sharp_bilinear+natural_vision.dsd

// sharp_bilinear+natural_vision - This is an integer prescale filter that
// should be combined with bilinear hardware filtering (GL_LINEAR filter
// or some such) to achieve a smooth scaling result with minimum blur. This
// is good for pixel graphics that are scaled by non-integer factors. Also
// applies 'Natural Vision' colour enhancement
// 
// - Original 'sharp_bilinear' code copyright (C) rsn8887 & TheMaister and
//   released into the public domain
// 
// - Original 'natural_vision' code written by ShadX, modified by
//   Hyllian and Sp00kyFox, released into the public domain
// 
// 'Ported' (i.e. copy/paste) to DraStic format by jdgleaver
// 
// 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.
=============================================

<vertex>

attribute vec2 a_vertex_coordinate;
attribute vec2 a_texture_coordinate;

uniform vec4 u_texture_size;
uniform vec2 u_target_size;

varying vec2 precalc_texel;
varying vec2 precalc_scale;

void main()
{
	gl_Position = vec4(a_vertex_coordinate.xy, 0.0, 1.0);
	
	precalc_texel = a_texture_coordinate * u_texture_size.zw;
	precalc_scale = floor(u_target_size.xy / u_texture_size.zw) + 1.0;
}

</vertex>

<fragment>

#ifndef NATVIS_GIN
#define NATVIS_GIN 1.91
#endif
#ifndef NATVIS_GOUT
#define NATVIS_GOUT 1.91
#endif
#ifndef NATVIS_Y
#define NATVIS_Y 1.1
#endif
#ifndef NATVIS_I
#define NATVIS_I 1.1
#endif
#ifndef NATVIS_Q
#define NATVIS_Q 1.1
#endif

uniform sampler2D u_texture;

uniform vec4 u_texture_size;
uniform vec2 u_target_size;

varying vec2 precalc_texel;
varying vec2 precalc_scale;

// Natural Vision helpers
const mat3 RGBtoYIQ = mat3(0.299,  0.595716,  0.211456, 
									0.587, -0.274453, -0.522591, 
									0.114, -0.321263,  0.311135);

const mat3 YIQtoRGB = mat3(1.0, 1.0, 1.0,
									0.95629572,-0.27212210,-1.10698902,
									0.62102442,-0.64738060, 1.70461500);

const vec3 YIQ_lo = vec3(0.0, -0.595716, -0.522591);
const vec3 YIQ_hi = vec3(1.0,  0.595716,  0.522591);

void main()
{
	vec2 texel_floored = floor(precalc_texel);
	vec2 s = fract(precalc_texel);
	vec2 region_range = 0.5 - 0.5 / precalc_scale;
	
	// Figure out where in the texel to sample to get correct pre-scaled bilinear.
	// Uses the hardware bilinear interpolator to avoid having to sample 4 times manually.
	
	vec2 center_dist = s - 0.5;
	vec2 f = (center_dist - clamp(center_dist, -region_range, region_range)) * precalc_scale + 0.5;
	
	vec2 mod_texel = texel_floored + f;
	
	// Get colour sample and apply colour enhancement
	vec3 colour = pow(texture2D(u_texture, mod_texel / u_texture_size.zw).rgb, vec3(NATVIS_GIN));
	colour = RGBtoYIQ * colour;
	colour = vec3(pow(colour.x, NATVIS_Y), colour.y * NATVIS_I, colour.z * NATVIS_Q);
	colour = clamp(colour, YIQ_lo, YIQ_hi);
	colour = YIQtoRGB * colour;
	colour = pow(colour, vec3(1.0 / NATVIS_GOUT));
	
	gl_FragColor = vec4(colour.rgb, 1.0);
}

</fragment>