openGL 选择和反馈（csGL）

• 画图形，定义模式为GL_SELECT，并为图形创建名字堆栈：

/// <summary>
        /// Draws the rectangles.
        /// </summary>
        /// <param name="mode">The selection mode.</param>
        private static void DrawRects(uint mode)
        {
            // The three rectangles are drawn.  In selection mode, each rectangle is given
            // the same name.  Note that each rectangle is drawn with a different z value.
            if (mode == GL_SELECT)
            {
                glLoadName(1);
            }
            glBegin(GL_QUADS);
            glColor3f(1.0f, 1.0f, 0.0f);
            glVertex3i(2, 0, 0);
            glVertex3i(2, 6, 0);
            glVertex3i(6, 6, 0);
            glVertex3i(6, 0, 0);
            glEnd();

            if (mode == GL_SELECT)
            {
                glLoadName(2);
            }
            glBegin(GL_QUADS);
            glColor3f(0.0f, 1.0f, 1.0f);
            glVertex3i(3, 2, -1);
            glVertex3i(3, 8, -1);
            glVertex3i(8, 8, -1);
            glVertex3i(8, 2, -1);
            glEnd();

            if (mode == GL_SELECT)
            {
                glLoadName(3);
            }
            glBegin(GL_QUADS);
            glColor3f(1.0f, 0.0f, 1.0f);
            glVertex3i(0, 2, -2);
            glVertex3i(0, 7, -2);
            glVertex3i(5, 7, -2);
            glVertex3i(5, 2, -2);
            glEnd();
        }

• 鼠标左键点击选中目标hit select:

        /// <summary>
        /// Updates pick selection.
        /// </summary>
        private static void PickRects()
        {
           private const int BUFSIZE = 512; // sets up selection mode, name stack,  and projection matrix for picking.  Then the objects are drawn
            uint[] selectBuf = new uint[BUFSIZE];
            int hits;
            int[] viewport = new int[4];

            glGetIntegerv(GL_VIEWPORT, viewport);

            glSelectBuffer(BUFSIZE, selectBuf);
            glRenderMode(GL_SELECT);

            glInitNames();
            glPushName(0);

            glMatrixMode(GL_PROJECTION);
            glPushMatrix();
            glLoadIdentity();
            // create 5x5 pixel picking region near cursor location
            gluPickMatrix((double)Model.Mouse.X, (double)(viewport[3] - Model.Mouse.Y), 5.0, 5.0, viewport);
            glOrtho(0.0f, 8.0f, 0.0f, 8.0f, -0.5f, 2.5f);
            DrawRects(GL_SELECT);
            glPopMatrix();
            glFlush();

            hits = glRenderMode(GL_RENDER);
            ProcessHits(hits, selectBuf);
        }
/// <summary>
        /// Displays hit data.
        /// </summary>
        /// <param name="hits">Number of hits.</param>
        /// <param name="buffer">The selection buffer.</param>
        private static void ProcessHits(int hits, uint[] buffer)
        {
            uint i, j;
            uint names;
            uint[] ptr;

            Console.WriteLine("hits = {0}", hits);
            ptr = buffer;
            for (i = 0; i < hits; i++)
            {                                                    // For Each Hit
                names = ptr[i];
                Console.WriteLine(" number of names for hit = {0}", names);
                i++;
                Console.WriteLine(" z1 is {0}", (float)ptr[i] / 0x7fffffff);
                i++;
                Console.WriteLine(" z2 is {0}", (float)ptr[i] / 0x7fffffff);
                i++;
                Console.Write(" the name is ");
                for (j = 0; j < names; j++)
                {                                            // For Each Name
                    Console.Write("{0} ", ptr[i]);
                    i++;
                }
                Console.Write("
");
            }
            Console.Write("
");
        }