C++ 如何解析 ppm 文件？

Question

I'm trying to parse a ppm file.

The spec is this: http://netpbm.sourceforge.net/doc/ppm.html

Example:

P3
# feep.ppm
4 4
15
 0  0  0    0  0  0    0  0  0   15  0 15
 0  0  0    0 15  7    0  0  0    0  0  0
 0  0  0    0  0  0    0 15  7    0  0  0
15  0 15    0  0  0    0  0  0    0  0  0

The stuff after the "15" are the rgb values of all pixels in the give image.

I have tried this so far:

void read_and_draw_ppm_file() {
    ifstream infile;
    infile.open(TEXTURE_FILE.c_str());
    string line;
    int count = 0;
    while (getline(infile, line) && count < 4) {
        count++;
    }


    char c;

    int red = -1, green = -1, blue = -1;
    int rgb_count = 0;
    for (int i = 0; i < TEXTURE_WIDTH; i++) {
        for (int j = 0; j < TEXTURE_HEIGHT; j++) {


              infile >> c;


            if (rgb_count == 0) {
                if (red != -1 && blue != -1 && green != -1) {
                    cout << red<<endl;
                    cout << green<<endl;
                    cout << blue<<endl;


                    uint32_t colour = (255 << 24) + (int(red) << 16) + (int(green) << 8) + int(blue);
                    window.setPixelColour(i, j, colour);

                     red = -1;
                    blue = -1;
                    green = -1;
                }
                red = (int) (unsigned char) c;
                rgb_count++;

            } else if (rgb_count == 1) {
                green = (int) (unsigned char) c;
                rgb_count++;
            } else if (rgb_count == 2) {
                blue = (int) (unsigned char) c;
                rgb_count = 0;
            }
        }

    }
    infile.close();
}

The idea is to basically extract triplets of 3 bytes, then convert each to rgb respectively.

Problem is, when I display the image into the screen, the image isn't quite the same as it's supposed to be.

Where am I going wrong?

The original image:

Rendered Image image:

Answer 1

You read in a value for red , then increment j . Then you read in green , and increment j . Next you read blue , store the pixel value, and increment j .

So you're writing out your values spaced out every 3 rows.