title: glOrtho OpenGL es 2.0 variant how fix blank screen?
body: <p>I try to remake a OpenGL ES 2.0 example for Android <a href="http://developer.android.com/resources/tutorials/opengl/opengl-es20.html" rel="nofollow">http://developer.android.com/resources/tutorials/opengl/opengl-es20.html</a>
  to Android NDK OpenGL ES 2.0 example.<br></p>
  
  <p>I succeded in all except making a orthographic/perspective projection</p>
  
  <p>So i draw a triangle</p>
  
  <pre><code>typedef matrix float matrix[16];
  
  matrix MVP_MATRIX; /* MODEL*VIEW*PROJECTION MATRIX */
  matrix PROJECTION_MATRIX;
  matrix MODEL_MATRIX;
  matrix VIEW_MATRIX;
  
  s_shader shader; /* just struct for holding shader program data (attribytes,uniforms, fragment shader, vertex shader etc)*/
  
  GLfloat triangle_vertices[] =
                   {
                    0.0f, 0.5f, 0.0f,
                   -0.5f, -0.5f, 0.0f,
                    0.5f, -0.5f, 0.0f
                   };
  
     onInit(float screen_width, float screen_height)
     {
     /*shader load*/
     matrix MV_MATRIX;
     identity_matrix(MODEL_MATRIX); //any transitions/rotations works fine
     identity_matrix(VIEW_MATRIX);
     multiply_matrix(VIEW_MATRIX, MODEL_MATRIX, MV_MATRIX);
     glViewport(0, 0, screen_width, screen_height);
     ortho_matrix(0.0,screen_width,0.0,screen_height,1.0,10.0, PROJECTION_MATRIX);
     multiply_matrix(MV_MATRIX, PROJECTION_MATRIX , MVP_MATRIX);
     }
  
  
    onDraw()
    {
    glClear(GL_COLOR_BUFFER_BIT);
    glUseProgram(shader.program /* where i hold a compiled shader program */ );
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, triangle_vertices);
    glUniformMatrix4fv(shader.uniforms[0]/*"umWorld" uniform location*/, 1,   GL_FALSE, (const GLfloat*) MVP_MATRIX/*Well get blank screen, if change to MV_MATRIX everything is fine, so projection matrix is problem*/);
    glEnableVertexAttribArray(shader.atributes[0]/*"vPosition" attribute location*/);
    glDrawArrays(GL_TRIANGLES, 0, 3);
    }
  
  void ortho_matrix(float left, float right, float bottom, float top, float near,
  float  far, matrix result)
  {
  result[0] = 2.0 / (right - left);
  result[1] = 0.0;
  result[2] = 0.0;
  result[3] = 0.0;
  
  //Second Column
  result[4] = 0.0;
  result[5] = 2.0 / (top - bottom);
  result[6] = 0.0;
  result[7] = 0.0;
  
  //Third Column
  result[8] = 0.0;
  result[9] = 0.0;
  result[10] = -2.0 / (far - near);
  result[11] = 0.0;
  
  //Fourth Column
  result[12] = -(right + left) / (right - left);
  result[13] = -(top + bottom) / (top - bottom);
  result[14] = -(far + near) / (far - near);
  result[15] = 1;
  }
  </code></pre>
  
  <p>Vertex shader</p>
  
  <pre><code>attribute vec4 vPosition;
  uniform mat4 umWorld;
  void main()
  {
  gl_Position = umWorld * vPosition; 
  } 
  </code></pre>
  
  <p>Fragment shader</p>
  
  <pre><code>precision lowp float;
  void main()
  {
  gl_FragColor = vec4(1.0,0.0,1.0,1.0);
  }
  </code></pre>
  
  <p>P.S. i think i pass wrong things to ortho_matrix, cos opengl es has (-1,-1,-1) - (1,1,1) coordinate system.</p>