getStrokeOutlinePoints function
Get an array of points representing the outline of a stroke, based on the provided points. Used internally by getStroke but possibly of separate interest. Accepts the result of getStrokeOutlinePoints.
The size argument sets the base diameter for the shape.
The thinning argument sets the effect of pressure on the stroke's size.
The smoothing argument sets the density of points along the stroke's edges.
The streamline argument sets the level of variation allowed in the input points.
The taperStart argument sets the distance to taper the front of the stroke.
The capStart argument sets whether to add a cap to the start of the stroke.
The taperEnd argument sets the distance to taper the end of the stroke.
The capEnd argument sets whether to add a cap to the end of the stroke.
The simulatePressure argument sets whether to simulate pressure or use the point's provided pressures.
The isComplete argument sets whether the line is complete.
Implementation
List<Point> getStrokeOutlinePoints(
List<StrokePoint> points, {
double size = 16,
double thinning = 0.7,
double smoothing = 0.5,
double streamline = 0.5,
double taperStart = 0.0,
double taperEnd = 0.0,
bool capStart = true,
bool capEnd = true,
bool simulatePressure = true,
bool isComplete = false,
}) {
if (points.isEmpty || size < 0) return [];
final totalLength = points.last.runningLength;
final minDistance = pow(size * smoothing, 2);
final leftPts = <Point>[];
final rightPts = <Point>[];
double prevPressure = points[0].point.p;
double sp;
double rp;
for (var i = 0; i < min(10, points.length); i++) {
var pressure = points[i].point.p;
if (simulatePressure) {
sp = min(1, points[i].distance / size);
rp = min(1, 1 - sp);
pressure = min(
1,
prevPressure + (rp - prevPressure) * (sp * rateOfPressureChange),
);
}
prevPressure = (prevPressure + pressure) / 2;
}
double radius = getStrokeRadius(
size,
thinning,
points.last.point.p,
);
double? firstRadius;
var prevVector = points[0].vector;
var pl = points[0].point;
var pr = pl;
var tl = pl;
var tr = pr;
Point nextVector;
Point offset;
double nextDpr;
double ts;
double te;
for (var i = 0; i < points.length - 1; i++) {
final curr = points[i];
if (totalLength - curr.runningLength < 3) continue;
// Pressure
var pressure = curr.point.p;
if (thinning != 0) {
if (simulatePressure) {
sp = min(1, curr.distance / size);
rp = min(1, 1 - sp);
pressure = min(
1,
prevPressure + (rp - prevPressure) * (sp * rateOfPressureChange),
);
radius = getStrokeRadius(
size,
thinning,
pressure,
);
} else {
radius = size / 2;
}
}
firstRadius ??= radius;
// Tapering
if (curr.runningLength < taperStart) {
ts = curr.runningLength / taperStart;
} else {
ts = 1;
}
if (totalLength - curr.runningLength < taperEnd) {
te = (totalLength - curr.runningLength) / taperEnd;
} else {
te = 1;
}
radius = max(0.01, radius * min(ts, te));
// Left and Right Points
nextVector = points[i + 1].vector;
nextDpr = dpr(curr.vector, nextVector);
if (nextDpr < 0) {
// Sharp Corner
final offset = mul(per(prevVector), radius);
const step = 1 / 13;
for (double t = 0; t <= 1; t += step) {
tl = rotAround(sub(curr.point, offset), curr.point, pi * t);
leftPts.add(tl);
tr = rotAround(add(curr.point, offset), curr.point, pi * -t);
rightPts.add(tr);
}
pl = tl;
pr = tr;
continue;
}
// Regular points
offset = mul(per(lrp(nextVector, curr.vector, nextDpr)), radius);
tl = sub(curr.point, offset);
if (i == 0 || dist2(pl, tl) > minDistance) {
leftPts.add(tl);
pl = tl;
}
tr = add(curr.point, offset);
if (i == 0 || dist2(pr, tr) > minDistance) {
rightPts.add(tr);
pr = tr;
}
prevPressure = pressure;
prevVector = curr.vector;
}
final firstPoint = points.first.point;
final lastPoint = () {
if (points.length > 1) {
return points.last.point;
} else {
return add(
firstPoint,
Point(1, 1),
);
}
}();
final isVeryShort = leftPts.length <= 1 || rightPts.length <= 1;
final startCap = <Point>[];
final endCap = <Point>[];
if (isVeryShort) {
if (!(taperStart > 0 || taperEnd > 0) || isComplete) {
final start = prj(
firstPoint,
uni(per(sub(firstPoint, lastPoint))),
-(firstRadius ??= radius),
);
final dotPts = <Point>[];
const step = 1 / 13;
for (double t = step; t <= 1; t += step) {
dotPts.add(rotAround(start, firstPoint, pi * 2 * t));
}
return dotPts;
}
} else {
// Start Cap
if (taperStart > 0 || (taperEnd > 0 && isVeryShort)) {
// noop
} else if (capStart) {
const step = 1 / 13;
for (double t = step; t <= 1; t += step) {
startCap.add(rotAround(rightPts.first, firstPoint, pi * t));
}
} else {
final cornersVector = sub(leftPts.first, rightPts.first);
final offsetA = mul(cornersVector, 0.5);
final offsetB = mul(cornersVector, 0.51);
startCap.addAll(
[
sub(firstPoint, offsetA),
sub(firstPoint, offsetB),
add(firstPoint, offsetB),
add(firstPoint, offsetA),
],
);
}
// End Cap
final mid = med(leftPts.last, rightPts.last);
final direction = per(uni(sub(lastPoint, mid)));
if (taperEnd > 0 || (taperStart > 0 && isVeryShort)) {
endCap.add(lastPoint);
} else if (capEnd) {
final start = prj(lastPoint, direction, radius);
const step = 1 / 29;
for (double t = 0; t <= 1; t += step) {
endCap.add(rotAround(start, lastPoint, pi * 3 * t));
}
} else {
endCap.addAll([
sub(lastPoint, mul(direction, radius)),
sub(lastPoint, mul(direction, radius * .99)),
add(lastPoint, mul(direction, radius * .99)),
add(lastPoint, mul(direction, radius))
]);
}
}
return [
...leftPts,
...endCap,
...rightPts.reversed,
...startCap,
];
}