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#version 150 core
uniform sampler2D distanceFieldTexture;
uniform float minAlpha;
uniform float maxAlpha;
uniform float textureSize;
uniform vec4 color;
in vec3 position;
in vec2 texCoord;
out vec4 fragColor;
void main()
{
// determine the scale of the glyph texture within pixel-space coordinates
// (that is, how many pixels are drawn for each texel)
vec2 texelDeltaX = abs(dFdx(texCoord));
vec2 texelDeltaY = abs(dFdy(texCoord));
float avgTexelDelta = textureSize * 0.5 * (texelDeltaX.x + texelDeltaX.y + texelDeltaY.x + texelDeltaY.y);
float texScale = 1.0 / avgTexelDelta;
// scaled to interval [0.0, 0.15]
float devScaleMin = 0.00;
float devScaleMax = 0.15;
float scaled = (clamp(texScale, devScaleMin, devScaleMax) - devScaleMin) / (devScaleMax - devScaleMin);
// thickness of glyphs should increase a lot for very small glyphs to make them readable
float base = 0.5;
float threshold = base * scaled;
float range = 0.06 / texScale;
float minAlpha = threshold - range;
float maxAlpha = threshold + range;
float distVal = texture(distanceFieldTexture, texCoord).r;
fragColor = color * smoothstep(minAlpha, maxAlpha, distVal);
}
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