Implementing object picking using color

Another method which is used for picking objects in a 3D world is color-based picking. In this recipe, we will use the same scene as in the last recipe.

Getting ready

The code for this recipe is in the Chapter2/Picking_ColorBuffer folder. Relevant source files are in the Chapter2/src folder.

How to do it…

To enable picking with the color buffer, the following steps are needed:

1. Disable dithering. This is done to prevent any color mismatch during the query:

   glDisable(GL_DITHER);

2. In the mouse down event handler, read the color value at the clicked position from the color buffer using the glReadPixels function:

   GLubyte pixel[4];
   glReadPixels(x, HEIGHT-y, 1, 1, GL_RGBA, GL_UNSIGNED_BYTE, pixel);

3. Compare the color value at the clicked point to the color values of all objects to find the intersection:

   selected_box=-1;
   if(pixel[0]==255 && pixel[1]==0 && pixel[2]==0) {
     cout<<"picked box 1"<<endl;
     selected_box = 0;
   }
   if(pixel[0]==0 &amp...