CODEWITHSUNDEEP
androidopengl-es
kju
kju

Reputation: 123

Warp texture with opengles

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

enter image description here and using this as a texture.

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?

Upvotes: 1

Views: 288

Answers (1)

BDL
BDL

Reputation: 22157

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.

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

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

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.

Upvotes: 1

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