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Channel Shuffle Effect

I) Introduction

Dear PCSX2 users,

GSdx got various improvements recently, issues were fixed on games such as Metal Gear Solid 3, Gran Turismo 4, Tekken 5, Tales of Legendia and Urban Chaos. All of those games use a certain effect that I have nicknamed as the "Channel Shuffle Effect". All games use a variation of this effect but each time the effect proved to be memory expensive and it was very slow, even with the best computers. The effect is very interesting because it explains the rendering/GPU architecture evolution from a fixed unit to a processor. So I decided to take this opportunity to explain it the best I can.


Read more: Channel Shuffle Effect


Explanation of impossible blend

The goal of blending is to combine two colors. The general equation on a modern GPU is:



coefficient1 * color1 +/- coefficient2 * color2

Color1/Color 2 are either the source color or the destination color.
Coefficient1/Coefficient2 are either the alpha value (transparency) of source/source2/destination, 1 - alpha, or a constant. The GPU will clamp the coefficients to [0;1]

The general equation on the PS2 however is:



(Color1 - Color2) * Coefficient + Color3

Color1/Color2/Color3 are either the source or destination color or zero.

Coefficient is the alpha value (transparency) of the source or destination, or a constant.

Read more: Explanation of impossible blend


Explanation of why hacks are needed to fix upscaling related glitches

First, let's explain aliasing and why people are so keen on removing it with anti-aliasing. Let's start with some math Smile

In the real world, signals are often "continuous." If you take two points A and B and A is very close to B then F(A) is very close to F(B). But a screen is not continuous. If you take two pixels side by side, one can be white while the other is black.

Read more: Explanation of why hacks are needed to fix upscaling related glitches


MMU mini-series part 2 of 4

Hello PCSX2 followers,

After a long delay, this is the second part of the MMU mini-presentation. In the previous chapter we saw that MMU allows giving a virtual address space to a process. Besides, I told you MMU controls the cache behavior (cacheable/uncached accelerated/uncached). First, let me quickly explain the different cache accesses. Then I will introduce the default memory mapping of the PS2.

Read more: MMU mini-series part 2 of 4


MMU mini-series

Hello PCSX2 followers,

It's been a while since the last developer blog entry. I would like to resume this old tradition.

I will present you a mini series on the MMU (memory management unit) and virtual memory. Jake and ZeroFrog already wrote some posts relating to this topic:

This time, I will explain the goal of MMU and why it is mandatory for modern systems. The MMU is a cornerstone for stability and security. I will also explain why it could be costly for the performance on the native system.

On the next article, I will present you the PS2 address space and how the MMU is really used.

Read more: MMU mini-series

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