LWJGL/OpenGL - Alpha not working using GL_QUAD_STRIP or GL_LINE_STRIP

Question

I want to use Alpha/Blend mode for future stuff (transactions mainly and possible image blending) .

Well, I can't get it to work using LWJGL (GL1.1), I already tried other blend modes but didn't worked, nor changing the background or anything like that...

Screenshots:

1. http://i.imgur.com/cHU4YGS.png - GL_BLEND always enabled, everything is transparent
2. http://i.imgur.com/sPmPqne.png - GL_BLEND enabled on QUAD and text, I can see the line that is on disabled GL_BLEND
3. i imgur com/nkda41v png - GL_BLEND disabled on everything but the text -> I need some reputation to post more than 2 links, sorry about that but I belive this image is important so i'll post it anyway. Just fill with dots

The results are the same with or without alpha argument on all these tests

Code:

`    private void init() {
        try {
            Display.setDisplayMode(new DisplayMode(DEFAULT_WIDTH, DEFAULT_HEIGHT));
            Display.setResizable(true);
            Display.setVSyncEnabled(true);
            Display.setTitle(DEFAULT_TITLE + " v" + VERSION);
            Display.create();
            updateMatrix();
        } catch(LWJGLException e) {
            e.printStackTrace();
        }
        Keyboard.enableRepeatEvents(true);
        glEnable(GL_BLEND);
        glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);


    Font consolas = new Font("consolas", Font.PLAIN, 13);
    font = new TrueTypeFont(consolas, antiAliasedFont);
}

private void updateMatrix() {
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glOrtho(0, DEFAULT_WIDTH, DEFAULT_HEIGHT, 0, 1, -1);
    //glScaled((double) DEFAULT_WIDTH / (double) Display.getWidth(), (double) DEFAULT_HEIGHT / (double) Display.getHeight(), 0);
    glViewport(0, 0, Display.getWidth(), Display.getHeight());
    glMatrixMode(GL_MODELVIEW);
}

@Override
public void run() {
    init();
    Main main = Main.getMain();

    while(!Display.isCloseRequested()) {
        currentGraphicsTick++;
        {
            glClear(GL_COLOR_BUFFER_BIT);
            glClearColor(0f, 0f, 0f, 1f);

            if(Display.wasResized()) updateMatrix();
            if(vsyncMode == 1) Display.setVSyncEnabled(true);
            else if(vsyncMode == 2) Display.setVSyncEnabled(false);

            if(Display.isActive()) {
                glPushMatrix();
                try { // Draw
                    float alpha = (float) Math.cos(Math.toRadians(currentGraphicsTick % 90));
                    System.out.println("Alpha: " + alpha);

                    glBegin(GL_LINE_STRIP);
                    {
                        float sin = (float) Math.abs(Math.sin(Math.toRadians(currentGraphicsTick % 360)));
                        new Color(0.7f, 0.7f, 0.7f, alpha).bind();
                        glVertex2f(DEFAULT_WIDTH * 0.03f, DEFAULT_HEIGHT * 0.05f);
                        glVertex2f(DEFAULT_WIDTH * 0.93f * sin, DEFAULT_HEIGHT * 0.95f * sin);
                    }
                    glEnd();

                    glBegin(GL_QUAD_STRIP);
                    {
                        new Color(0.5f, 0.5f, 0.5f, alpha).bind();
                        glVertex2i(0, 0);
                        glVertex2i(0, DEFAULT_HEIGHT);
                        glVertex2i(DEFAULT_WIDTH, 0);
                        glVertex2i(DEFAULT_WIDTH, DEFAULT_HEIGHT);
                    }
                    glEnd();

                    String[] split = main.getGameLoopThread().getDebugString().split("\n");
                    for(int i = 0; i < split.length; i++) {
                        font.drawString(1, 1 + (i * font.getLineHeight()), split[i], Color.white);
                    }
                } catch(Throwable throwable) {
                    throwable.printStackTrace();
                }
                glPopMatrix();
            }

            Display.update();
            Display.sync(TARGET_FPS);
        }
    }
    Display.destroy();
    closeRequested = true;
}

I already tried:

1. Removing the 'alpha' argument from the Slick's Color constructor
2. Using OpenGL's glColor with and without alpha argument
3. Disabling/Enabling GL_BLEND in part of the code (I know some things wouldn't work, but you never know, right?)
4. Used constants to the alpha variable (such as 0.3f, 0.5f, 0.7f, 1f) instead of making it variable through Math.sin / cos using the tick as the degree
5. Using glRect(...)
6. Changing the background
7. Removing the glClearColor
8. Removing glClear (nice effect, never did this lol)

What I expect to see was a fading moving LINE_STRIP:

• On one side it moves from the (0, 0) to (width - 7%, height - 5%)

• On the other it stand still on (width + 3%, height + 5%)

• the rectangle would make it fade (the original idea would use the same color as the background, but it didn't on my tests because I want to see the rectangle)

Answer 1

I've had a similar(in terms of what I had to tackle) when doing a 2D game using my own engine. LWJGL's blend functions always have a few issues and there aren't really that many concrete answers for them as it really boils down to your code and how you placed things.

I presume you're using SlickUtil, and to that I would say write your own (or of course search around) your own methods for this. Util's methods were always somewhat wonky with blending.

1. Removing alpha shouldn't have changed much in terms of getting what you want
2. The only time I explicitly enable GL_BLEND is when rendering lights(always presuming you're doing 3D) and when I would render textures
3. I suggest not removing glClearColor, that doesn't directly affect your situation as long as you put it in the correct place

---

Like I said this bug/problem could be due to quite a few things that I can't quite pin-point from what you've posted.

My suggestions are:

1. Organise the whole project well to be able to point bugs out quickly
2. Make alot of stuff generic ASAP(Doesn't matter if you just want to quickly write something)
3. Avoid SlickUtil, it's great and I LOVE it but it does get it's issues

---

Sorry I can't help too much but tracking down your issue from the jumbled up code you posted is a bit difficult. I'll keep my eye on this question in case I may be of help in the future.

Answer 2

Besides the tips from @Juxhin, what fixed my problem with alpha blend was TextureImpl.bindNone(); from SlickUtils (check openGL's similar below)

This method is similar to glDisable(GL_TEXTURE_2D) before rendering the thing that needs to be blent (I know that searching and checking Slick's source)