我有一个缩放 (20, 20, 1) 和旋转 90 度的变换矩阵：
0, -20, 0, 80
20, 0, 0, 20
0, 0, 1, 0
0, 0, 0, 1
我想要缩放。我在 JavaScript 中有下一个示例，其中包含 glMatrix 库，该库从上面的转换矩阵中提取缩放比例：
<body>
<!-- Since import maps are not yet supported by all browsers, its is
necessary to add the polyfill es-module-shims.js -->
<script async src="https://unpkg.com/[email protected]/dist/es-module-shims.js">
</script>
<script type="importmap">
{
"imports": {
"gl-matrix": "https://cdn.jsdelivr.net/npm/[email protected]/+esm"
}
}
</script>
<script type="module">
import { mat4, vec3 } from "gl-matrix";
// Create a matrix
const matrix = mat4.fromValues(
0, 20, 0, 0,
-20, 0, 0, 0,
0, 0, 1, 0,
80, 20, 0, 1);
// Extract scaling
const scaling = vec3.create();
mat4.getScaling(scaling, matrix);
console.log(scaling[0], scaling[1], scaling[2]);
</script>
</body>
我想将其重写为Qt。我阅读了文档并尝试谷歌，但我没有找到如何从转换矩阵中提取缩放比例。
#include <QtGui/QMatrix4x4>
#include <QtWidgets/QApplication>
#include <QtWidgets/QWidget>
class Widget : public QWidget
{
public:
Widget()
{
QMatrix4x4 matrix(
0, -20, 0, 80,
20, 0, 0, 20,
0, 0, 1, 0,
0, 0, 0, 1);
qDebug() << "hello";
}
};
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
Widget w;
w.show();
return app.exec();
}
我打开了
getScalingexport function getScaling(out, mat) {
let m11 = mat[0];
let m12 = mat[1];
let m13 = mat[2];
let m21 = mat[4];
let m22 = mat[5];
let m23 = mat[6];
let m31 = mat[8];
let m32 = mat[9];
let m33 = mat[10];
out[0] = Math.hypot(m11, m12, m13);
out[1] = Math.hypot(m21, m22, m23);
out[2] = Math.hypot(m31, m32, m33);
return out;
}
我用qHypot
做了同样的事情#include <QtGui/QMatrix4x4>
#include <QtGui/QVector3D>
#include <QtMath>
#include <QtWidgets/QApplication>
#include <QtWidgets/QWidget>
class Widget : public QWidget
{
public:
Widget()
{
QMatrix4x4 m(
0, -20, 0, 80,
20, 0, 0, 20,
0, 0, 1, 0,
0, 0, 0, 1);
float sx = qHypot(m.row(0)[0], m.row(1)[0], m.row(2)[0]);
float sy = qHypot(m.row(0)[1], m.row(1)[1], m.row(2)[1]);
float sz = qHypot(m.row(0)[2], m.row(1)[2], m.row(2)[2]);
QVector3D scaling(sx, sy, sz);
qDebug() << scaling;
}
};
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
Widget w;
w.show();
return app.exec();
}
附注QMatrix4x4 构造函数 使用行优先顺序。 glMatrix fromValues 方法使用列优先顺序。