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grapher.js
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grapher.js
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/** @type {HTMLCanvasElement} */
function runGrapher() {
const canvas = document.getElementById("graph");
const width = canvas.width;
const height = canvas.height;
const ctx = canvas.getContext("2d");
const FIGURE_COLOR = "#567efb99";
const POINT_COLOR = "#4A76FE99";
const points = [];
function drawGraph() {
ctx.font = "13px sans-serif";
ctx.fillStyle = "#FFF";
ctx.fillRect(0, 0, width, height);
ctx.fillStyle = FIGURE_COLOR;
// 1st quadrant triangle
ctx.beginPath();
ctx.moveTo(width / 2, height / 6);
ctx.lineTo((5 * width) / 6, height / 2);
ctx.lineTo(width / 2, height / 2);
ctx.fill();
ctx.beginPath();
ctx.moveTo(0, height / 2);
ctx.lineTo(width, height / 2);
ctx.lineTo(width - 10, height / 2 - 10);
ctx.moveTo(width, height / 2);
ctx.lineTo(width - 10, height / 2 + 10);
ctx.stroke();
ctx.beginPath();
ctx.moveTo(width / 2, height);
ctx.lineTo(width / 2, 0);
ctx.lineTo(width / 2 - 10, 10);
ctx.moveTo(width / 2, 0);
ctx.lineTo(width / 2 + 10, 10);
ctx.stroke();
// 2nd quadrant sector
ctx.beginPath();
ctx.arc(width / 2, height / 2, width / 3, -1.58, Math.PI, true);
ctx.lineTo(width / 2, height / 2);
ctx.fill();
// 4th quadrant rectangle
ctx.fillRect(width / 2, (3 * height) / 6, width / 6, height / 3);
ctx.fillStyle = "#000";
const labels = ["-R", "-R/2", "", "R/2", "R"];
for (let i = 1; i < 6; i++) {
ctx.beginPath();
ctx.moveTo((i * width) / 6, height / 2 - 5);
ctx.lineTo((i * width) / 6, height / 2 + 5);
ctx.moveTo(width / 2 - 5, (i * height) / 6);
ctx.lineTo(width / 2 + 5, (i * height) / 6);
ctx.stroke();
ctx.textAlign = "center";
ctx.textBaseline = "bottom";
ctx.fillText(labels[i - 1], (i * width) / 6, height / 2 - 7);
ctx.textAlign = "left";
ctx.textBaseline = "middle";
ctx.fillText(labels[i - 1], width / 2 + 7, height - (i * height) / 6);
}
const r = getR();
points.forEach((point, index) => {
const x = ((point.x / r) * width) / 3 + width / 2;
const y = ((-point.y / r) * height) / 3 + height / 2;
ctx.fillStyle = point.color;
ctx.beginPath();
ctx.arc(x, y, 5, 0, Math.PI * 2);
ctx.fill();
});
}
drawGraph();
canvas.onmousemove = (e) => {
drawGraph();
ctx.fillStyle = POINT_COLOR;
ctx.beginPath();
ctx.arc(e.offsetX, e.offsetY, 5, 0, Math.PI * 2);
ctx.fill();
};
canvas.onmouseleave = drawGraph;
//document.getElementById("form").onchange = drawGraph;
canvas.onmousedown = (e) => {
if (!r) {
alert("Please select a value for R first");
return;
}
const xClicked =
Math.round(((2 * e.offsetX) / width - 1) * r * 1.5 * 100) / 100;
const yClicked =
Math.round(((-2 * e.offsetY) / height + 1) * r * 1.5 * 100) / 100;
setX(xClicked);
setY(yClicked);
checkPoint();
};
return {
drawGraph,
};
}