FreeTypeGL-0.0.1: shaders/distance-field.frag

/* =========================================================================
 * Freetype GL - A C OpenGL Freetype engine
 * Platform:    Any
 * WWW:         http://code.google.com/p/freetype-gl/
 * -------------------------------------------------------------------------
 * Copyright 2011 Nicolas P. Rougier. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 *  1. Redistributions of source code must retain the above copyright notice,
 *     this list of conditions and the following disclaimer.
 *
 *  2. Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY NICOLAS P. ROUGIER ''AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO
 * EVENT SHALL NICOLAS P. ROUGIER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
 * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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 * The views and conclusions contained in the software and documentation are
 * those of the authors and should not be interpreted as representing official
 * policies, either expressed or implied, of Nicolas P. Rougier.
 * ========================================================================= */
uniform sampler2D texture;
       vec3 glyph_color    = vec3(1.0,1.0,1.0);
const float glyph_center   = 0.50;
       vec3 outline_color  = vec3(0.0,0.0,0.0);
const float outline_center = 0.55;
       vec3 glow_color     = vec3(1.0,1.0,1.0);
const float glow_center    = 1.25;
void main(void)
{
    vec4  color = texture2D(texture, gl_TexCoord[0].st);
    float dist  = color.a;
    float width = fwidth(dist);
    float alpha = smoothstep(glyph_center-width, glyph_center+width, dist);

    // Smooth
    // gl_FragColor = vec4(glyph_color, alpha);

    // Outline
    // float mu = smoothstep(outline_center-width, outline_center+width, dist);
    // vec3 rgb = mix(outline_color, glyph_color, mu);
    // gl_FragColor = vec4(rgb, max(alpha,mu));

    // Glow
    //vec3 rgb = mix(glow_color, glyph_color, alpha);
    //float mu = smoothstep(glyph_center, glow_center, sqrt(dist));
    //gl_FragColor = vec4(rgb, max(alpha,mu));

    // Glow + outline
    vec3 rgb = mix(glow_color, glyph_color, alpha);
    float mu = smoothstep(glyph_center, glow_center, sqrt(dist));
    color = vec4(rgb, max(alpha,mu));
    float beta = smoothstep(outline_center-width, outline_center+width, dist);
    rgb = mix(outline_color, color.rgb, beta);
    gl_FragColor = vec4(rgb, max(color.a,beta));

}