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Rotating Cube Maps

Started by JonW Jul 11, 2003 at 9:58 AM 2 replies 450+ views

Original Post

Jul 11, 2003 at 9:58 AM

Hi, I''m using cube mapping to reflect the skybox on a water surface. It works OK, but the reflection rotates with the camera, so if there is a mountain behind the camera it will reflect in the water in front of the player, but if the camera rotates 90 degrees to the left, the mountain will still be reflected in front of it, instead of to the right of it. Here is my code:

//use cube environment mapping 
glPushMatrix();

	sky->getCubemap()->Bind();

	glTexGeni(GL_S, GL_TEXTURE_GEN_MODE, GL_REFLECTION_MAP_EXT);
	glTexGeni(GL_T, GL_TEXTURE_GEN_MODE, GL_REFLECTION_MAP_EXT);
	glTexGeni(GL_R, GL_TEXTURE_GEN_MODE, GL_REFLECTION_MAP_EXT);

	glMatrixMode(GL_TEXTURE);
	glPushMatrix();

		glEnable(GL_TEXTURE_CUBE_MAP_EXT);
		glEnable(GL_TEXTURE_GEN_S);
		glEnable(GL_TEXTURE_GEN_T);
		glEnable(GL_TEXTURE_GEN_R);
		glEnable(GL_NORMALIZE);

		drawHeightmap();

	glPopMatrix();
	glMatrixMode(GL_MODELVIEW);

glPopMatrix();

I believe I need to be rotating the texture matrix by the camera''s current rotation (I am using gluLookAt, so I''m not sure how to do this) after the second call to glPushMatrix. Its just a guess though. Any ideas? The water heightmap is rotating properly, its just the skybox reflection that won''t move. Thanks!

benjamin bunny

144

benjamin bunny

Jul 11, 2003 at 11:22 AM

You need to rotate the texture matrix by the inverse of your camera''s rotation.

JonW

Author

JonW

Jul 13, 2003 at 10:21 AM

Thanks!

How can I find the camera''s rotation if I am using gluLookAt? Maybe I have to pry it out of the modelview matrix?

JonW

Author

JonW

Jul 14, 2003 at 4:56 PM

Nevermind. I figured it out:


  GLfloat M[16]; 
  GLfloat T[16]; 
  glMatrixMode(GL_TEXTURE); 
  glGetFloatv( GL_TEXTURE_MATRIX, T );    
  glMatrixMode(GL_MODELVIEW); 
  glGetFloatv( GL_MODELVIEW_MATRIX, M ); 

  GLfloat U[3][3]; 
  GLfloat UInverse[3][3]; 

  U[0][0] = M[0]; 
  U[1][0] = M[1]; 
  U[2][0] = M[2]; 
  U[0][1] = M[4]; 
  U[1][1] = M[5]; 
  U[2][1] = M[6]; 
  U[0][2] = M[8]; 
  U[1][2] = M[9]; 
  U[2][2] = M[10]; 
 
  InvertMatrix(U, UInverse); 

  T[0]  = UInverse[0][0]; 
  T[1]  = UInverse[1][0]; 
  T[2]  = UInverse[2][0]; 
  T[4]  = UInverse[0][1]; 
  T[5]  = UInverse[1][1]; 
  T[6]  = UInverse[2][1]; 
  T[8]  = UInverse[0][2]; 
  T[9]  = UInverse[1][2]; 
  T[10] = UInverse[2][2]; 
  
  glMatrixMode(GL_TEXTURE); 

  glLoadMatrixf( T );

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