@jscad/modeling
Version:
Constructive Solid Geometry (CSG) Library for JSCAD
30 lines (26 loc) • 888 B
JavaScript
const fromValues = require('../vec2/fromValues')
/**
* Multiply a 2D vector by a matrix (interpreted as 2 row, 1 column).
*
* Calculation: result = v*M, where the fourth element is set to 1.
* @param {vec2} vector - input vector
* @param {mat4} matrix - input matrix
* @returns {vec2} a new vector
* @alias module:modeling/maths/mat4.rightMultiplyVec2
*/
const rightMultiplyVec2 = (vector, matrix) => {
const [v0, v1] = vector
const v2 = 0
const v3 = 1
let x = v0 * matrix[0] + v1 * matrix[1] + v2 * matrix[2] + v3 * matrix[3]
let y = v0 * matrix[4] + v1 * matrix[5] + v2 * matrix[6] + v3 * matrix[7]
const w = v0 * matrix[12] + v1 * matrix[13] + v2 * matrix[14] + v3 * matrix[15]
// scale such that fourth element becomes 1:
if (w !== 1) {
const invw = 1.0 / w
x *= invw
y *= invw
}
return fromValues(x, y)
}
module.exports = rightMultiplyVec2