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Question

为什么resultA不等于resultB？我不知道我做错了什么。你能给我一个解释吗？

float alpha = glm::radians(45.0f);

glm::mat4 xRot(glm::vec4(1, 0, 0, 0),
               glm::vec4(0, glm::cos(alpha), glm::sin(alpha), 0),
               glm::vec4(0, -glm::sin(alpha), glm::cos(alpha), 0),
               glm::vec4(0, 0, 0, 1));

glm::mat4 yRot(glm::vec4(glm::cos(alpha), 0, -glm::sin(alpha), 0),
               glm::vec4(0, 1, 0, 0),
               glm::vec4(glm::sin(alpha), 0, glm::cos(alpha), 0),
               glm::vec4(0, 0, 0, 1));

glm::vec4 vec(0, 0, -100, 1);

glm::vec4 resultA(0.0f);
glm::vec4 resultB(0.0f);

resultA = xRot  * yRot * vec; //(-70.7107, 50, -50, 1)
resultB = yRot  * xRot * vec; //(-50, 70.7107, -50, 1)

Answer 1

一般情况下，3D旋转不会往返，除非在非常特殊的情况下。因此：

xRot * yRot != yRot * xRot

从本质上讲，您正在使用上面的内容来证明这一点:)

查看此处：http://en.wikipedia.org/wiki/Commutative_property