TexturePNG.cc

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#include <esg/texture/TexturePNG.h>
#include <png.h>

using namespace esg;

#define PNG_BYTES_TO_CHECK 4
TexturePNG::TexturePNG(const char* path)
{
    /* Open the prospective PNG file. */
    FILE *fp = fopen(path, "rb");
    if (!fp) {
        fprintf(stderr,"TexturePNG::TexturePNG(): Unable to open file `%s'\n", path);
        return;
    }

    /* Read in some of the signature bytes */
    png_byte buf [PNG_BYTES_TO_CHECK];
    if (fread(buf, 1, PNG_BYTES_TO_CHECK, fp) != PNG_BYTES_TO_CHECK) {
        fprintf(stderr,"TexturePNG::TexturePNG(): Unable to read file `%s'\n", path);
        return;
    }

    /* Compare the first PNG_BYTES_TO_CHECK bytes of the signature.
       Proceed if they match */
    if (png_sig_cmp(buf, (png_size_t)0, PNG_BYTES_TO_CHECK)) {
        fprintf(stderr,"TexturePNG::TexturePNG(): File `%s' is not in PNG format\n", path);
        return;
    }

    /* Create and initialize the png_struct. REQUIRED */
    png_structp png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING,
                                                 NULL, NULL, NULL);
    if (!png_ptr) {
        fclose(fp);
        fprintf(stderr,"TexturePNG::TexturePNG(): Error in PNG structure initialization\n");
        return;
    }

    /* Allocate/initialize the memory for image information. REQUIRED. */
    png_infop info_ptr = png_create_info_struct(png_ptr);
    if (!info_ptr)
    {
        fclose(fp);
        png_destroy_read_struct(&png_ptr, png_infopp_NULL, png_infopp_NULL);
        fprintf(stderr,"TexturePNG::TexturePNG(): Error in PNG info initialization\n");
        return;
    }

    /* Set error handling if you are using the setjmp/longjmp method (this is
     * the normal method of doing things with libpng).  REQUIRED unless you
     * set up your own error handlers in the png_create_read_struct() earlier.
     */

    if (setjmp(png_jmpbuf(png_ptr))) {
        /* Free all of the memory associated with the png_ptr and info_ptr */
        png_destroy_read_struct(&png_ptr, &info_ptr, png_infopp_NULL);
        fclose(fp);
        /* If we get here, we had a problem reading the file */
        fprintf(stderr,"TexturePNG::TexturePNG(): Error in PNG error handling\n");
        return;
    }

    /* Set up the input control if you are using standard C streams. REQUIRED*/
    png_init_io(png_ptr, fp);

    /* We have already read some of the signature */
    png_set_sig_bytes(png_ptr, PNG_BYTES_TO_CHECK);

    /*
     * If you have enough memory to read in the entire image at once,
     * and you need to specify only transforms that can be controlled
     * with one of the PNG_TRANSFORM_* bits (this presently excludes
     * dithering, filling, setting background, and doing gamma
     * adjustment), then you can read the entire image (including
     * pixels) into the info structure with this call:
     */
    png_read_png(png_ptr, info_ptr,
                 PNG_TRANSFORM_STRIP_16|PNG_TRANSFORM_PACKING|PNG_TRANSFORM_EXPAND,
                 NULL);


    
    /*
     * At this point you have read the entire image
     */
    
    
    png_bytepp row_pointers = png_get_rows(png_ptr, info_ptr);

    _allocate_texture(png_get_image_width(png_ptr, info_ptr),
                      png_get_image_height(png_ptr, info_ptr));

    for (register unsigned i = 0; i < _height; i++) 
        for (register unsigned j = 0; j < _width; j++) 
            _texture[i][j].set((float)row_pointers[i][3*j+0]/(float)0xFF,
                               (float)row_pointers[i][3*j+1]/(float)0xFF,
                               (float)row_pointers[i][3*j+2]/(float)0xFF);

    /* clean up after the read, and free any memory allocated - REQUIRED */
    png_destroy_read_struct(&png_ptr, &info_ptr, png_infopp_NULL);

    /* close the file */
    fclose(fp);
}
#undef PNG_BYTES_TO_CHECK

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