GLdc/samples/loadbmp.c

// quick and dirty bitmap loader...for 24 bit bitmaps with 1 plane only.
// See http://www.dcs.ed.ac.uk/~mxr/gfx/2d/BMP.txt for more info.

#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>

#include "loadbmp.h"

int ImageLoad(char *filename, Image *image) {
    FILE *file;
    size_t size;                        // size of the image in bytes.
    size_t i;                           // standard counter.
    int32_t sizeX, sizeY;               // width/height of the image - must be 4 bytes to match the file format
    int16_t planes;                     // number of planes in image (must be 1)
    int16_t bpp;                        // number of bits per pixel (must be 24)
    char temp;                          // temporary color storage for bgr-rgb conversion.

    // make sure the file is there.
    if ((file = fopen(filename, "rb"))==NULL) {
        printf("File Not Found : %s\n",filename);
        return 0;
    }

    // seek through the bmp header, up to the width/height:
    fseek(file, 10, SEEK_CUR);

    uint32_t offset;
    fread(&offset, 4, 1, file);
    fseek(file, 4, SEEK_CUR);

    // read the width
    if ((i = fread(&sizeX, 4, 1, file)) != 1) {
        printf("Error reading width from %s.\n", filename);
        return 0;
    }
    image->sizeX = sizeX;
    printf("Width of %s: %d\n", filename, sizeX);

    // read the height
    if ((i = fread(&sizeY, 4, 1, file)) != 1) {
        printf("Error reading height from %s.\n", filename);
        return 0;
    }
    image->sizeY = sizeY;
    printf("Height of %s: %d\n", filename, sizeY);

    // calculate the size (assuming 24 bits or 3 bytes per pixel).
    size = image->sizeX * image->sizeY * 3;

    // read the planes
    if ((fread(&planes, 2, 1, file)) != 1) {
        printf("Error reading planes from %s.\n", filename);
        return 0;
    }
    if (planes != 1) {
        printf("Planes from %s is not 1: %u\n", filename, planes);
        return 0;
    }

    // read the bpp
    if ((i = fread(&bpp, 2, 1, file)) != 1) {
        printf("Error reading bpp from %s.\n", filename);
        return 0;
    }
    if (bpp != 24) {
        printf("Bpp from %s is not 24: %u\n", filename, bpp);
        return 0;
    }

    // seek past the rest of the bitmap header.
    fseek(file, offset, SEEK_SET);

    // read the data.
    image->data = (char *) malloc(size);
    if (image->data == NULL) {
        printf("Error allocating memory for color-corrected image data");
        return 0;
    }

    if ((i = fread(image->data, size, 1, file)) != 1) {
        printf("Error reading image data from %s.\n", filename);
        return 0;
    }

    for (i=0;i<size;i+=3) { // reverse all of the colors. (bgr -> rgb)
        temp = image->data[i];
        image->data[i] = image->data[i+2];
        image->data[i+2] = temp;
    }

    // we're done.
    return 1;
}