Question

I’m putting together a simple test made up of two tutorials available online for OpenGL ES on Android. This is really just so that I can learn about the basics of OpenGL ES to better understand how I have to design my program.

Right now, when it tries to render, the mouse movement effect works, but I get no square drawn on the screen.

Here are the two source files I’m dealing with:

import javax.microedition.khronos.egl.EGLConfig;
import javax.microedition.khronos.opengles.GL10;
import android.opengl.GLSurfaceView;
import android.opengl.GLU;

//Simple clear-screen renderer.
class ClearRenderer implements GLSurfaceView.Renderer {

    private float mRed;
    private float mGreen;
    private float mBlue;

    private TileUI testTile;

    public ClearRenderer() {

        this.testTile = new TileUI();

    }

    public void onSurfaceCreated(GL10 gl, EGLConfig config) {

        gl.glShadeModel(GL10.GL_SMOOTH);
        gl.glClearColor(0.0f, 0.0f, 0.0f, 0.5f);
        gl.glClearDepthf(1.0f);
        gl.glEnable(GL10.GL_DEPTH_TEST);
        gl.glDepthFunc(GL10.GL_LEQUAL);
        gl.glHint(GL10.GL_PERSPECTIVE_CORRECTION_HINT, GL10.GL_NICEST); 

    }

    public void onSurfaceChanged(GL10 gl, int w, int h) {

        gl.glViewport(0, 0, w, h);
        gl.glMatrixMode(GL10.GL_PROJECTION);
        gl.glLoadIdentity();

        // Calculate The Aspect Ratio Of The Window
        GLU.gluPerspective(gl, 45.0f, (float)w / (float)h, 0.1f, 100.0f);

        gl.glMatrixMode(GL10.GL_MODELVIEW);
        gl.glLoadIdentity();

    }

    public void onDrawFrame(GL10 gl) {

        gl.glClearColor(mRed, mGreen, mBlue, 1.0f);
        gl.glClear(GL10.GL_COLOR_BUFFER_BIT | GL10.GL_DEPTH_BUFFER_BIT);
        gl.glLoadIdentity();
        gl.glTranslatef(0.0f, 0.0f, 0.0f);
        testTile.draw(gl);

    }

    public void setColor(float r, float g, float b) {
        mRed = r;
        mGreen = g;
        mBlue = b;
    }

}

The second one is the tile object itself:

import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.FloatBuffer;

import javax.microedition.khronos.opengles.GL10;

public class TileUI {

    private float[] vertices = {
        -1.0f, -1.0f,  0.0f,        // Bottom left
         1.0f, -1.0f,  0.0f,        // Bottom right
        -1.0f,  1.0f,  0.0f,        // Top left
         1.0f,  1.0f,  0.0f         // Top right
    };

    private FloatBuffer vertexBuffer;

    public TileUI() {

        ByteBuffer byteBuf = ByteBuffer.allocateDirect(vertices.length * 4);
        byteBuf.order(ByteOrder.nativeOrder());
        vertexBuffer = byteBuf.asFloatBuffer();
        vertexBuffer.put(vertices);
        vertexBuffer.position(0);

    }

    // Performs the actual drawing of a Tile.
    public void draw(GL10 gl) {

        // Set the face rotation.
        gl.glFrontFace(GL10.GL_CW);
        // Point to our vertex buffer.
        gl.glVertexPointer(3, GL10.GL_FLOAT, 0, vertexBuffer);

        // Enable vertex buffer.
        gl.glEnableClientState(GL10.GL_VERTEX_ARRAY);
        // Draw the vertices as a triangle strip.
        gl.glDrawArrays(GL10.GL_TRIANGLE_STRIP, 0, vertices.length / 3);
        // Disable the client state before leaving.
        gl.glDisableClientState(GL10.GL_VERTEX_ARRAY);      

    }

}

I will definitely apologize in advance, this is a bit of a Frankenstein, any help and explanation about what’s going on here would be greatly appreciated.

Answer 1

I think that the line that’s causing you problems is gl.glTranslatef(0.0f, 0.0f, 0.0f);. That means that you are drawing your quad at the origin and that’s also where the camera is so you don’t see it. Try something like gl.glTranslatef(0.0f, 0.0f, -10.0f);. That should move the quad into the screen and put it in front of your camera. Alternatively, if you’re doing 2D drawing you could use glOrtho() instead of gluPerspective() and that will give you an orthographic, or flat, projection.