SDL Surface Pixel Format Conversion - c++

Question

I want to convert an SDL_Surface, which was loaded by IMG_Load() to an other pixel format (rgba8) for an OpenGL Texture. How can I do that?
I've read about SDL_ConvertSurface() in the documentation, but I can't figure out, how to put it together.

Answer 1

Give "How To Load an OpenGL Texture from an SDL_Surface" a shot:
GLuint texture; // This is a handle to our texture object
SDL_Surface *surface; // This surface will tell us the details of the image
GLenum texture_format;
GLint nOfColors;
if( (surface = SDL_LoadBMP("image.bmp")) )
{
// Check that the image's width is a power of 2
if( (surface->w & (surface->w - 1)) != 0 )
{
printf("warning: image.bmp's width is not a power of 2\n");
}
// Also check if the height is a power of 2
if( (surface->h & (surface->h - 1)) != 0 )
{
printf("warning: image.bmp's height is not a power of 2\n");
}
// get the number of channels in the SDL surface
nOfColors = surface->format->BytesPerPixel;
if( nOfColors == 4 ) // contains an alpha channel
{
if(surface->format->Rmask == 0x000000ff)
texture_format = GL_RGBA;
else
texture_format = GL_BGRA;
}
else if( nOfColors == 3 ) // no alpha channel
{
if(surface->format->Rmask == 0x000000ff)
texture_format = GL_RGB;
else
texture_format = GL_BGR;
}
else
{
printf("warning: the image is not truecolor.. this will probably break\n");
// this error should not go unhandled
}
// Have OpenGL generate a texture object handle for us
glGenTextures( 1, &texture );
// Bind the texture object
glBindTexture( GL_TEXTURE_2D, texture );
// Set the texture's stretching properties
glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR );
glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR );
// Edit the texture object's image data using the information SDL_Surface gives us
glTexImage2D
(
GL_TEXTURE_2D,
0,
nOfColors,
surface->w,
surface->h,
0,
texture_format,
GL_UNSIGNED_BYTE,
surface->pixels
);
}
else
{
printf("SDL could not load image.bmp: %s\n", SDL_GetError());
SDL_Quit();
return 1;
}
// Free the SDL_Surface only if it was successfully created
if( surface )
{
SDL_FreeSurface( surface );
}