OpenGL textures loaded with SDL_Image display with no alpha

Started by ZachHinchy October 24, 2011 03:44 AM

0 comments, last by JTippetts 13 years, 1 month ago

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October 24, 2011 03:44 AM

I am making a game using OpenGL, with SDL_Image employed to load the textures. When drawn on screen, there's no alpha -- in an exact square around the opaque contents of the texture, black is drawn; outside that space, white is drawn. Here is my OpenGL init code...



    SDL_SetVideoMode(windowWidth, windowHeight, 16, SDL_HWSURFACE|SDL_GL_DOUBLEBUFFER|SDL_OPENGL);

    glClearColor(0, 0, 0, 0);

    glClearDepth(1.0f);

    glViewport(0, 0, windowWidth, windowHeight);

    glMatrixMode(GL_PROJECTION);

    glLoadIdentity();

    glOrtho(0, windowWidth, windowHeight, 0, 1, -1);

    glMatrixMode(GL_MODELVIEW);

    glEnable(GL_TEXTURE_2D);

    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

    glLoadIdentity();

...here is my image loading function...



    SDL_Surface *loadImage (const char *filename, bool alpha = true) {

        SDL_Surface* loadedImage = NULL;

        SDL_Surface* zoomedImage = NULL;

        SDL_Surface* optimizedImage = NULL;



        loadedImage = IMG_Load(filename);



        if (loadedImage != NULL) {

            zoomedImage = zoomSurface(loadedImage,windowScaleH/4,windowScaleH/4,SMOOTHING_ON);

            SDL_FreeSurface(loadedImage);



            if (alpha) optimizedImage = SDL_DisplayFormatAlpha(zoomedImage);

            else optimizedImage = SDL_DisplayFormat(zoomedImage);

            SDL_FreeSurface(zoomedImage);

        }



        return optimizedImage;

    }

...here is the code I actually use to create the GL texture...



    GLuint thisIsMyTexture;

    glGenTextures(1, &thisIsMyTexture);

    temporarySurface = loadImage("theimagetomytexture.png");

    glBindTexture(GL_TEXTURE_2D,thisIsMyTexture);

    glTexImage2D(GL_TEXTURE_2D, 0, 4, temporarySurface->w, temporarySurface->h, 0, GL_RGBA, GL_UNSIGNED_BYTE, temporarySurface->pixels);

    glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR );

    glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR );

...and the drawing code itself.



    glBindTexture(GL_TEXTURE_2D,thisIsMyTexture);

    glBegin( GL_QUADS );

        glTexCoord2f(0.0f, 0.0f); glVertex3f(0.0f, 0.0f, 1.0f);

        glTexCoord2f(1.0f, 0.0f); glVertex3f(32.0f, 0.0f, 1.0f);

        glTexCoord2f(1.0f, 1.0f); glVertex3f(32.0f, 32.0f, 1.0f);

        glTexCoord2f(0.0f, 1.0f); glVertex3f(0.0f, 32.0f, 1.0f);

    glEnd();

That's all the relevant information I can think of. Help would be appreciated!