html - How to draw a 3D sphere?

Question

I want to draw a 3D ball or sphere in HTML 5.0 canvas. I want to understand the Algorithm about how to draw a 3D sphere. Who can share this with me?

Answer 1

You will need to model a sphere, and have it be varying colors so that as it rotates you can see that it is not only a sphere, but being rendered.

Otherwise, a sphere in space, with not point of reference around it looks like a circle, if it is all one solid color.

To start with you will want to try drawing a circle with rectangles, as that is the main primitive you have.

Once you understand how to do that, or create a new primitive, such as a triangle, using the Path method, and create a circle, then you are ready to move it to 3D.

3D is just a trick, as you will take your model, probably generated by an equation, and then flatten it, as you determine which parts will be seen, and then display it.

But, you will want to change the color of the triangles based on how far they are from a source of light, as well as based on the angle of that part to the light source.

This is where you can start to do optimizations, as, if you do this pixel by pixel then you are raytracing. If you have larger blocks, and a point source of light, and the object is rotating but not moving around then you can recalculate how the color changes for each triangle, then it is just a matter of changing colors to simulate rotating.

The algorithm will depend on what simplifications you want to make, so as you gain experience come back and ask, showing what you have done so far.

Here is an example of doing it, and below I copied the 3D sphere part, but please look at the entire article.

function Sphere3D(radius) {
 this.point = new Array();
 this.color = "rgb(100,0,255)"
 this.radius = (typeof(radius) == "undefined") ? 20.0 : radius;
 this.radius = (typeof(radius) != "number") ? 20.0 : radius;
 this.numberOfVertexes = 0;

 // Loop from 0 to 360 degrees with a pitch of 10 degrees ... 
  for(alpha = 0; alpha <= 6.28; alpha += 0.17) {
   p = this.point[this.numberOfVertexes] = new Point3D();

   p.x = Math.cos(alpha) * this.radius;
   p.y = 0;
   p.z = Math.sin(alpha) * this.radius;

   this.numberOfVertexes++;
 }

 // Loop from 0 to 90 degrees with a pitch of 10 degrees ... 
 // (direction = 1)

 // Loop from 0 to 90 degrees with a pitch of 10 degrees ...
 // (direction = -1)

 for(var direction = 1; direction >= -1; direction -= 2) {
   for(var beta = 0.17; beta < 1.445; beta += 0.17) {

     var radius = Math.cos(beta) * this.radius;
     var fixedY = Math.sin(beta) * this.radius * direction;

     for(var alpha = 0; alpha < 6.28; alpha += 0.17) {
       p = this.point[this.numberOfVertexes] = new Point3D();

       p.x = Math.cos(alpha) * radius;
       p.y = fixedY;
       p.z = Math.sin(alpha) * radius;

       this.numberOfVertexes++;
     }
   }
 }
}