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# Example:
# When $this has region /r/ {
# lassign [region centroid $r] x y
# Wish to draw an arc with x $x y $y start 0 arclen 1 thickness 3 radius 100 color green
# }
Wish the GPU compiles pipeline "arc" {{vec2 center float start float arclen float radius float thickness vec4 color} {
float r = radius + thickness;
vec2 vertices[4] = vec2[4](
center - r,
vec2(center.x + r, center.y - r),
vec2(center.x - r, center.y + r),
center + r
);
return vertices[gl_VertexIndex];
} {
#define M_TWO_PI 6.283185307179586
start = clamp(start, 0, M_TWO_PI);
arclen = clamp(arclen, 0, M_TWO_PI);
float dist = length(gl_FragCoord.xy - center) - radius;
float angle = atan(-(gl_FragCoord.y - center.y), gl_FragCoord.x - center.x);
// Shift angle from [-pi, pi) to [0, 2*pi]
angle = (angle < 0) ? (angle + M_TWO_PI) : angle;
float end = start + arclen;
return ((dist < thickness && dist > 0.0) &&
((end < M_TWO_PI && angle > start && angle < end) ||
(end >= M_TWO_PI && (angle > start || angle < end-M_TWO_PI)))) ? color : vec4(0, 0, 0, 0);
}}
When /someone/ wishes to draw an arc with /...options/ {
dict with options {
Wish the GPU draws pipeline "arc" with arguments \
[list [list $x $y] $start $arclen $radius $thickness [getColor $color]]
}
}
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