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layout(triangles) in;
layout(triangle_strip, max_vertices=3) out;
uniform float outlineWidth = 1.0;
uniform vec2 viewportSize;
in vec4 pos_xformed[];
in float widthModulator[];
noperspective out vec3 distanceToOutline;
// project to screen space
vec2 proj(int axis) {
vec4 pos = pos_xformed[axis];
return (0.5 * (pos.xy / pos.w) + 0.5) * viewportSize;
}
float dist(vec2 pos[3], int v) {
// current vertex position
vec2 vpos = pos[v];
// endpoints of opposite edge
vec2 e1 = pos[(v + 1) % 3];
vec2 e2 = pos[(v + 2) % 3];
float abs_det = length(cross(vec3(vpos - e1, 0), vec3(vpos - e2, 0))); // could simplify
return abs_det / distance(e2, e1);
}
vec3 distance[3];
void clearEdge(int v) {
float distant = 10 * outlineWidth;
for (int i = 0; i < 3; ++i)
distance[i][v] += distant;
}
void modulateEdge(int v) {
float offset = min(widthModulator[v],1) * outlineWidth;
for (int i = 0; i < 3; ++i)
distance[i][v] -= offset;
}
void main() {
vec2 pos[3] = vec2[3](proj(0), proj(1), proj(2));
for (int v = 0; v < 3; ++v)
distance[v] = vec3(0);
for (int v = 0; v < 3; ++v) {
if (widthModulator[v] > 0) {
distance[v][v] = dist(pos, v);
modulateEdge(v);
}
}
for (int v = 0; v < 3; ++v)
if (widthModulator[v] <= 0)
clearEdge(v);
for (int v = 0; v < 3; ++v) {
gl_Position = pos_xformed[v];
distanceToOutline = distance[v];
EmitVertex();
}
EndPrimitive();
}
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