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677

answers:

3

Hi guys,

Well, here's my request. I don't know OpenGL already, and I'm not willing to learn it, I want to learn OpenGL ES directly since I'm targeting my development to android, however. I want to learn openGL ES in order to develop my 2D games, I choosed that for performances purpose (since basic SurfaceView drawing isn't that efficient when it comes to RT games). My question is: Where to start ? I've spent over a month browsing google and reading/trying some tutorials/examples I've found anywhere but to be honnest, it didn't help much and this is for two reasons: 1- Almost all the articles/tutorials I've came across are 3D related (I only want to learn how to do my 2D Sprites drawing) 2- There's no base to start from since all the articles targets a specific things like: "How to draw a triangle (with vertices)", "How to create a Mesh"... etc

I've tried to read some source code too (ex.: replica island) but the codes are too complicated and contains a lot of things that aren't necessary; result: I get lost among 100 .java files with weird class names and stuff (:P)

I guess there's no course like the one I'm looking for, but i'll be very glad if somebody could give me some guidelines and some links maybe to learn what I'm up to (Only OpenGL ES 2D Sprites rendering ! Nothing 3D)

Thank you very much for reading my posting, and I'm looking forward to hearing from you

Best regards

+3  A: 

2D programming is just 3D programming that's constrained to a plane. You'll have no choice but to learn 3D, but when you're using it just set z = 0.

There is an offical book on OpenGL ES. That might give you the intro that you're after: http://www.amazon.com/OpenGL-ES-2-0-Programming-Guide/dp/0321502795/

No one in particular
To be pedantic, you still use Z so that you can let the hardware do sorting for you. The big change is that (likely) the 2D application will use an orthographic view instead of a perspective one.
dash-tom-bang
Thank you very much for your answer, your statement shows me that I was wrong about the Opengl and Opengl ES definition.
Miloud B.
+1  A: 

I would definately checkout Android - Chris Pruett Google IO lecture Writing real-time games for Android redux

grab the PDF also

it's really helpful on many levels, Chris has really great experience with creating games for mobile devices

but if you are really focused on 2D then start with Canvas http://developer.android.com/guide/topics/graphics/index.html#drawing-with-canvas

Another option depends on skill level is Flash+AdobeAIR to Android, I myself like and luv programming level and as you further start developing you will find out why.

OpenGL : Check for - Nehe Productions

a couple of apps you may want to put on your phone that is worth it and they are free is: OpenGL Demo, min3d Framework, RedBook Sample

Atom Arcade
+2  A: 

I was in a similar situation.
The way I started with openGL with start by looking at the very basic GLSurfaceView samples/demos.

Start, by setting up your app activity, and set up the basic canvas.

Take a loot at the replica island source code file: GameRenderer.java for how to setup your canvas with the proper GL flags for 2D (sprite) rendering. You should really take a look at SpriteMethodTest by the same author of replica island: http://code.google.com/p/apps-for-android/source/browse/trunk/SpriteMethodTest

See this question where I posted my own code: http://stackoverflow.com/questions/3597323/using-opengl-to-replace-canvas-android/3607943#3607943

After you have your canvas set up, you start by calling something like: gl.glClear(GL10.GL_COLOR_BUFFER_BIT);

After that you're ready to render a sprite. First, you'll need to load the sprite into a texture: http://qdevarena.blogspot.com/2009/02/how-to-load-texture-in-android-opengl.html

However, this is the tutorial that really helped me out with loading sprites: http://tkcodesharing.blogspot.com/2008/05/working-with-textures-in-androids.html

This is how I do it, I have a class named Texture.java:

public class Texture
{
    /*Begin public declarations*/
    public float x = 0;
    public float y = 0;
    public float z = 0;
    public float width = 0;
    public float height = 0;
    /*Begin Private Declarations*/
    private GL10 gl;
    public int[] texture;    //holds the texture in integer form
    private int texture_name;
    private int[] mCropWorkspace;
    private final BitmapFactory.Options sBitmapOptions;


/*Begin Methods*/
public Texture( GL10 gl_obj )
{
    gl = gl_obj;
    texture = new int[1];
    mCropWorkspace = new int[4];
    sBitmapOptions = new BitmapFactory.Options();
    sBitmapOptions.inPreferredConfig = Bitmap.Config.RGB_565;
    //Log.d(TAG, "Initializing Texture Object");
}    
public int get_texture_name( )
{
    return texture_name;
}

/*Loads the resource to memory*/
public boolean Load( Bitmap bitmap ) //rename this to glLoad and don't have it as an initializer parameter
{
    /*many thanks to sprite method test if this works*/
    if ( gl == null )
    {
        Log.e(TAG, "Failed to load resource.  Context/GL is NULL");
        return false;
    }
    int error;

    int textureName = -1;
    gl.glGenTextures(1, texture, 0);
    textureName = texture[0];

    //Log.d(TAG, "Generated texture: " + textureName);
    gl.glBindTexture(GL10.GL_TEXTURE_2D, textureName);
    gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_MIN_FILTER, GL10.GL_NEAREST);
    gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_MAG_FILTER, GL10.GL_LINEAR);
    gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_WRAP_S, GL10.GL_CLAMP_TO_EDGE);
    gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_WRAP_T, GL10.GL_CLAMP_TO_EDGE);
    gl.glTexEnvf(GL10.GL_TEXTURE_ENV, GL10.GL_TEXTURE_ENV_MODE, GL10.GL_REPLACE);

    GLUtils.texImage2D(GL10.GL_TEXTURE_2D, 0, bitmap, 0);

    mCropWorkspace[0] = 0;
    mCropWorkspace[1] = bitmap.getHeight();
    mCropWorkspace[2] = bitmap.getWidth();
    mCropWorkspace[3] = -bitmap.getHeight();

    ((GL11) gl).glTexParameteriv(GL10.GL_TEXTURE_2D, 
            GL11Ext.GL_TEXTURE_CROP_RECT_OES, mCropWorkspace, 0);

    error = gl.glGetError();
    if (error != GL10.GL_NO_ERROR)
    { 
        Log.e(TAG, "GL Texture Load Error: " + error);

    }
    //Log.d(TAG, "Loaded texture: " + textureName);
    return true;
}

}

Then in my onDrawFrame() method I simply do:

Texture texture = ...
gl.glBindTexture(GL10.GL_TEXTURE_2D, texture.texture[0]);
((GL11Ext) gl).glDrawTexfOES((float)(draw_x + 0.5), (float)(draw_y + 0.5), 0, tile_width, tile_height);

That should get you going with drawing 2D sprites on an openGL canvas. I've noticed that there is really no straightforward tutorial on this. Hopefully in the future I will post one in my dev blog: http://developingthedream.blogspot.com/

Good luck.

Miguel Morales
Dude thank you very much ! I've never gotten directions like these, that's exactly what I was looking for ! And I'll keep an eye on your blog, hopefully you'll provide us with a great tutorials in the future :), Again thank you very much
Miloud B.