fix LCD3x to match GBA / NDS screen

[GoogleCodeExporter]

Problem:
The current LCD3x is too saturated and bright for GBA games.
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Solution:
Change filter coeffs, decrase saturation and add contrast.

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changed filter coeffs (half of current values):

const float brighten_scanlines = 8.0;
const float brighten_lcd = 2.0;

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changed main function:

void main() {
vec2 angle = vTexCoord * omega;

float yfactor = (brighten_scanlines + sin(angle.y)) / (brighten_scanlines + 
1.0);
vec3 xfactors = (brighten_lcd + sin(angle.x + offsets)) / (brighten_lcd + 1.0);

const vec3 coef = vec3(0.299, 0.587, 0.114);
vec4 color = texture2D(rubyTexture, vTexCoord);
color = ((color-0.5)*1.1+0.5); /* adjust contrast to +10% */
vec3 gray = vec3(dot(color.rgb, coef));

gl_FragColor.rgb = yfactor * xfactors * vec3(mix(color.rgb, gray, 0.35)); /* 
-35% saturation*/
}

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Note:
Result may be different on every device. I compared side by side my NDS and my 
phone (Huawei Ascend P6) running MyBoy emulator and the colors match 
subjectively 95% with this change.

Original issue reported on code.google.com by adriano....@gmail.com on 16 Jul 2014 at 12:08