ConeGeometry contains degenerate triangles

[gkjohnson]

Description

ConeGeometry extends CylinderGeometry and simply sets the top radius to 0 resulting in one triangle of all the 2-triangle rectanglar sides being reduced to an edge. Eg a cone with 3 sides should require a total of 6 triangles - but instead consists of 9. 3 of which are degenerate triangles.

You can see the triangles that are being reduced to an edge as the top radius gets smaller:

Degenerate triangles like this can cause issues with any algorithms that require computing triangle normals, take surface area, generating half-edge structures, etc. It would be great if the core three.js primitives could be properly constructed without degenerate triangle issues.

Reproduction steps

1. Create a cone geometry
2. Check the number of triangles
3. There are are more triangles than necessary

Code

const cone = new THREE.ConeGeometry( 1, 1, 3, 1 );
console.log( cone.index.count / 3 ); // logs 9 instead of 6

Live example

• jsfiddle-latest-release WebGLRenderer
• jsfiddle-dev WebGLRenderer
• jsfiddle-latest-release WebGPURenderer
• jsfiddle-dev WebGPURenderer

Screenshots

No response

Version

dev

Device

No response

Browser

No response

OS

No response

[andrewhodel]

It's probably using a double instead of an integer with a known range.

You'll need to do this instead of N.DDDDD / N * .DDDDD:

		var currentStep = 0;
		for (var c=0; c<totalSteps; c++) {
			if (desiredRation >= ration_step*c)) {
				currentStep = c;
			}
		}