Android OpenGL ES and 2D

问题:

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 chose it 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 honest, 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.

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).

回答1:

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: Using OpenGL to replace Canvas - Android

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/

回答2:

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/

回答3:

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

回答4:

You can see the project： https://github.com/ChillingVan/android-openGL-canvas/blob/master/README-en.md This implements canvas with OpenGL. It is pure Java. It implements parts of what normal canvas can do.

回答5:

I see a lot of good info has already been provided. I wanted to share a site that helped get up to speed on OpenGLE quick! It only took a few months and had a custom coordinate system based on the Cartesian coordinate system. I was able to render 3D object no camera using Augmented Reality techniques.

I started with only programming experience, with no OpenGL experience. I used Ray Wenderlich's tutorials site. The information provided there is top notch and easy to comprehend. He cuts through most of the superfluous information and provides what you need to know to be productive quickly. I highly recommend this tutorial as the starting point: http://www.raywenderlich.com/5223/beginning-opengl-es-2-0-with-glkit-part-1

The other resource I'd recommend is a book by Erik M Buck, titled Learning OpenGL ES for iOS.

Some criticized it saying it was too simplistic. But that's exactly what I was looking for. It helped me understand all of the basics and gave me an idea on where i should go next to learn more advanced stuff. But not surprisingly, I was able to build my augmented reality app using the simple techniques i'd learned from Ray's site and Erik's book. Thanks to them both for sharing!!!

回答6:

There are a lot of online tutorials that you can follow, but for a beginner nothing can replace this one: A real Open GL ES 2.0 2D tutorial