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Code Issues Releases Wiki Activity

tweaks to arc approx, offsetting, and tangents

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Pomax
2016-01-09 23:01:08 -08:00
parent 9ede7b4143
commit 66e17b515c
4 changed files with 135 additions and 28 deletions
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37
components/sections/arcapproximation/index.js
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@@ -24,6 +24,23 @@ var Introduction = React.createClass({
setupCubic: function(api) {
var curve = api.getDefaultCubic();
api.setCurve(curve);
api.error = 0.5;
},
values: {
"38": 0.1, // up arrow
"40": -0.1, // down arrow
},
onKeyDown: function(e, api) {
var v = this.values[e.keyCode];
if(v) {
e.preventDefault();
api.error += v;
if (api.error < 0.1) {
api.error = 0.1;
}
}
},
getCCenter: function(api, p1, p2, p3) {
@@ -111,7 +128,7 @@ var Introduction = React.createClass({
drawSingleArc: function(api, curve) {
api.reset();
var arcs = curve.arcs(0.5);
var arcs = curve.arcs(api.error);
api.drawSkeleton(curve);
api.drawCurve(curve);
@@ -120,11 +137,14 @@ var Introduction = React.createClass({
api.setFill("rgba(200,0,0,0.4)");
api.debug = true;
api.drawArc(a);
api.setFill("black");
api.text("Arc approximation with total error " + api.utils.round(api.error,1), {x:10, y:15});
},
drawArcs: function(api, curve) {
api.reset();
var arcs = curve.arcs(0.5);
var arcs = curve.arcs(api.error);
api.drawSkeleton(curve);
api.drawCurve(curve);
arcs.forEach(a => {
@@ -132,6 +152,9 @@ var Introduction = React.createClass({
api.setFill(api.getColor());
api.drawArc(a);
});
api.setFill("black");
api.text("Arc approximation with total error " + api.utils.round(api.error,1) + " per arc segment", {x:10, y:15});
},
render: function() {
@@ -210,11 +233,11 @@ var Introduction = React.createClass({
<p>The following graphic shows the result of this approach, with a default error threshold of 0.5, meaning that
if an arc is off by a <em>combined</em> half pixel over both verification points, then we treat the arc as bad.
This is an extremely simple error policy, but already works really well. Note that the graphic is still interactive,
and you can use your '+' and '-' keys to increase to decrease the error threshold, to see what the effect
of a smaller or larger error threshold is.</p>
This is an extremely simple error policy, but already works really well. Note that the graphic is still
interactive, and you can use your up and down cursor keys keys to increase or decrease the error threshold,
to see what the effect of a smaller or larger error threshold is.</p>
<Graphic preset="simple" title="Arc approximation of a Bézier curve" setup={this.setupCubic} draw={this.drawSingleArc} />
<Graphic preset="simple" title="Arc approximation of a Bézier curve" setup={this.setupCubic} draw={this.drawSingleArc} onKeyDown={this.onKeyDown} />
<p>With that in place, all that's left now is to "restart" the procedure by treating the found arc's
end point as the new to-be-determined arc's starting point, and using points further down the curve. We
@@ -223,7 +246,7 @@ var Introduction = React.createClass({
so you can see how picking a different threshold changes the number of arcs that are necessary to
reasonably approximate a curve:</p>
<Graphic preset="simple" title="Arc approximation of a Bézier curve" setup={this.setupCubic} draw={this.drawArcs} />
<Graphic preset="simple" title="Arc approximation of a Bézier curve" setup={this.setupCubic} draw={this.drawArcs} onKeyDown={this.onKeyDown} />
<p>So... what is this good for? Obviously, If you're working with technologies that can't do curves,
but can do lines and circles, then the answer is pretty straight-forward, but what else? There are

35
components/sections/offsetting/index.js
View File

@@ -27,15 +27,33 @@ var Offsetting = React.createClass({
draw: function(api, curve) {
api.reset();
api.drawSkeleton(curve);
api.drawCurve(curve);
var reduced = curve.reduce();
reduced.forEach(c => {
api.setRandomColor();
api.drawCurve(c);
api.drawCircle(c.points[0], 3);
});
var last = reduced.slice(-1)[0];
api.drawCircle(last.points[3] || last.points[2],3);
api.setColor("red");
var offset = curve.offset(api.distance);
offset.forEach(c => api.drawCurve(c));
offset.forEach(c => {
api.drawCircle(c.points[0],1);
api.drawCurve(c)
});
last = offset.slice(-1)[0];
api.drawCircle(last.points[3] || last.points[2],1);
api.setColor("blue");
offset = curve.offset(-api.distance);
offset.forEach(c => api.drawCurve(c));
offset.forEach(c => {
api.drawCircle(c.points[0],1);
api.drawCurve(c)
});
last = offset.slice(-1)[0];
api.drawCircle(last.points[3] || last.points[2],1);
},
values: {
@@ -153,8 +171,17 @@ var Offsetting = React.createClass({
with respect to the curve's scaling origin (which is the intersection of the point normals at the start
and end points).</p>
<p>A good way to do this reduction is to first find the curve's extreme points, as explained in the earlier
section on curve extremities, and use these as initial splitting points. After this initial split, we can
check each individual segment to see if it's "safe enough" based on where the center of the curve is. If the
on-curve point for <i>t=0.5</i> is too far off from the center, we simply split the segment down the middle.
Generally this is more than enough to end up with safe segments.</p>
<p>The following graphics show off curve offsetting, and you can use your up and down cursor keys to control
the distance at which the curve gets offset:</p>
the distance at which the curve gets offset. The curve first gets reduced to safe segments, each of which is
then offset at the desired distance. Especially for simple curves, particularly easily set up for quadratic
curves, no reduction is necessary, but the more twisty the curve gets, the more the curve needs to be reduced
in order to get segments that can safely be scaled.</p>
<Graphic preset="simple" title="Offsetting a quadratic Bézier curve" setup={this.setupQuadratic} draw={this.draw} onKeyDown={this.onKeyDown} />
<Graphic preset="simple" title="Offsetting a cubic Bézier curve" setup={this.setupCubic} draw={this.draw} onKeyDown={this.onKeyDown} />

10
components/sections/pointvectors/index.js
View File

@@ -22,16 +22,17 @@ var PointVectors = React.createClass({
draw: function(api, curve) {
api.reset();
api.drawSkeleton(curve);
api.drawCurve(curve);
var i,t,p,tg,n,td=0.25,nd=20;
var i,t,p,tg,n,m,nd=20;
for(i=0; i<=10; i++) {
t = i/10.0;
p = curve.get(t);
tg = curve.derivative(t);
m = Math.sqrt(tg.x*tg.x + tg.y*tg.y);
tg = {x:tg.x/m, y:tg.y/m};
n = curve.normal(t);
api.setColor("blue");
api.drawLine(p, {x:p.x+tg.x*td, y:p.y+tg.y*td});
api.drawLine(p, {x:p.x+tg.x*nd, y:p.y+tg.y*nd});
api.setColor("red");
api.drawLine(p, {x:p.x+n.x*nd, y:p.y+n.y*nd});
api.setColor("black");
@@ -132,7 +133,8 @@ var PointVectors = React.createClass({
</div>
<p>The following two graphics show the tangent and normal along a quadratic and cubic curve, with
the direction vector coloured blue, and the normal vector coloured red.</p>
the direction vector coloured blue, and the normal vector coloured red (the markers are spaced out
evenly as <i>t</i>-intervals, not spaced equidistant).</p>
<div className="figure">
<Graphic preset="simple" title="Quadratic Bézier tangents and normals" inline={true} setup={this.setupQuadratic} draw={this.draw}/>