<<8) + (pucRGBArray[i+2]<<0);i += 3;FBShowPixel(iX, iY, dwColor);}return 0;}int check_if_png(char *file_name){   char buf[PNG_BYTES_TO_CHECK];   /* Open the prospective PNG file. */   if ((g_png_fd = fopen(file_name, "rb")) == NULL)   {      printf("open %s  is fail\n",file_name);return 0;   }   /* Read in some of the signature bytes */   if (fread(buf, 1, PNG_BYTES_TO_CHECK, g_png_fd) != PNG_BYTES_TO_CHECK)      return 0;   /* Compare the first PNG_BYTES_TO_CHECK bytes of the signature.      Return nonzero (true) if they match */   /* Close the file */   fclose(g_png_fd);    return(!png_sig_cmp(buf, (png_size_t)0, PNG_BYTES_TO_CHECK));}int read_png_data(char *filepath)/* 用于解码png图片 */{ png_bytep *row_pointers; png_structp png_ptr; png_infop  info_ptr; int        temp; int color_type,channels,i; int width,height,bit_depth,flag;  g_png_fd = fopen(filepath, "rb"); if(g_png_fd == NULL) /* 文件打开失败 */ {return -1;  } /* 初始化各种结构 */ 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 rewind(g_png_fd); /*开始读文件*/ png_init_io(png_ptr, g_png_fd); // 读文件了 png_read_png(png_ptr, info_ptr, PNG_TRANSFORM_EXPAND, 0); /*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*/ width = png_get_image_width(png_ptr, info_ptr); height = png_get_image_height(png_ptr, info_ptr); 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*/  /* row_pointers里边就是rgba数据 */ row_pointers = png_get_rows(png_ptr, info_ptr);  if(channels == 4 || color_type == PNG_COLOR_TYPE_RGB_ALPHA) {/*如果是RGB+alpha通道，或者RGB+其它字节*/   flag = HAVE_ALPHA;    /* 标记 */   temp = (4 * width);/* 每行有4 * out->width个字节 */    for(i = 0; i < height; i++){FBShowLine(0, temp, height, &row_pointers[i]);} } else if(channels == 3 || color_type == PNG_COLOR_TYPE_RGB) {/* 如果是RGB通道 */flag = NO_ALPHA;    /* 标记 */ printf("width=%d\n",width);printf("height=%d\n",height);printf("bit_depth=%d\n",bit_depth);  temp = (3 * width);/* 每行有3 * out->width个字节 */  printf("row_pointers=%d\n",sizeof(row_pointers));  int j;  for(i = 0; i <height; i++)  {FBShowLine(0, temp, i, &row_pointers[i]);for(j=0;j<temp;j+=3){DBG_PRINTF("row_pointers[%d][%d]=0x%x\n",i,j,row_pointers[i][j]);DBG_PRINTF("row_pointers[%d][%d]=0x%x\n",i,j+1,row_pointers[i][j+1]);DBG_PRINTF("row_pointers[%d][%d]=0x%x\n",i,j+2,row_pointers[i][j+2]);}  } } else  return -1;  /* 撤销数据占用的内存 */ png_destroy_read_struct(&png_ptr, &info_ptr, 0);  return 0;}int main(int argc,char **argv){int i;if(argc!=2){DBG_PRINTF("Usage: \n");DBG_PRINTF("%s <png_file>\n", argv[0]);return -1;}if (FBDeviceInit()){return -1;}FBCleanScreen(0);i=check_if_png(argv[1]);if(i==0){DBG_PRINTF("this is not png image file\n");}read_png_data(argv[1]);return 0;}

这样就可以在LCD上显示png图片了。