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uniform highp mat4 mvp;
uniform highp float fontScale;
uniform int textureWidth;
uniform int textureHeight;
attribute highp vec4 vCoord;
attribute highp vec2 tCoord;
varying highp vec2 sampleCoord;
varying highp vec2 alphas;
highp float thresholdFunc(highp float scale)
{
highp float base = 0.5;
highp float baseDev = 0.065;
highp float devScaleMin = 0.15;
highp float devScaleMax = 0.3;
return base - ((clamp(scale, devScaleMin, devScaleMax) - devScaleMin) / (devScaleMax - devScaleMin) * -baseDev + baseDev);
}
highp float spreadFunc(highp float scale)
{
return 0.06 / scale;
}
highp vec2 alphaRange(highp float scale)
{
highp float base = thresholdFunc(scale);
highp float range = spreadFunc(scale);
highp float alphaMin = max(0.0, base - range);
highp float alphaMax = min(base + range, 1.0);
return vec2(alphaMin, alphaMax);
}
highp float determinantOfSubmatrix(highp mat4 m, int col0, int col1, int row0, int row1)
{
return m[col0][row0] * m[col1][row1] - m[col0][row1] * m[col1][row0];
}
highp float determinantOfSubmatrix(highp mat4 m, int col0, int col1, int col2, int row0, int row1, int row2)
{
highp float det = m[col0][row0] * determinantOfSubmatrix(m, col1, col2, row1, row2);
det -= m[col1][row0] * determinantOfSubmatrix(m, col0, col2, row1, row2);
det += m[col2][row0] * determinantOfSubmatrix(m, col0, col1, row1, row2);
return det;
}
highp float determinant(highp mat4 m)
{
highp float det = m[0][0] * determinantOfSubmatrix(m, 1, 2, 3, 1, 2, 3);
det -= m[1][0] * determinantOfSubmatrix(m, 0, 2, 3, 1, 2, 3);
det += m[2][0] * determinantOfSubmatrix(m, 0, 1, 3, 1, 2, 3);
det -= m[3][0] * determinantOfSubmatrix(m, 0, 1, 2, 1, 2, 3);
return det;
}
void main()
{
highp float scale = fontScale * sqrt(abs(determinant(mvp)));
alphas = alphaRange(scale);
sampleCoord = tCoord * vec2(1.0 / float(textureWidth), 1.0 / float(textureHeight));
gl_Position = mvp * vCoord;
}
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