c++ - OpenGL + libpng : wrong colors on image

Question

自上周以来，我一直在尝试在屏幕上加载和显示 PNG。我使用库 libpng 将 png 复制到内存中，然后使用 glDrawPixels 在屏幕上显示它。结果如下:

原图:

“游戏”中的截图:

还有代码，我使用静态 Image::loadPNG 将 PNG 加载到 map 中，如下所示:

bool Image::loadPNG( std::string _image, FILE * file, unsigned char header[ 54 ] )
{
    fseek( file, 8, SEEK_SET );
    ImageData* imageData = new ImageData( );
    Image* image = new Image( );
    image->type = IMAGETYPE_PNG;
    imageData->image = image;
    png_structp png_ptr = png_create_read_struct( PNG_LIBPNG_VER_STRING, NULL, NULL, NULL );

    if( !png_ptr )
    {
        std::cout << "png_create_read_struct failed. " << std::endl;
        return false;
    }

    png_infop info_ptr = png_create_info_struct(png_ptr);

    if( !info_ptr )
    {
        std::cout << "png_create_info_struct failed. " << std::endl;
        return false;
    }

    if( setjmp( png_jmpbuf( png_ptr ) ) )
    {
        std::cout << "Error during init_io. " << std::endl;
        return false;
    }

    png_init_io( png_ptr, file );
    png_set_sig_bytes( png_ptr, 8 );
    png_read_info( png_ptr, info_ptr );
    png_set_strip_16( png_ptr );
    png_read_update_info(png_ptr, info_ptr);
    int bit_depth;
    int color;
    png_get_IHDR(png_ptr, info_ptr, &image->width, &image->height, &bit_depth, &color, NULL, NULL, NULL);
    png_read_update_info(png_ptr, info_ptr);
    int pitch = png_get_rowbytes(png_ptr, info_ptr);
    image->image = new unsigned char[pitch * image->height];
    png_bytep* row_pointers = new png_bytep[image->height];

    for (int y = 0; y < image->height; y++)
        row_pointers[image->height - 1 - y] = image->image + y * pitch;

    png_read_image(png_ptr, row_pointers);
    delete[] row_pointers;

    // tym na razie dupy sobie nie zawracam

    Image::images.insert( std::pair< std::string, ImageData* >( _image, imageData ) );
    glGenTextures(1, &imageData->texture);
    glBindTexture( GL_TEXTURE_2D, imageData->texture );
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, image->width, image->height, 0, GL_BGRA_EXT, GL_UNSIGNED_BYTE, image->image);
    gluBuild2DMipmaps( GL_TEXTURE_2D, 4, image->width, image->height, GL_RGBA, GL_UNSIGNED_BYTE, image->image );
    return true;
}

最后在 OpenGL 中显示它:

Image* image = Image::images["f.png"]->image;

if( image )
{
    glDisable(GL_DEPTH_TEST);
    glPushMatrix( );
    //glPixelStorei(GL_UNPACK_ALIGNMENT, 4);  

    float nx = 0.0f;
    float ny = 0.0f;

    glLoadIdentity( );
    glTranslatef( 0, 0, -1 );

    if( nx > 0 || ny > 0 )
        glRasterPos2f( nx, ny );

    else
    {
        glRasterPos2f( 0, 0 );
        glBitmap(0,0,0,0, nx, ny, NULL);
    }

    glDrawPixels( image->width, image->height, GL_RGBA, GL_UNSIGNED_BYTE, image->image);
    glPopMatrix( );
    glEnable(GL_DEPTH_TEST);
}

如您所见，颜色与应有的颜色不同。谁能帮我弄清楚如何解决我的问题？

Answer 1

看起来您可能交换了一些颜色 channel 。在对 glTexImage2D() 的调用中，尝试将 GL_BGRA_EXT 更改为 GL_RGBA，我想。或者，如果这不起作用，请将 GL_UNSIGNED_BYTE 更改为 GL_UNSIGNED_INT_8_8_8_8_REV。