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Question by LuisCRSousa · Feb 19, 2018 at 09:42 PM · mappingprojectionperspectiveprojectionmatrix

Projetion Mapping on Unity

Hi! I'm trying to do a perspective transformation from a render texture to a real world plane but so far unsuccessfully. This is what I have now using Image Warp from asset store: alt text This tool distorts the image (mesh), but perspective transformation is not equal to distortion as the following image shows. alt text

The question is, how can I make a perspective transformation for projection mapping? Opencv have this kind of tools, Unity have projection Matrix, but documentation says nothing about that..

screen-shot-2018-02-19-at-213310.jpg (275.5 kB)
28116951-1664005013642481-1646658161-n.png (24.5 kB)
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Answer by OliverUmbrella · Nov 25, 2019 at 02:24 PM

There was a site with an algorithm. But it is available on webarchive: https://web.archive.org/web/20160402083111/http://www.bitlush.com/posts/arbitrary-quadrilaterals-in-opengl-es-2-0

  1. Calculate the q value for each vertex (when you move the screen coordinates of one vertex, you have to recaluclate the q values) as described on the page

  2. Create a list of Vector4 texture coordinates strq for each vertex

  3. strq.x = s * q, where s is the ordinary s texture coordinate

  4. strq.y = t * q, where t is the ordinary t texture coordinate

  5. strq.z is not used

  6. strq.w = q

  7. Pass the list of the Vector4 texture coords via Mesh#SetUVs(int channel, List uvs)

  8. In the fragment shader calc: u = texcoord.x / texcoord.w; v = texcoord.y / texcoord.w

  9. return tex2D(_MainTex, float2(u, v))

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