sharp_bilinear.dsd

// sharp_bilinear - 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.
// 
// Original code copyright (C) rsn8887 & TheMaister and 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>

uniform sampler2D u_texture;

uniform vec4 u_texture_size;
uniform vec2 u_target_size;

varying vec2 precalc_texel;
varying vec2 precalc_scale;

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;
	
	vec3 colour = texture2D(u_texture, mod_texel / u_texture_size.zw).rgb;
	
	gl_FragColor = vec4(colour.rgb, 1.0);
}

</fragment>