SDL_image png transparency

bgoska

Unregistered

Post: #1

Jan 11, 2005 — 09:44 AM

I've been trying to get transparency to work with SDL_image and pngs. I have a png image with the alpha channel, but when I display it nothing is affected.

Loading code

Code:

    //Init variables

    itsFileName = fileName;

    itsID = 0;

    itsStatus = false;

    SDL_Surface * TextureImage[1];

    int pixelFormat;

    if(fileName.substr(fileName.length() - 3) == "bmp") //if its a bmp

        {

            pixelFormat = GL_BGR_EXT;

        }

        else

        {

            pixelFormat = GL_RGBA;

        }

     //Try and load bitmap

         if ( ( TextureImage[0] = IMG_Load( fileName.c_str() ) ) )

         {

        itsStatus = true;

        //Generate texture

        glGenTextures( 1, &itsID );

        //Set our focus to new texture

        glBindTexture( GL_TEXTURE_2D, itsID );

        if(gluBuild2DMipmaps(GL_TEXTURE_2D, 3, TextureImage[0]->w, TextureImage[0]->h, pixelFormat, GL_UNSIGNED_BYTE, TextureImage[0]->pixels))

        {

                 itsStatus = false; //non-zero return = failure to load

            }

        //Set filtering for this texture to Linear, I don't know if this is needed - oh well works with it :)

        glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR );

        glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR );

            }

    if ( TextureImage[0] )

        SDL_FreeSurface( TextureImage[0] );

and the display code:

Code:

    glEnable(GL_BLEND);

    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

    glColor3f(1.0f,1.0f,1.0f);

    glBindTexture(GL_TEXTURE_2D, poly->getTextureID() );

    glBegin(GL_QUADS);

        glTexCoord2f( 0.0f, 1.0f ); glVertex2f(  0.0f,  poly->getYSize() );

        glTexCoord2f( 1.0f, 1.0f ); glVertex2f(  poly->getXSize(),  poly->getYSize() );

        glTexCoord2f( 1.0f, 0.0f ); glVertex2f(  poly->getXSize(),  0.0f );

        glTexCoord2f( 0.0f, 0.0f ); glVertex2f(  0.0f,  0.0f );        

    glEnd();

    glDisable(GL_BLEND);

I don't understand why it doesn't work, the image shows up but is not transparent at all. Thanks for the help!

ThemsAllTook

Moderator

Posts: 1,562
Joined: 2003.10

Post: #2

Jan 11, 2005 — 10:22 AM

I see a problem in your call to gluBuild2DMipmaps. The second parameter should be GL_RGBA. Passing 3 basically tells GL to discard any alpha channel you pass it in the texture image.

- Alex Diener

bgoska

Unregistered

Post: #3

Jan 11, 2005 — 12:59 PM

Oh, wow, I can't belive I over looked that. Thanks that fixed all my problems.

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