выбор цвета glkit в opengl iOS

Речь идет о выборе 3D-объекта с помощью выбора цвета. Я рисую свою сетку (обновление: которая находится в статическом заголовочном файле и отлично отображается на экране в том же проекте) в новый закадровый буфер кадра, а затем я использую glReadPixels, чтобы определить, коснулся ли ее пользователь.

Следуя коду из проекта opengles_ch10_1 из книги Эрика М. Бака «Изучение OpenGLES для iOS», я написал следующий код, который всегда выводит в nslog цвет 0,0,0 для выбранного (нажатием) пикселя.

Мой код:

- (IBAction) tapGesture:(id)sender
{
   if ([(UITapGestureRecognizer *)sender state] == UIGestureRecognizerStateEnded) {

       CGPoint tapLocation = [(UITapGestureRecognizer *)sender locationInView:self.view];

        int tt = [self findMeshByPoint:tapLocation];

        //NSLog( @"tap value: %i", tt );
    }
}

- (NSUInteger)findMeshByPoint:(CGPoint)point
{
    //In openGL the y axis starts from the bottom of the screen

    point.y = self.view.bounds.size.height - point.y;

    GLKView *glView = (GLKView *)self.view;

    NSAssert([glView isKindOfClass:[GLKView class]],
             @"View controller's view is not a GLKView");

    // Make the view's context current

    [EAGLContext setCurrentContext:glView.context];

    glBindVertexArrayOES(0);

//        self.effect.constantColor = GLKVector4Make( 1.0f,  //This should be meshId/255.0f

    if(0 == _glVertexAttributeBufferID)
    {
        GLuint  glName;

        glGenBuffers(1,                // STEP 1

                     &glName);

        glBindBuffer(GL_ARRAY_BUFFER,  // STEP 2
                     glName);

        glBufferData(                  // STEP 3

                     GL_ARRAY_BUFFER,  // Initialize buffer contents

                    sizeof(parparit51OBJVertices), parparit51OBJVertices,

                     GL_STATIC_DRAW);            // Hint: cache in GPU memory

        _glVertexAttributeBufferID = glName;

    }
    else
    {
        glBindBuffer(GL_ARRAY_BUFFER,

                     _glVertexAttributeBufferID);
    }

    //glEnableVertexAttribArray(TETerrainPositionAttrib);

    glEnableVertexAttribArray( GLKVertexAttribPosition );

     if(0 == _program)
     {
            [self loadShadersWithName:@"UtilityPickTerrainShader"];

            [self buildFBO];

            NSAssert(0 != _program,

                     @"prepareOpenGL failed to load shaders");
        }

        glUseProgram(_program);

        // Pre-calculate the mvpMatrix

        GLKMatrix4 modelViewProjectionMatrix2 =

        GLKMatrix4Multiply(

                           self.effect.transform.projectionMatrix,

                           self.effect.transform.modelviewMatrix);

        // Standard matrices

        glUniformMatrix4fv(uniforms[UtilityPickTerrainMVPMatrix], 1, 0,

                           modelViewProjectionMatrix2.m);

//        glUniform2fv(uniforms[UtilityPickTerrainDimensionFactors], 1,

//                     &_temp1 ); //self.factors.v);  //I removed this from the shaders

        glUniform1f(uniforms[UtilityPickTerrainModelIndex],

                    1.0f ); // self.modelIndex / 255.0f);

    glBindFramebuffer(GL_FRAMEBUFFER, _pickFBO);

    glViewport(0, 0, 512, 512);

    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    //glEnableVertexAttribArray(GLKVertexAttribPosition);

    glVertexAttribPointer(GLKVertexAttribPosition, 3, GL_FLOAT, GL_FALSE, 12 * sizeof(GLfloat), 0);

    NSLog( @"******* 7" );

    [self.effect prepareToDraw];

    glDrawArrays(GL_TRIANGLES, 0, sizeof(parparit51OBJVertices) / sizeof(Vertex));

    NSLog( @"******* 7.5" );

    const GLfloat width = [glView drawableWidth];

    const GLfloat height = [glView drawableHeight];

    NSAssert(0 < width && 0 < height, @"Invalid drawble size");

    // Get info for picked location

    const GLKVector2 scaledProjectionPosition = {

        point.x / width,

        point.y / height

    };

    NSLog( @"******* 8" );

    GLubyte pixelColor[4];  // Red, Green, Blue, Alpha color

    GLint readLocationX = MIN((512 - 1),

                              (512 - 1) * scaledProjectionPosition.x);

    GLint readLocationY = MIN((512 - 1),

                              (512 - 1) * scaledProjectionPosition.y);

    glReadPixels(readLocationX,

                 readLocationY,

                 1,

                 1,

                 GL_RGBA,

                 GL_UNSIGNED_BYTE,

                 pixelColor);


    NSLog(@"pixelColor[0]=%i, pixelColor[1]=%i, pixelColor[2]=%i", pixelColor[0], pixelColor[1], pixelColor[2] );


    // Restore OpenGL state that pickTerrainEffect changed

    glBindFramebuffer(GL_FRAMEBUFFER, 0); // default frame buffer

    glViewport(0, 0, width, height); // full area of glView

    return 0;

}

-(void) buildFBO
{
    if ( 0 == _pickFBO )
    {

        GLuint colorTexture;

        // Create a texture object to apply to model

        glGenTextures(1, &colorTexture);

        glBindTexture(GL_TEXTURE_2D, colorTexture);

        // Set up filter and wrap modes for this texture object

        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S,
                        GL_CLAMP_TO_EDGE);

        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T,
                        GL_CLAMP_TO_EDGE);

        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER,
                        GL_LINEAR);

        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER,
                        GL_LINEAR_MIPMAP_LINEAR);

        // Allocate a texture image we can render into

        // Pass NULL for the data parameter since we don't need to

        // load image data. We will be generating the image by

        // rendering to this texture.

        glTexImage2D(GL_TEXTURE_2D,

                     0,

                     GL_RGBA,

                     512,

                     512,

                     0,

                     GL_RGBA,

                     GL_UNSIGNED_BYTE,

                     NULL);

        GLuint depthRenderbuffer;

        glGenRenderbuffers(1, &depthRenderbuffer);

        glBindRenderbuffer(GL_RENDERBUFFER, depthRenderbuffer);

        glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT16,

                              512, 512);

        glGenFramebuffers(1, &_pickFBO);

        glBindFramebuffer(GL_FRAMEBUFFER, _pickFBO);

        glFramebufferTexture2D(GL_FRAMEBUFFER,

                               GL_COLOR_ATTACHMENT0,

                               GL_TEXTURE_2D, colorTexture, 0);

        glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, depthRenderbuffer);

        if(glCheckFramebufferStatus(GL_FRAMEBUFFER) !=

           GL_FRAMEBUFFER_COMPLETE)
        {
            NSLog(@"failed to make complete framebuffer object %x", glCheckFramebufferStatus(GL_FRAMEBUFFER));

            //+++tbd+++UtilityPickTerrainEffectDestroyFBO(fboName);

            return;
        }

        //#ifdef DEBUG
        //    {  // Report any errors
        GLenum error = glGetError();

        if(GL_NO_ERROR != error)
        {

            NSLog(@"GL Error: 0x%x", error);

        }
        //    }
        //#endif
    }
}