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# PARALLAX SCROLLING

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Does anyone knows any good tutorial or book on Parallax scrolling (or any other scrolling techniques)? And about 2D scrolling in OPENGL?

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Parallax scrolling is fairly easy. If you can make a single layer scroll your already half way there.

So let''s do it like this 3 layers.

Background Layer
Middle Layer
Foreground Layer.

Now let''s say your player moves at a velocity of 3. This means that if your player is moving that you probably want to scroll your foreground layer at a velocity of 3 also.

Now what parallax introduces is the faking of 3d in a 2d world. When in the passengers seat of a car, driving down the highway the closer things are to you the faster they move.

So in order to do this with our layers. We take the velocity of the foreground layer (3 in our case). And we reduce it for the middle layer. In this case I want to take the speed of the foreground layer and reduce it by 25%. 3 * .25 = .75 so 3 - 0.75 = 2.25. 2.25 is the new velocity for our middle layer.
Finaly the background layer. We take our middle layers velocity and reduce that by 25%. 2.25 * .25 = .5625 so 2.25 - .5625 = 1.6875. Or rounded up to 1.7. So 1.7 is our new background layers velocity.

So now what do you do?

Well check if the player is moving. If he''s moving right, increase the foreground position by it''s velocity which is 3, the middle layers position by it''s velocity which is 2.25, and the backgrounds position by it''s velocity which is 1.7.

If he;s moving left, you decrease the position by the velocity and bam! you''ve got parallax scrolling.

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Wow, thanks evaclear. I''ll give it a try.

Do you know opengl? So in order to do this in opengl, i''d use
something like glRasterPos21 an GlBitmap, or GLDrawPixels, right?

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