WebGL显示不带矩阵的加载模型

Question

I'm learning webgl. I've managed to draw stuff and hopefully understood the pipeline. Now, every tutorial I see explains matrices before even loading a mesh. While it can be good for most, I think I need to concentrate on the process of loading external geometry, maybe through a json file. I've read that openGL by default displays things orthogonally, so I ask: is it possible to display a 3d mesh without any kind of transformation?

Answer 1

Now, every tutorial I see explains matrices before even loading a mesh.

Yes. Because understanding transformations is essential and you will need to work with them. They're not hard to understand and the sooner you wrap your head around them, the better. Actually in the case of OpenGL for the model-view transformation part it's actually rather simple:

The transformation matrix is just a bunch of vectors (in columns) placed within a "parent" coordinate system. The first the columns define how the X, Y and Z axes of the "embedded" coordinate system are aligned within the "parent", the W column moves it around. By varying the lengths of the base vectors you can stretc, ie scale things.

That's it, there's nothing more to it (in the modelview) than that. Learn the rules of matrix-matrix multiplication. Matrix-vector multiplication is just a special case of matrix-matrix multiplication.

The projection matrix is a little bit trickier, but I suggest you don't bother too much with it, just use GLM, Eigen::3D or linmath.h to build the matrix. The best analogy for the projection matrix is being the "lens" of OpenGL, ie this is where you apply zoom (aka field of view), tilt and shift. But the place of the "camera" is defined through the modelview.

is it possible to display a 3d mesh without any kind of transformation?

No. Because the mesh coordinates have to be transformed into screen coordinates. However a identity transform is perfectly possible, which, yes, looks like a dead on orthographic projection where the coordinate range [-1, 1] in either dimension is mapped to fill the viewport.