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Use dichotomic algorithm to converge to new Alpha

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brunoherbelin
2021-02-28 10:18:42 +01:00
parent f2cd18f754
commit 13672a9d01
1 changed files with 16 additions and 13 deletions
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29
Source.cpp
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@@ -445,15 +445,19 @@ void Source::setLocked (bool on)
}
// Transfer functions from coordinates to alpha (1 - transparency)
// linear distance
float linear_(float x, float y) {
return 1.f - CLAMP( sqrt( ( x * x ) + ( y * y ) ), 0.f, 1.f );
}
// quadratic distance
float quad_(float x, float y) {
return 1.f - CLAMP( ( x * x ) + ( y * y ), 0.f, 1.f );
}
float sin_quad(float x, float y) {
// best alpha transfer function: quadratic sinusoidal shape
float sin_quad_(float x, float y) {
float D = sqrt( ( x * x ) + ( y * y ) );
return 0.5f + 0.5f * cos( M_PI * CLAMP( D * sqrt(D), 0.f, 1.f ) );
// return 0.5f + 0.5f * cos( M_PI * CLAMP( ( ( x * x ) + ( y * y ) ), 0.f, 1.f ) );
@@ -478,20 +482,19 @@ float Source::alpha() const
void Source::setAlpha(float a)
{
// todo clamp a
glm::vec2 dist = glm::vec2(groups_[View::MIXING]->translation_);
glm::vec2 step = glm::normalize(dist) * 0.01f;
glm::vec2 step = glm::normalize(glm::vec2(1.f, 1.f));// step in diagonal by default
// special case: perfectly centered (step is null).
if ( glm::length(dist) < EPSILON)
// step in the diagonal
step = glm::vec2(0.01f, 0.01f);
// step in direction of source translation if possible
if ( glm::length(dist) > DELTA_ALPHA)
step = glm::normalize(dist);
// converge linearly to reduce the difference of alpha
float delta = sin_quad(dist.x, dist.y) - CLAMP(a, 0.f, 1.f);
while ( glm::abs(delta) > 0.01f ){
dist += step * glm::sign(delta);
delta = sin_quad(dist.x, dist.y) - CLAMP(a, 0.f, 1.f);
// converge to reduce the difference of alpha
// using dichotomic algorithm
float delta = sin_quad_(dist.x, dist.y) - CLAMP(a, 0.f, 1.f);
while ( glm::abs(delta) > DELTA_ALPHA ){
dist += step * (delta / 2.f);
delta = sin_quad_(dist.x, dist.y) - CLAMP(a, 0.f, 1.f);
}
// apply new mixing coordinates
@@ -512,7 +515,7 @@ void Source::update(float dt)
// read position of the mixing node and interpret this as transparency of render output
glm::vec2 dist = glm::vec2(groups_[View::MIXING]->translation_);
// use the sinusoidal transfer function
blendingshader_->color = glm::vec4(1.f, 1.f, 1.f, sin_quad( dist.x, dist.y ));
blendingshader_->color = glm::vec4(1.f, 1.f, 1.f, sin_quad_( dist.x, dist.y ));
mixingshader_->color = blendingshader_->color;
// CHANGE update status based on limbo