Dart code for drawing a triangle based on starting coordinates, width and inner angles

draw-triangle.dart

void drawLine(x1, y1, x2, y2) {
    ctx.beginPath();
    ctx.moveTo(x1, y1);
    ctx.lineTo(x2, y2);
    ctx.stroke();
  }

  double tanDeg(num x) {
    return tan(x * PI/180);
  }

  void drawTriangle(num x1, num y1, num width, num alpha, num beta) {
    if(!((alpha >= 0 && alpha < 90 && beta == 90) || (alpha == 90 && beta >= 0 && beta < 90)))
      return;
    ctx.beginPath();
    ctx.moveTo(x1, y1);
    ctx.lineTo(x1 + width, y1);


    num angle = alpha < 90 ? alpha : beta;

    num y2 = y1 - tanDeg(angle) * width;
    num x2 = alpha < 90 ? x1 + width : x1;

    ctx.lineTo(x2, y2);
    ctx.lineTo(x1, y1);
    ctx.fill();
  }