把png图片资源转换为framebuffer可显示数据

    我们都知道，我们是通过framebuffer来显示图片的，但是我们有不能直接把png图片显示到framebuffer，因为framebuffer是不能直接识别png图片的。

    我们如何把一个1.png图片转换为framebuffer需要的格式呢？

1. 了解framebuffer的大小

# cat /sys/class/graphics/fb0/window_axis                                      
0 0 1919 1079

我们查看fb0是1920*1080的大小

2. 查看需要显示的图片的大小及位数

32 bit的 500 x 333 的图片

3. 把图片转换为framebuffer的格式

#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include "png.h"


static int open_png(const char* name, 
                                    png_structp* png_ptr, 
                                    png_infop* info_ptr,
                                    png_uint_32* width, 
                                    png_uint_32* height, 
                                    png_byte* channels){  
    unsigned char header[8];  
    size_t bytesRead;  
    int result = 0;  
    FILE* fp = NULL;  
    //png_structp png_ptr = NULL;  
    //png_infop info_ptr = NULL;  
    int color_type, bit_depth;  
    //png_uint_32 width;  
    //png_uint_32 height;  
    //png_byte channels;  
  
    fp = fopen(name, "rb");  
    if (fp == NULL) {  
        result = -1;  
        goto exit;  
    }  
  
    bytesRead = fread(header, 1, sizeof(header), fp);  
    if (bytesRead != sizeof(header)) {  
        result = -2;  
        goto exit;  
    }  
  
    if (png_sig_cmp(header, 0, sizeof(header))) {  
        result = -3;  
        goto exit;  
    }  
  
    *png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);  
    if (!*png_ptr) {  
        result = -4;  
        goto exit;  
    }  
  
    *info_ptr = png_create_info_struct(*png_ptr);  
    if (!*info_ptr) {  
        result = -5;  
        goto exit;  
    }  
  
    if (setjmp(png_jmpbuf(*png_ptr))) {  
        result = -6;  
        goto exit;  
    }  
  
    png_init_io(*png_ptr, fp);  
    png_set_sig_bytes(*png_ptr, sizeof(header));  
    png_read_info(*png_ptr, *info_ptr);  
  
    png_get_IHDR(*png_ptr, *info_ptr, width, height, &bit_depth,  
            &color_type, NULL, NULL, NULL);  
  
    *channels = png_get_channels(*png_ptr, *info_ptr);  
  
    printf("pnginfo bit_depth:%d, channels:%d, color_type:%d\n", bit_depth, *channels, color_type);

    return result;
  
exit:  
    if (fp != NULL) {  
        fclose(fp);  
        fp = NULL;  
    }  
  
    return result;  
      
}


// Copy 'input_row' to 'output_row', transforming it to the
// framebuffer pixel format.  The input format depends on the value of
// 'channels':
//
//   1 - input is 8-bit grayscale
//   3 - input is 24-bit RGB
//   4 - input is 32-bit RGBA/RGBX
//
// 'width' is the number of pixels in the row.
static void transform_rgb_to_draw(unsigned char* input_row,
                                  unsigned char* output_row,
                                  int channels, int width) {
    int x;
    unsigned char* ip = input_row;
    unsigned char* op = output_row;

    switch (channels) {
        case 1:
            // expand gray level to RGBX
            for (x = 0; x < width; ++x) {
                *op++ = *ip;
                *op++ = *ip;
                *op++ = *ip;
                *op++ = 0xff;
                ip++;
            }
            break;

        case 3:
            // expand RGBA to RGBX
            for (x = 0; x < width; ++x) {
                *op++ = *ip++;
                *op++ = *ip++;
                *op++ = *ip++;
                *op++ = 0xff;
            }
            break;

        case 4:
            // copy RGBA to RGBX
            memcpy(output_row, input_row, width*4);
            break;
    }
}

  
int main(int argc ,char **argv) {
    int result = 0;
    png_structp png_ptr = NULL;
    png_infop info_ptr = NULL;
    png_uint_32 width, height;
    png_byte channels;

    // 获取png图片的宽 高等属性
    result = open_png("./1.png", &png_ptr, &info_ptr, &width, &height, &channels);
    if (result < 0) return result;

    printf("width:%d   height:%d\n", width, height);

    //申请存放图片的内存大小
    unsigned char *data = (unsigned char *)malloc(width*height*4);
    if (data == NULL) return -1;

    png_set_bgr(png_ptr);
    int y = 0;
    unsigned char *p_row = (unsigned char*)(malloc(width * 4));
    //把每一行数据读取出来，并转换为rgb值
    for (y = 0; y < height; ++y) {
        png_read_row(png_ptr, p_row, NULL);
        transform_rgb_to_draw(p_row, data + y * (width * 4), channels, width);
    }
    free(p_row);
    //free(data);

    //申请framebuffer大小的内存
    unsigned char *data_out = (unsigned char *)malloc(1920*1080*4);
    if (data_out == NULL) return -1;

    memset(data_out, 0, 1920*1080*4);
    unsigned char* src_p = data;
    // 显示到坐标（300，400）的地址处
    unsigned char* dst_p = data_out + 300*(1920*4) + 400*(4);
    int i;
    int j;
    int h;
    int w;
    h = height;
    w = width;
    //透明度处理
    for (i = 0; i < h; ++i) {
        if (4 == 4) {
            unsigned char *p0 = src_p;
            unsigned char *p1 = dst_p;
            unsigned char alpha = 255;
            for (j = 0; j < w; j++) {
                alpha = *(p0+3);
                *p1 = (*p1 * (255-alpha) + *p0++ * alpha) / 255;
                ++p1;
                *p1 = (*p1 * (255-alpha) + *p0++ * alpha) / 255;
                ++p1;
                *p1 = (*p1 * (255-alpha) + *p0++ * alpha) / 255;
                ++p1;
                *p1++ = 255;
                ++p0;
            }
        } else {
            //memcpy(dst_p, src_p, w * source->pixel_bytes);
        }
        src_p += width*4;
        dst_p += 1920*4;
    }
    free(data);

    //存储为本地文件
    FILE *p_o = fopen("./fb0.img", "wb+");
    if (p_o == NULL) {
        printf("open out file failed!\n");
        return -1;
    }
    int len = fwrite(data_out, 1, 1920*1080*4, p_o);
    fclose(p_o);

    free(data_out);
    return 0;
}  

我们把转换后的数据存储为本地文件fb0.img

4. 我们在界面显示1.png

直接在串口下：busybox dd if=/udisk/fb0.img  of=/dev/graphics/fb0,  即可在界面显示1.png图片了