CODEWITHSUNDEEP
androidopengl-es-2.0
kishidp
kishidp

Reputation: 1948

loading a drawable resource into a texture and rendering it

I'm trying to understand OpenGL ES 2.0 in android. I got a code from a tutorial, but I do not understand how the texture works. I can't even understand where the rendering took place. Here is the code I got.

@Override
public void surfaceCreated(GL10 gl) {
    // set up the surface
    gl.glDisable(GL10.GL_DITHER);
    gl.glHint(
        GL10.GL_PERSPECTIVE_CORRECTION_HINT,
        GL10.GL_FASTEST);
    gl.glClearColor(0.4f, 0.2f, 0.2f, 0.5f);
    gl.glShadeModel(GL10.GL_SMOOTH);
    gl.glEnable(GL10.GL_DEPTH_TEST);
    // fetch the checker-board
    initImage(gl);
}
@Override
public void drawFrame(GL10 gl) {
    gl.glClear(GL10.GL_COLOR_BUFFER_BIT | GL10.GL_DEPTH_BUFFER_BIT);
    gl.glMatrixMode(GL10.GL_MODELVIEW);
    gl.glLoadIdentity();
    GLU.gluLookAt(gl, 0, 0, -5, 0f, 0f, 0f, 0f, 1.0f, 0.0f);
    gl.glEnableClientState(GL10.GL_VERTEX_ARRAY);
    gl.glEnableClientState(GL10.GL_TEXTURE_COORD_ARRAY);
    // apply the checker-board to the shape
    gl.glActiveTexture(GL10.GL_TEXTURE0);
    gl.glTexEnvx(
        GL10.GL_TEXTURE_ENV,
        GL10.GL_TEXTURE_ENV_MODE,
        GL10.GL_MODULATE);
    gl.glTexParameterx(
        GL10.GL_TEXTURE_2D,
        GL10.GL_TEXTURE_WRAP_S,
        GL10.GL_REPEAT);
    gl.glTexParameterx(
        GL10.GL_TEXTURE_2D,
        GL10.GL_TEXTURE_WRAP_T,
        GL10.GL_REPEAT);
    // animation
    int t = (int) (SystemClock.uptimeMillis() % (10 * 1000L));
    gl.glTranslatef(6.0f - (0.0013f * t), 0, 0);
    // draw
    gl.glFrontFace(GL10.GL_CCW);
    gl.glVertexPointer(3, GL10.GL_FLOAT, 0, vertexBuf);
    gl.glEnable(GL10.GL_TEXTURE_2D);
    gl.glTexCoordPointer(2, GL10.GL_FLOAT, 0, textureBuf);
    gl.glDrawElements(
        GL10.GL_TRIANGLE_STRIP,
        5,
        GL10.GL_UNSIGNED_SHORT, indexBuf);
}

private void initImage(GL10 gl) {
    int[] textures = new int[1];
    gl.glGenTextures(1, textures, 0);
    gl.glBindTexture(GL10.GL_TEXTURE_2D, textures[0]);
    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);
    InputStream in = context.getResources().openRawResource(R.drawable.cb);
    Bitmap image;
    try { image = BitmapFactory.decodeStream(in); }
    finally {
        try { in.close(); } catch(IOException e) { }
    }
    GLUtils.texImage2D(GL10.GL_TEXTURE_2D, 0, image, 0);
    image.recycle();
}

Can anyone explain to me where the image is loaded from a drawable file, where the conversion to texture, and where the rendering took place? I just can't seem to understand this. I'm familiar with how to do it in OpenGL but it seems OpenGL ES 2.0 uses a different technique?

Upvotes: 2

Views: 3128

Answers (1)

Tim
Tim

Reputation: 35933

GLUtils.texImage2D(GL10.GL_TEXTURE_2D, 0, image, 0); is a utility function which converts an android Bitmap into an OpenGL texture.

When this is called, it stores the bitmap in image into the currently bound texture, which in your case is textures[0].

glDrawElements is the command that actually fires off the rendering call. If you want to know what any of the other functions do, I suggest taking a look at their online help pages.

Upvotes: 4

Related Questions