如何在三边JS上绘制三角形？

Question

I will have 3 inputs and a button. When you click on this button you should draw a triangle in which the lengths of 3 sides are equal to the values in the inputs. How to organize it? I found this:

context.beginPath();
context.moveTo(30, 20);
context.lineTo(some_value1,some_value2);
context.lineTo(some_value3,some_value4);
context.closePath();

But this method is suitable for drawing, on two sides. I hope now I have described the problem in detail. Thanks in advance.

Answer 1

You will need to compute cartesian coordinates of each point first. You can set the first point to [0, 0] , and the second will be at [x1, 0] where x1 is length of first line. Third point needs to be calculated, take a look here how this can be done:

https://math.stackexchange.com/questions/543961/determine-third-point-of-triangle-when-two-points-and-all-sides-are-known

 // hardcoded, but you would get those from user var AB = 40; var BC = 50; var AC = 30; var A = [0, 0]; // starting coordinates var B = [0, AB]; var C = []; // calculate third point C[1] = (AB * AB + AC * AC - BC * BC) / (2 * AB); C[0] = Math.sqrt(AC * AC - C[1] * C[1]); console.log(A, B, C); var canvas = document.getElementById('canvas'); var ctx = canvas.getContext('2d'); ctx.beginPath(); ctx.moveTo(A[0], A[1]); ctx.lineTo(B[0], B[1]); ctx.lineTo(C[0], C[1]); ctx.fill(); 

 <canvas id="canvas" width="500" height="500"></canvas>