opengl斜投影 [英] opengl oblique projection
问题描述
我想在OpenGL中创建一个倾斜(cavalier)投影。我知道这个操作不是默认支持,而是我需要一个剪切矩阵,然后进行正交投影。
你能告诉我什么是OpenGl步骤/功能,我
我以前没有使用倾斜/骑士投影,但下面应该给你一个想法如何处理:
创建4x4剪切矩阵,
H (θ,Φ)= | 1,0,-cot(θ),0 |
| 0,1,-cot(Φ),0 |
| 0,0,1,0 |
| 0,0,0,1 |
θ是X中的剪切,Φ是Y中的剪切, / p>
乘以正交投影乘以
| 2 /(r-1),0,0, - (r + 1)/(r-1)|
| 0,2 /(t-b),0, - (t + b)/(t-b)|
| 0,0 / 2 /(f-n), - (f + n)/(f-n)|
| 0,0,0,1 |
(由left,right,bottom,top,near和far描述)
b$ b
(ref: http://en.wikipedia.org/wiki/Orthographic_projection_ %28geometry%29 )
然后,OpenGL允许你通过函数 glLoadMatrixf():
GLfloat proj [16] = {...};
glMatrixMode(GL_PROJECTION); //确保我们修改* projection * matrix
glLoadMatrixf(proj); //加载投影
要深入了解OpenGL中的查看和转换如何工作,请参阅 OpenGL红皮书第3章。他们使用 glOrtho()创建和应用正投影。
编辑:
正如datenwolf指出的,记住OpenGL中的矩阵元素是以列为主的顺序指定的。 / p>
I want to create a oblique (cavalier) projection in OpenGL. I know this operation is not default supported and instead I need a Shear Matrix and then make an Orthogonal Projection.
Can you tell me what are the OpenGl steps / functions that I have to make?
I've not used a oblique/cavalier projection before, but the following should give you an idea of how to proceed:
Create a 4x4 shear matrix,
H(θ, Φ) = | 1, 0, -cot(θ), 0 |
| 0, 1, -cot(Φ), 0 |
| 0, 0, 1, 0 |
| 0, 0, 0, 1 |
θ being the shear in X, Φ being the shear in Y, and Z being left alone.
(ref: slide 11 of http://www.cs.unm.edu/~angel/CS433/LECTURES/CS433_17.pdf)
Multiply that by your orthographic projection,
| 2/(r-l), 0, 0, -(r+l)/(r-l) |
| 0, 2/(t-b), 0, -(t+b)/(t-b) |
| 0, 0, 2/(f-n), -(f+n)/(f-n) |
| 0, 0, 0, 1 |
(described by, left, right, bottom, top, near and far)
(ref: http://en.wikipedia.org/wiki/Orthographic_projection_%28geometry%29)
OpenGL then allows you to upload this matrix directly (as an array of 16 floats) via the function glLoadMatrixf():
GLfloat proj[16] = { ... };
glMatrixMode(GL_PROJECTION); // Make sure we're modifying the *projection* matrix
glLoadMatrixf(proj); // Load the projection
For a more in depth look at how viewing and transformations work in OpenGL, I'd refer you to Chapter 3 of the OpenGL "Red Book". There they use glOrtho() to create and apply an orthographic projection.
Edit:
As datenwolf points out, bear in mind that the matrix elements in OpenGL are specified in column major order.
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