Jump to content
  • Advertisement


This topic is now archived and is closed to further replies.


Need some help understanding Lesson 9

This topic is 5560 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

If you intended to correct an error in the post then please contact us.

Recommended Posts

Hi, I''m having some trouble getting to grips and understanding some code in lesson 9. I assume this is what you call billboarding for particles. in his DrawGLScene function. he does the following:
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);	// Clear The Screen And The Depth Buffer

	glBindTexture(GL_TEXTURE_2D, texture[0]);		// Select Our Texture

	for (loop=0; loop<num; loop++)				// Loop Through All The Stars

		glLoadIdentity();				// Reset The View Before We Draw Each Star

		glTranslatef(0.0f,0.0f,zoom);			// Zoom Into The Screen (Using The Value In ''zoom'')

		glRotatef(tilt,1.0f,0.0f,0.0f);			// Tilt The View (Using The Value In ''tilt'')

glRotatef(star[loop].angle,0.0f,1.0f,0.0f);	// Rotate To The Current Stars Angle

		glTranslatef(star[loop].dist,0.0f,0.0f);	// Move Forward On The X Plane

glRotatef(-star[loop].angle,0.0f,1.0f,0.0f);	// Cancel The Current Stars Angle

		glRotatef(-tilt,1.0f,0.0f,0.0f);		// Cancel The Screen Tilt

Wouldn''t cancelling out the tilt and rotation effectively produce a null effect and rotating the screen would be useless? If someone could explain this to me in different terms please, I would appreciate it.

Share this post

Link to post
Share on other sites
Guest Anonymous Poster

You have to remember that those rotation commands are going to affect the translate command. If there were no rotate calls first then making a translation would put the star wherever the translate command specified, but with rotation calls first(assuming the angle rotated isn''t 0) the star will be translated in the direction that is the combined result of the rotations and translation. After the star has been translated, the "unrotation" commands will just make sure that the star is now facing the proper orientation towards the viewer.

Share this post

Link to post
Share on other sites

  • Advertisement

Important Information

By using GameDev.net, you agree to our community Guidelines, Terms of Use, and Privacy Policy.

We are the game development community.

Whether you are an indie, hobbyist, AAA developer, or just trying to learn, GameDev.net is the place for you to learn, share, and connect with the games industry. Learn more About Us or sign up!

Sign me up!