Use Geometric.js to determine whether a point is to the left or right of a line.
To The Left, To The Right
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| license: gpl-3.0 |
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| <!DOCTYPE html> | |
| <html> | |
| <head> | |
| <style> | |
| body { | |
| margin: 0; | |
| } | |
| line { | |
| stroke: #000; | |
| } | |
| polygon { | |
| fill: none; | |
| } | |
| .left.active { | |
| fill: steelblue; | |
| } | |
| .right.active { | |
| fill: tomato; | |
| } | |
| </style> | |
| </head> | |
| <body> | |
| <script src="https://d3js.org/d3-selection.v1.min.js"></script> | |
| <script src="https://unpkg.com/jeezy@1.13.0/lib/jeezy.min.js"></script> | |
| <script src="https://unpkg.com/geometric@1.0.0/build/geometric.min.js"></script> | |
| <script> | |
| var width = window.innerWidth, height = window.innerHeight, halfWidth = width / 2; | |
| var pointA = [jz.num.randBetween(halfWidth + 200, halfWidth), 0]; | |
| var pointB = [jz.num.randBetween(halfWidth, halfWidth - 200), height]; | |
| var svg = d3.select("body").append("svg") | |
| .attr("width", width) | |
| .attr("height", height) | |
| var line = svg.append("line") | |
| .attr("x1", pointA[0]) | |
| .attr("y1", pointA[1]) | |
| .attr("x2", pointB[0]) | |
| .attr("y2", pointB[1]); | |
| var left = svg.append("polygon") | |
| .attr("class", "left") | |
| .attr("points", [[0, 0], [pointA], [pointB], [0, height]].join(" ")); | |
| var right = svg.append("polygon") | |
| .attr("class", "right") | |
| .attr("points", [[width, 0], [pointA], [pointB], [width, height]].join(" ")); | |
| svg.on("mousemove", _ => { | |
| var p = [d3.event.pageX, d3.event.pageY]; | |
| var leftOfLine = geometric.pointLeftofLine(p, [pointA, pointB]); | |
| var rightOfLine = geometric.pointRightofLine(p, [pointA, pointB]); | |
| left.classed("active", leftOfLine); | |
| right.classed("active", rightOfLine); | |
| }); | |
| </script> | |
| </body> | |
| </html> |
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