draw bitmap using Opengl es in Android

Question

I have an android application that is drawing a 800*480 image on the screen. My phone is also 800*480 px. The phone is able to do the drawing in about 25 ms. Every few seconds i want to transition to another image which is also 800*480 by fading the alpha of the first image and increasing the alpha of the second image. While doing this the drawable.draw(canvas) call takes about 75 ms.

What can i do to reduce the drawing time during the transition phase? I have considered using OPENGL but i cannot figure it out.

Answer 1

Here is a simple example using OpenGL ES 1.0/1.1 and texture to draw bitmap to GLSurfaceView.

    private static class BitmapRenderer implements GLSurfaceView.Renderer {

    private int[] textures;

    private Resources resources;

    public BitmapRenderer(Resources resources) {
        this.resources = resources;
    }

    private static final float[] VERTEX_COORDINATES = new float[] {
            -1.0f, +1.0f, 0.0f,
            +1.0f, +1.0f, 0.0f,
            -1.0f, -1.0f, 0.0f,
            +1.0f, -1.0f, 0.0f
    };

    private static final float[] TEXTURE_COORDINATES = new float[] {
            0.0f, 0.0f,
            1.0f, 0.0f,
            0.0f, 1.0f,
            1.0f, 1.0f
    };

    private static final Buffer TEXCOORD_BUFFER = ByteBuffer.allocateDirect(TEXTURE_COORDINATES.length * 4)
            .order(ByteOrder.nativeOrder()).asFloatBuffer().put(TEXTURE_COORDINATES).rewind();
    private static final Buffer VERTEX_BUFFER = ByteBuffer.allocateDirect(VERTEX_COORDINATES.length * 4)
            .order(ByteOrder.nativeOrder()).asFloatBuffer().put(VERTEX_COORDINATES).rewind();

    @Override
    public void onSurfaceCreated(GL10 gl, EGLConfig config) {
        textures = new int[1];
        gl.glEnable(GL10.GL_TEXTURE_2D);
        gl.glEnableClientState(GL10.GL_VERTEX_ARRAY);
        gl.glEnableClientState(GL10.GL_TEXTURE_COORD_ARRAY);

        gl.glGenTextures(1, textures, 0);
        gl.glBindTexture(GL10.GL_TEXTURE_2D, textures[0]);

        gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_MAG_FILTER, GL10.GL_LINEAR);
        gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_MIN_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);

        GLUtils.texImage2D(GL10.GL_TEXTURE_2D, 0, BitmapFactory.decodeResource(resources, R.mipmap.ic_launcher), 0);
    }

    @Override
    public void onSurfaceChanged(GL10 gl, int width, int height) {
        gl.glViewport(0, 0, width, height);
    }

    @Override
    public void onDrawFrame(GL10 gl) {
        gl.glActiveTexture(GL10.GL_TEXTURE0);
        gl.glBindTexture(GL10.GL_TEXTURE_2D, textures[0]);

        gl.glVertexPointer(3, GL10.GL_FLOAT, 0, VERTEX_BUFFER);
        gl.glTexCoordPointer(2, GL10.GL_FLOAT, 0, TEXCOORD_BUFFER);
        gl.glDrawArrays(GL10.GL_TRIANGLE_STRIP, 0, 4);
    }
}

Then just use this Renderer in your GLSurfaceView

glSurfaceView.setEGLContextClientVersion(1);
glSurfaceView.setRenderer(new BitmapRenderer(getResources()));
glSurfaceView.setRenderMode(GLSurfaceView.RENDERMODE_WHEN_DIRTY);

Hope it would be helpful.

Answer 2

I had the same problem and found my performance in opengl. This tutorial got me started: http://obviam.net/index.php/texture-mapping-opengl-android-displaying-images-using-opengl-and-squares/