在OpenGL中转换应用顺序令我感到困惑 [英] transform apply order in OpenGL confuse me

问题描述

我阅读了本教程， https://learnopengl.com/Getting-started/Transformations 最后，在最后一张图片的上方，它说:

I read this tutorial, https://learnopengl.com/Getting-started/Transformations At the end, above the last picture, it says:

glm::mat4 trans;
trans = glm::translate(trans, glm::vec3(0.5f, -0.5f, 0.0f));
trans = glm::rotate(trans, (float)glfwGetTime(), glm::vec3(0.0f, 0.0f, 1.0f));

我不知道最终的转换值是什么，它是 translate *旋转或 rotate *翻译吗?

I do not know what is the final trans values is, it is translate * rotate or rotate * translate ?

在这里，我们首先绕原点(0,0,0)旋转容器，然后旋转一次 它旋转了，我们将其旋转版本翻译到右下角 屏幕的一角. 记住实际的转换顺序 应该反读:即使在代码中我们先翻译并 然后旋转，实际的变换首先应用旋转 然后是翻译.

Here we first rotate the container around the origin (0,0,0) and once it's rotated, we translate its rotated version to the bottom-right corner of the screen. Remember that the actual transformation order should be read in reverse: even though in code we first translate and then later rotate, the actual transformations first apply a rotation and then a translation.

那么最后的 transform =翻译*旋转吗? 但是为什么它不写这样的代码:

so the final transform = translate * rotate ? but why it does not write code like this:

glm::mat4 trans;
trans = glm::rotate(trans, (float)glfwGetTime(), glm::vec3(0.0f, 0.0f, 1.0f));
trans = glm::translate(trans, glm::vec3(0.5f, -0.5f, 0.0f)); // revise order

顶点着色器中的代码如下: gl_Position = transform * vec4(aPos, 1.0); 这似乎是 transform =翻译*旋转，因为我们需要先应用旋转"然后进行翻译.

the code in vertex shader is like: gl_Position = transform * vec4(aPos, 1.0); this seems like transform = translate * rotate because we need first apply rotate and then translate.

更新: 因此，我知道乘法需要从右到左读取，因为它是列主矩阵，但是我不明白是在构造转换矩阵时，为什么不使用修订版?

update: So, I know the multiply need read from right to left, because it is column major matrix, but I do not understand is when construct trans matrix, why do not use the revised version ?

推荐答案

输出:

glm::mat4 trans;
trans = glm::translate(trans, glm::vec3(0.5f, -0.5f, 0.0f));
trans = glm::rotate(trans, (float)glfwGetTime(), glm::vec3(0.0f, 0.0f, 1.0f));

应该翻译*旋转，我怀疑作者想模仿从左到右的阅读顺序而不是应用顺序.您可以通过查看源代码:

Should be translate*rotate, I suspect that the authors wanted to mimic the left-to-right reading order not the order in which they are applied. You can confirm this by looking throught source code:

template<typename T, qualifier Q>
GLM_FUNC_QUALIFIER mat<4, 4, T, Q> translate(mat<4, 4, T, Q> const& m, vec<3, T, Q> const& v)
{
    mat<4, 4, T, Q> Result(m);
    Result[3] = m[0] * v[0] + m[1] * v[1] + m[2] * v[2] + m[3];
    return Result;
}

这将计算 m * translationMat .因为翻译矩阵的顶部3x3角是单位，而第四列是(v,1.0).

This computes m*translationMat. Because the top 3x3 corner for the translation matrix is the identity and fourth column is (v,1.0).

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