Retro Shader

/*
   Hyllian - Retro Shader - 2013

   A re-implementation from the original made by Hyllian and DOLLS!

   This program is free software; you can redistribute it and/or
   modify it under the terms of the GNU General Public License
   as published by the Free Software Foundation; either version 2
   of the License, or (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.

*/

/*
	VERTEX_SHADER
*/
void main_vertex
(
	float4 position	: POSITION,
	float4 color	: COLOR,
	float2 texCoord : TEXCOORD0,

	uniform float4x4 modelViewProj,

	out float4 oPosition	: POSITION,
	out float4 oColor	: COLOR,
	out float2 otexCoord	: TEXCOORD
)
{
	oPosition = mul(modelViewProj, position);
	oColor = color;
	otexCoord = texCoord;
}

/*
	FRAGMENT SHADER
*/



struct output
{
	float4 color	: COLOR;
};

struct input
{
	float2 video_size;
	float2 texture_size;
	float2 output_size;
};

// This value must be between 0.0 (totally black) and 1.0 (nearest neighbor)
#define PIXEL_SIZE  0.84

output main_fragment(float2 texCoord: TEXCOORD0, uniform sampler2D decal : TEXUNIT0, uniform input IN)
{
    // Reading the texel
    float3 E = pow(tex2D(decal, texCoord).xyz, float3(2.4));

    float2 fp = frac(texCoord*IN.texture_size);
    float2 ps = IN.video_size/IN.output_size;

    float2 f = clamp(clamp(fp + 0.5*ps, 0.0, 1.0) - PIXEL_SIZE, 0.0, ps)/ps;

    float max_coord = max(f.x, f.y);

    float3 res = lerp(E*(1.04+fp.x*fp.y), E*0.36, max_coord);

    // Product interpolation
    output OUT;
    OUT.color = float4(clamp( pow(res, float3(1.0 / 2.2)), 0.0, 1.0 ), 1.0);
    return OUT;
}