overte-HifiExperiments/libraries/render-utils/src/sdf_text3D_transparent.slf

<@include gpu/Config.slh@>
<$VERSION_HEADER$>
//  Generated on <$_SCRIBE_DATE$>
//  sdf_text3D_transparent.frag
//  fragment shader
//
//  Created by Bradley Austin Davis on 2015-02-04
//  Based on fragment shader code from 
//  https://github.com/paulhoux/Cinder-Samples/blob/master/TextRendering/include/text/Text.cpp 
//  Distributed under the Apache License, Version 2.0.
//  See the accompanying file LICENSE or http://www.apache.org/licenses/LICENSE-2.0.html

<@include DeferredBufferWrite.slh@>
<@include render-utils/ShaderConstants.h@>

LAYOUT(binding=0) uniform sampler2D Font;

struct TextParams {
    vec4 color;
    vec4 outline;
};

LAYOUT(binding=0) uniform textParamsBuffer {
    TextParams params;
};

// the interpolated normal
layout(location=RENDER_UTILS_ATTR_NORMAL_WS) in vec3 _normalWS;
layout(location=RENDER_UTILS_ATTR_TEXCOORD01) in vec4 _texCoord01;
#define _texCoord0 _texCoord01.xy
#define _texCoord1 _texCoord01.zw

#define TAA_TEXTURE_LOD_BIAS    -3.0

const float interiorCutoff = 0.8;
const float outlineExpansion = 0.2;
const float taaBias = pow(2.0, TAA_TEXTURE_LOD_BIAS);

float evalSDF(vec2 texCoord) {
    // retrieve signed distance
    float sdf = textureLod(Font, texCoord, TAA_TEXTURE_LOD_BIAS).g;
    sdf = mix(sdf, mix(sdf + outlineExpansion, 1.0 - sdf, float(sdf > interiorCutoff)), float(params.outline.x > 0.0));

    // Rely on TAA for anti-aliasing
    return step(0.5, sdf);
}

void main() {
    vec2 dxTexCoord = dFdx(_texCoord0) * 0.5 * taaBias;
    vec2 dyTexCoord = dFdy(_texCoord0) * 0.5 * taaBias;

    // Perform 4x supersampling for anisotropic filtering
    float a;
    a = evalSDF(_texCoord0);
    a += evalSDF(_texCoord0 + dxTexCoord);
    a += evalSDF(_texCoord0 + dyTexCoord);
    a += evalSDF(_texCoord0 + dxTexCoord + dyTexCoord);
    a *= 0.25;

    packDeferredFragmentTranslucent(
        normalize(_normalWS),
        a * params.color.a,
        params.color.rgb,
        DEFAULT_ROUGHNESS);
}