Question

I am currently trying to make a game in Android.
I have this piece of code and I’m trying to display the square at one corner of the screen.
I’ve tried to use GLU.gluOrtho2D but every time I use it I get a blank screen.
Can someone tell me how to move the square from the center of the screen to one of the corners?

This is my code:

public class OpenGLRenderer implements Renderer {

private TexturedSquare element;
private float angle; 

public OpenGLRenderer(Context context) {
    // Initialize things
    int[] bilder = {R.drawable.first};
    element = new TexturedSquare(context, 1f, 1, bilder);
    angle = 0.5f;
}

public void onSurfaceCreated(GL10 gl, EGLConfig config) {

    // Set the background color to black ( rgba )
    gl.glClearColor(1f, 1f, 1f, 1f);
    // Enable Smooth Shading, default not really needed
    gl.glShadeModel(GL10.GL_SMOOTH);// OpenGL docs
    // Depth buffer setup.
    gl.glClearDepthf(1.0f);
    // Enables depth testing.
    gl.glEnable(GL10.GL_DEPTH_TEST);
    // The type of depth testing to do.
    gl.glDepthFunc(GL10.GL_LEQUAL);
    // Really nice perspective calculations.
    gl.glHint(GL10.GL_PERSPECTIVE_CORRECTION_HINT,
                      GL10.GL_NICEST);
    // NEW
    element.loadTexture(gl);             // Load images into textures (NEW)
    gl.glEnable(GL10.GL_TEXTURE_2D);
}


public void onDrawFrame(GL10 gl) {

    // Clears the screen and depth buffer.
    gl.glClear(GL10.GL_COLOR_BUFFER_BIT | GL10.GL_DEPTH_BUFFER_BIT);
    // Replace the current matrix with the identity matrix
    gl.glLoadIdentity();
    // Translates 4 units into the screen.
    gl.glTranslatef(0f, 0f, -4f);
    // What is to be drawn on the screen
    //gl.glRotatef(-angle*20f, 0f, 0f, 1f); // Rotate the element around 3 axes
    //gl.glRotatef(angle, 0f, 1f, 0f);
    //gl.glRotatef(angle, 0f, 0f, 1f);
    element.draw(gl);
    angle++;
}


public void onSurfaceChanged(GL10 gl, int width, int height) {

    // Sets the current view port to the new size.
    gl.glViewport(0, 0, width, height);
    // Select the projection matrix
    gl.glMatrixMode(GL10.GL_PROJECTION);
    // Reset the projection matrix
    gl.glLoadIdentity();// OpenGL docs.
    // Calculate the aspect ratio of the window
    GLU.gluPerspective(gl, 45.0f,
                               (float) width / (float) height,
                               0.1f, 100.0f);
    // Select the modelview matrix
    gl.glMatrixMode(GL10.GL_MODELVIEW);
    // Reset the modelview matrix
    gl.glLoadIdentity();
}
}

This is the draw method the square class uses:

public void draw(GL10 gl) {
  gl.glFrontFace(GL10.GL_CCW);

  gl.glFrontFace(GL10.GL_CCW); // OpenGL docs
    // Enable face culling.
  gl.glEnable(GL10.GL_CULL_FACE); // OpenGL docs
    // What faces to remove with the face culling.
  gl.glCullFace(GL10.GL_BACK); // OpenGL docs

  gl.glEnableClientState(GL10.GL_VERTEX_ARRAY);
  gl.glEnableClientState(GL10.GL_TEXTURE_COORD_ARRAY);
  gl.glVertexPointer(3, GL10.GL_FLOAT, 0, vertexBuffer);
  gl.glTexCoordPointer(2, GL10.GL_FLOAT, 0, texBuffer);

  gl.glPushMatrix();
  gl.glTranslatef(0f, 0f, cubeHalfSize);
  gl.glBindTexture(GL10.GL_TEXTURE_2D, textureIDs[0]);
  gl.glDrawArrays(GL10.GL_TRIANGLE_STRIP, 0, 4);
  gl.glPopMatrix();

  gl.glDisableClientState(GL10.GL_VERTEX_ARRAY);
  gl.glDisableClientState(GL10.GL_TEXTURE_COORD_ARRAY);
}

Any help?

Answer 1

Look at gl.glTranslatef(0f, 0f, cubeHalfSize);

if cubeHalfSize a positive value the cube won’t display.

You already have a “glTranslatef” in your OpenGLRenderer class so try commenting out “glTranslatef” in your square class:

  gl.glPushMatrix();
  gl.glTranslatef(0f, 0f, cubeHalfSize);
  gl.glBindTexture(GL10.GL_TEXTURE_2D, textureIDs[0]);
 // gl.glDrawArrays(GL10.GL_TRIANGLE_STRIP, 0, 4);
  gl.glPopMatrix();