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 Readme for:  Document » Tutorial » fading_tut.lha


Description: An SDL tutorial on Fading for Varthall :)
Download: fading_tut.lha       (TIPS: Use the right click menu if your browser takes you back here all the time)
Size: 181kb
Version: 3
Date: 24 Sep 2006
Author: Patrick Kooman, AmigaOS 4.0 compile by Spot / Up Rough
Submitter: Spot / Up Rough
Email: spot/triad se
Homepage: http://www.2dgame-tutorial.com/sdl/index.htm
Requirements: SDL
Category: document/tutorial
License: Other
Distribute: yes
Min OS Version: 4.0
FileID: 2110
Comments: 1
Snapshots: 0
Videos: 0
Downloads: 362  (Current version)
362  (Accumulated)
Votes: 0 (0/0)  (30 days/7 days)

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Notes from Spot. Hi Varthall, I found what you need to finish that port.


This little page is about fading. It describes the technique which slowly lets
an image appear or disappear from the screen. A split-off from the "appear"
techique is called a cross-fade. Most people (including myself) like these
tricks because it looks so cool.

The regular apprauch is that each frame during a fade, all RGB values of the
pixels get modified by a certain amount, which makes the screen become darker or
brighter (depends on the fade-option).

There are two disadvantages to this apprauch:
Pixel-operations are slow, especcialy when done in video memory
Pixel-operations depend on the bit depth. Each bit-dept (8, 15/16, 24, 32) needs
it's own implementation
In this page, I'd like to show another way to make a fade. (I explain it for
fading out, but for fading in it's just the other way around.) Alphablending. In
stead of making the screen-surface darker, we go blend a black surface over it.
If we slowly increase the aplha value from 0 (not visible ) to 255 (fully
visible), the screen seems to get darker and darker, simulating a fade-out.

When this technique is beeing used on a modern videocard, where alphablending is
hardware accelerated, you have the fade almost for free, and for each bit-dept.

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