SLANTMAKER.js

const fs = require("fs");

const inquirer = require("inquirer");

async function main() {
  console.log("Ready");
  const answers = await inquirer.prompt([
    {
      type: "input",
      filter: parseFloat,
      name: "width",
      message: "How wide are the stripes?"
    },
    {
      type: "input",
      filter: parseFloat,
      name: "height",
      message: "How long are the stripes?"
    },
    {
      type: "input",
      filter: parseFloat,
      name: "variance",
      message: "Maximum opacity variance column to column (as percent decimal)?"
    },
    {
      type: "input",
      filter: parseFloat,
      name: "verticalVariance",
      message: "Maximum opacity variance stripe to stripe (as percent decimal)?"
    },
    {
      type: "input",
      filter: parseFloat,
      name: "initial",
      message: "What's the initial opacity (as percent decimal)?"
    },
    {
      type: "input",
      filter: parseFloat,
      name: "stripesPerColumn",
      message: "How many stripes are in a column?"
    },
    {
      type: "input",
      filter: parseFloat,
      name: "columnCount",
      message: "How many columns?"
    }
  ]);

  const halfWidth = answers.width / 2;
  const halfHeight = answers.height / 2;

  const output = fs.createWriteStream("slants.svg");

  const startOffset = -1 * halfWidth * answers.stripesPerColumn;
  const totalHeight = answers.stripesPerColumn * halfHeight;
  const totalWidth = startOffset + answers.width * answers.columnCount;

  output.write(
    `<svg height="${totalHeight}" width="${totalWidth}" xmlns="http://www.w3.org/2000/svg">`
  );
  output.write('<g stroke="none" fill="red">');
  function drawStripe(xOffset, yOffset, opacity) {
    if (xOffset + answers.width < 0 || xOffset >= totalWidth) {
      return;
    }
    output.write(
      `<path d="M${xOffset} ${totalHeight - yOffset}l${halfWidth} ${-1 *
        halfHeight}l${halfWidth} ${halfHeight}l${-1 *
        halfWidth} ${halfHeight}" opacity="${opacity}" />`
    );
  }

  function drawColumn(xOffset) {
    const initialOpacity =
      answers.initial + (Math.random() - 0.5 * 2) * answers.variance;
    const opacityStep = initialOpacity / answers.stripesPerColumn;
    for (let i = 0; i < answers.stripesPerColumn; i++) {
      const baseOpacity = initialOpacity - opacityStep * i;
      const stripeOpacity =
        (Math.random() - 0.5) * 2 * answers.verticalVariance;
      drawStripe(
        xOffset + i * halfWidth,
        i * halfHeight,
        baseOpacity + stripeOpacity
      );
    }
  }

  let start = startOffset;
  for (let i = 0; i < answers.columnCount; i++) {
    drawColumn(start);
    start += answers.width;
  }

  output.write("</g>");
  output.end("</svg>");
}

main();