Question

Previously I did a Tutorial on OpenGL-ES 1.0. For reference, this can be found here:
SpaceInvaders (it’s in german though)

My goal now is to port the game to OpenGL-ES 2.0. So far, I am able to load meshes and textures and render them.

Now I would like to have a simple rectangle as my background with a texture on it. This should be rendered in Ortho-Perspective. I then change to Projection-Perspective and draw a simple box. When I now call setLookAtM(…), I get a blank sceen. Here is the code:

public void onDrawFrame(GL10 gl) {
   long currentFrameStart = System.nanoTime();
   deltaTime = (currentFrameStart - lastFrameStart) / 1000000000.0f;
   lastFrameStart = currentFrameStart;

   GLES20.glClear(GLES20.GL_COLOR_BUFFER_BIT | GLES20.GL_DEPTH_BUFFER_BIT);
   GLES20.glUseProgram(programHandle);
   checkGlError("glUseProgram");

   mMVPMatrixHandle = GLES20.glGetUniformLocation(programHandle, "uMVPMatrix");
   mMVMatrixHandle = GLES20.glGetUniformLocation(programHandle, "uMVMatrix");
   mLightPosHandle = GLES20.glGetUniformLocation(programHandle, "uLightPos");
   mTextureUniformHandle = GLES20.glGetUniformLocation(programHandle, "uTexture");

   mPositionHandle = GLES20.glGetAttribLocation(programHandle, "aPosition");
   mColorHandle = GLES20.glGetAttribLocation(programHandle, "aColor");
   mNormalHandle = GLES20.glGetAttribLocation(programHandle, "aNormal");
   mTextureCoordinateHandle = GLES20.glGetAttribLocation
      (programHandle,"aTexCoordinate");

   Matrix.setIdentityM(mLightModelMatrix, 0);
   Matrix.multiplyMV(mLightPosInWorldSpace, 0, mLightModelMatrix, 0,    
      mLightPosInModelSpace, 0);
   Matrix.multiplyMV(mLightPosInEyeSpace, 0, mViewMatrix, 0, mLightPosInWorldSpace, 0);

   Matrix.orthoM(mProjectionMatrix, 0, -width / 2, width / 2, -height / 2, height / 2, 
      0, 100);
   drawBackground();

   GLES20.glEnable(GLES20.GL_CULL_FACE);

   Matrix.setIdentityM(mProjectionMatrix, 0);
   final float ratio = (float) width / height;
   final float left = -ratio;
   final float right = ratio;
   final float bottom = -1.0f;
   final float top = 1.0f;
   final float near = 1.0f;
   final float far = 100.0f;
   Matrix.frustumM(mProjectionMatrix, 0, left, right, bottom, top, near, far);

   Matrix.setLookAtM(mViewMatrix, 0, 0, 6, 2, 0, 0, -4, 0, 1, 0);

   drawBlock();
}

Here the drawBackground method:

private void drawBackground() {
   GLES20.glActiveTexture(GLES20.GL_TEXTURE0);
   GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, backgroundTextureHandle);
   GLES20.glUniform1i(mTextureUniformHandle, 0);

   Matrix.setIdentityM(mModelMatrix, 0);
   Matrix.setIdentityM(mProjectionMatrix, 0);

   mBackgroundPositions.position(0);
   GLES20.glVertexAttribPointer(mPositionHandle, POSITION_DATA_SIZE, GLES20.GL_FLOAT, 
      false, 0, mBackgroundPositions);
   GLES20.glEnableVertexAttribArray(mPositionHandle);

   mBackgroundColors.position(0);
   GLES20.glVertexAttribPointer(mColorHandle, COLOR_DATA_SIZE, GLES20.GL_FLOAT, false, 
      0, mBackgroundColors);
   GLES20.glEnableVertexAttribArray(mColorHandle);

   mBackgroundNormals.position(0);
   GLES20.glVertexAttribPointer(mNormalHandle, NORMAL_DATA_SIZE, GLES20.GL_FLOAT, 
      false, 0, mBackgroundNormals);
   GLES20.glEnableVertexAttribArray(mNormalHandle);

   mBackgroundTextureCoordinates.position(0);
   GLES20.glVertexAttribPointer(mTextureCoordinateHandle, TEXTURE_COORD_DATA_SIZE,   
      GLES20.GL_FLOAT, false, 0, mBackgroundTextureCoordinates);
   GLES20.glEnableVertexAttribArray(mTextureCoordinateHandle);

   // This multiplies the view matrix by the model matrix, and stores the result in the MVP matrix
   // (which currently contains model * view).
   Matrix.multiplyMM(mMVPMatrix, 0, mViewMatrix, 0, mModelMatrix, 0);

   // Pass in the modelview matrix.
   GLES20.glUniformMatrix4fv(mMVMatrixHandle, 1, false, mMVPMatrix, 0);

   // This multiplies the modelview matrix by the projection matrix, and stores the result in the MVP matrix
   // (which now contains model * view * projection).
   Matrix.multiplyMM(mMVPMatrix, 0, mProjectionMatrix, 0, mMVPMatrix, 0);

   // Pass in the combined matrix.
   GLES20.glUniformMatrix4fv(mMVPMatrixHandle, 1, false, mMVPMatrix, 0);

   // Pass in the light position in eye space.
   GLES20.glUniform3f(mLightPosHandle, mLightPosInEyeSpace[0], mLightPosInEyeSpace[1], 
      mLightPosInEyeSpace[2]);

   ShortBuffer buf = 
      ByteBuffer.allocateDirect(12).order(ByteOrder.nativeOrder()).asShortBuffer();
   buf.put(new short[] {0, 1, 2, 0, 2, 3});
   buf.position(0);

   // Draw the rectangle.
   GLES20.glDrawElements(GLES20.GL_TRIANGLES, 6, GLES20.GL_UNSIGNED_SHORT, buf);
   checkGlError("glDrawArrays");
 }

And finally the drawBlock method:

private void drawBlocks() {
   GLES20.glUseProgram(colorProgramHandle);
   checkGlError("glUseProgram");

   mMVPMatrixHandle = GLES20.glGetUniformLocation(colorProgramHandle, "uMVPMatrix");
   mMVMatrixHandle = GLES20.glGetUniformLocation(colorProgramHandle, "uMVMatrix");
   mLightPosHandle = GLES20.glGetUniformLocation(colorProgramHandle, "uLightPos");
   mTextureUniformHandle = GLES20.glGetUniformLocation(colorProgramHandle, "uTexture");

   mPositionHandle = GLES20.glGetAttribLocation(colorProgramHandle, "aPosition");
   mColorHandle = GLES20.glGetAttribLocation(colorProgramHandle, "aColor");
   mNormalHandle = GLES20.glGetAttribLocation(colorProgramHandle, "aNormal");
   mTextureCoordinateHandle = GLES20.glGetAttribLocation(colorProgramHandle, 
       "aTexCoordinate");

   Matrix.setIdentityM(mProjectionMatrix, 0);
   Matrix.setIdentityM(mModelMatrix, 0);

   blockMesh.vertexBuffer.position(0);
   GLES20.glVertexAttribPointer(mPositionHandle, POSITION_DATA_SIZE, GLES20.GL_FLOAT, 
      false, 0, blockMesh.vertexBuffer);
   GLES20.glEnableVertexAttribArray(mPositionHandle);

   blockMesh.colorBuffer.position(0);
   GLES20.glVertexAttribPointer(mColorHandle, COLOR_DATA_SIZE, GLES20.GL_FLOAT, false, 
      0, blockMesh.colorBuffer);
   GLES20.glEnableVertexAttribArray(mColorHandle);

   blockMesh.normalBuffer.position(0);
   GLES20.glVertexAttribPointer(mNormalHandle, NORMAL_DATA_SIZE, GLES20.GL_FLOAT, 
      false, 0, blockMesh.normalBuffer);
   GLES20.glEnableVertexAttribArray(mNormalHandle);

   // This multiplies the view matrix by the model matrix, and stores the result in the 
   MVP matrix
   // (which currently contains model * view).
   Matrix.multiplyMM(mMVPMatrix, 0, mViewMatrix, 0, mModelMatrix, 0);

   // Pass in the modelview matrix.
   GLES20.glUniformMatrix4fv(mMVMatrixHandle, 1, false, mMVPMatrix, 0);

   // This multiplies the modelview matrix by the projection matrix, and stores the 
   result in the MVP matrix
   // (which now contains model * view * projection).
   Matrix.multiplyMM(mMVPMatrix, 0, mProjectionMatrix, 0, mMVPMatrix, 0);

   // Pass in the combined matrix.
   GLES20.glUniformMatrix4fv(mMVPMatrixHandle, 1, false, mMVPMatrix, 0);

   // Pass in the light position in eye space.
   GLES20.glUniform3f(mLightPosHandle, mLightPosInEyeSpace[0], mLightPosInEyeSpace[1], 
      mLightPosInEyeSpace[2]);

   // Draw the cube.
   GLES20.glDrawElements(GLES20.GL_TRIANGLES, 36, GLES20.GL_UNSIGNED_SHORT, 
      blockMesh.indexBuffer);
   checkGlError("glDrawElements");
 }

I am not sure what I am missing about ortho and projection perspective. Any help is appreciated.

Answer 1

You’re wiping the projection matrix as part of drawBlocks. I don’t think you want to do that, if you want to draw it using the perspective projection already computed.

...
Matrix.setIdentityM(mProjectionMatrix, 0);   <-----
Matrix.setIdentityM(mModelMatrix, 0);

blockMesh.vertexBuffer.position(0);
...