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I'm trying to add a "sticker" on an equirectangular image.

The parameters I have are the angle of the sticker (yaw, pitch, roll), and its size in pixels, and the equirectangular image size (always a 2:1 ratio).

Example with this sticker (don't mind the background) :

enter image description here

If we put the sticker at the bottom of the sphere, the shader should be able to get something like this :

enter image description here

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    I suggest using raytracing. If I understand the wikipedia page on equirectangular projection correctly, you can easily get ray directions from image coordinates (ray_yaw = x / image_w * 2 * pi and ray_pitch = (y + image_h/2) / image_h * pi or something similar). Then for each ray you just need to find a point where (and if) it intersects your quad (the math should be relatively easy to google). Commented Mar 27, 2019 at 13:47
  • Shadertoy reference: shadertoy.com/view/MlfSz7 Commented Mar 28, 2019 at 9:33
  • @HolyBlackCat Thanks a lot I will have a look at ray tracing Commented Mar 28, 2019 at 13:20
  • @mlkn Thanks this link is very interesting. In the shader you linked, the image "covers" all the sphere, do you know how I could place the image at a certain place on the sphere, not on the whole object ? Commented Mar 28, 2019 at 13:23
  • when you know your sticker size and you want something simple you can experiment with texture projection on a sphere; created a little playground for experiment (hope it is useful) shadertoy.com/view/3dBSzy Commented Apr 1, 2019 at 18:55
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