傲劍游戲工作室

这是我在国外的一个网站上看到的一篇文章,觉得很不错,以前我所知道的在Opengl中选择物体的方式有2种,一种是用Opengl自带的Select模式,一种是用包围盒来选择物体.这篇文章的方式是用一个唯一的Color ID来代表一个物体,然后根据这个Color来选择物体.DX也同样可以使用这样的方式.

实现的步骤:

• 关闭Opengl中的纹理,灯光和雾
• 使用物体定义的唯一Color来渲染这个物体
• 从后备缓冲数据中读出当前鼠标所在位置的颜色值
• 找出与读出的颜色值相匹配的物体

这种方法有个问题,在32Bit模式下是完全正确的,在16Bit下会因为颜色丢失的问题而选不中物体,解决方案在这篇文章里:http://www.3dkingdoms.com/selection.html

				
						源代码:
class BaseObject
{
private:
      unsignedchar m_colorID[3];
      staticunsignedchar gColorID[3];
  
 public:
      BaseObject()
      {
           m_colorID[0] = gColorID[0];
           m_colorID[1] = gColorID[1];
           m_colorID[2] = gColorID[2];
  
           gColorID[0]++;
           if(gColorID[0] > 255)
           {
                gColorID[0] = 0;
                gColorID[1]++;
                if(gColorID[1] > 255)
                {
                     gColorID[1] = 0;
                     gColorID[2]++;
                }
           }
      }
  
      ~BaseObject(){};
};

unsignedchar BaseObject::gColorID[3] = {0, 0, 0};


class SceneObject : public BaseObject
{
private:
      float m_position[3];
      string m_name;
  
 public:
      SceneObject();
      ~SceneObject();
  
      void Render();
      void Picking()
      {   // set mesh position
           glPushMatrix();
           glTranslatef(m_position[0], m_position[1], m_position[2]);
  
           glColor3f(m_colorID[0]/255.0f, m_colorID[1]/255.0f, m_colorID[2]/255.0f);
  
           // render object's vertices here
           glPopMatrix();
      }
};


void MouseDownEvent(int x, int y)
{  
      // turn off texturing, lighting and fog
      glDisable(GL_TEXTURE_2D);
      glDisable(GL_FOG);
      glDisable(GL_LIGHTING);
  
      // render every object in our scene// suppose every object is stored in a list container called SceneObjects
      list<SceneObject *>::iterator itr = SceneObjects.begin();
      while(itr != SceneObjects.end())
      {
           (*itr)->Picking();
           itr++;
      }


      // get color information from framebuffer




      unsignedchar pixel[3]; 
      GLint viewport[4];
      glGetIntegerv(GL_VIEWPORT, viewport);
       
      glReadPixels(x, viewport[3] - y, 1, 1, GL_RGB, GL_UNSIGNED_BYTE, pixel);
 
      // now our picked screen pixel color is stored in pixel[3]// so we search through our object list looking for the object that was selected
      itr = SceneObjects.begin();
      while(itr != SceneObjects.end())
      {
           if((*itr)->m_colorID[0] == pixel[0] && (*itr)->m_colorID[1] == pixel[1] && (*itr)->m_colorID[2] == pixel[2])
           {
                // flag object as selected
                SetSelected((*itr);
                break;
           }
           itr++;
      }
}









原文地址:http://gpwiki.org/index.php/OpenGL_Selection_Using_Unique_Color_IDs