经纹理opengles [英] Warp texture with opengles

问题描述

我正在使用opengles 2.0的Andr​​oid应用程序，我有相机preVIEW是这样的：

I'm making an Android app using opengles 2.0 and I have camera preview like this :

，并以此作为纹理。

and using this as a texture.

不过，我想简单地在红色圆环状的一侧弯曲。所以我想该部分从质地和裁剪的映射像一个长方形的形状。但我不知道，部分是究竟是如何农作物有什么方法做到这一点有效？

But I want simply warp in side of the red donut shape. So I'm trying to crop that part from the texture and mapping to a shape like a rectangular. But I don't know how exactly crop that part is there any ways to do that efficiently?

推荐答案

让我们假设我们有一个UV coordinages（S，T）的矩形R，其中S，T元素[0,1]。我们有一个中心C，一个内径里和外半径r给出环。

Lets assume we have a rectangle R with uv coordinages (s, t) where s,t element [0,1]. And we have the ring given by a center C, a inner radius ri and an outer radius ro.

如果我们想要的UV坐标（S，T）中的环的纹理坐标（s_tex，t_tex）映射，那么这可以通过使用以下的公式完成的：

If we want to map the uv coordinates (s,t) to coordinates in the ring texture (s_tex, t_tex), then this can be done by using the following formulas:

//alpha: angle
alpha = t * 2 * PI //maps the [0,1] range of t to [0, 2*PI] (circle)
//r: distance from the center 
r = ir + s * (or - ir) //maps s=[0,1] to [ir, or]

//d: direction from the center c
d = [sin(alpha), cos(alpha)]
//final coordinates
[s_tex, t_tex] = C + d * r

请注意，该 C，RI，RO 在环纹理贴图坐标被赋予。

Note, that C, ri, ro have to be given in texture coordinates of the ring texture.

根据你想拥有在环切（其中矩形的开始/结束映射到的位置），也可以是需要一个常数因子添加到阿尔法。此刻该因子为0时，这意味着该切口从C变为水平向右

Depending on where you want to have the cut in the ring (location where start/end of the rectangle are mapped to), it can be necessary to add a constant factor to alpha. At the moment this factor is 0, which means that the cut goes from C horizontally to the right.

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