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Question by BelfegnarInc · Nov 02, 2014 at 04:12 PM · cameramatrixprojection

Reproduce WorldToViewportPoint function

Hello. I am trying to reproduce native camera.WorldToViewportPoint function, for projecting mesh vertices to viewport. I write colors to texture for visualisation. So, here is what i've tried:

1) Transform vertex position to worldspace using TransformPoint, then use WorldToViewport

 Vector3 v = goTransform.TransformPoint(vertices[i]);
 Vector3 pos = mCamera.WorldToViewportPoint(v);
 texture.SetPixel((int)(pos.x*textureSizeW), (int)(pos.y*textureSizeH), Color.white);

And as result, everithing is fine:

alt text

2) Calculate ModelViewProjection matrix and multiply it with vertex position.

 Matrix4x4 M = goTransform.localToWorldMatrix;
 Matrix4x4 V = mCamera.worldToCameraMatrix;
 Matrix4x4 P = mCamera.projectionMatrix;
 Matrix4x4 MVP = P*V*M;
 
 Vector3 pos = MVP.MultiplyPoint(vertices[j]);
 texture.SetPixel((int)(pos.x*textureSizeW), (int)(pos.y*textureSizeH), Color.white);

But result is wrong:

alt text

3) After reading this answer, I've added this part to my code:

 if (d3d) {
     // Invert Y for rendering to a render texture
     for (int i = 0; i < 4; i++) {
        P[1,i] = -P[1,i];
     }
     // Scale and bias from OpenGL -> D3D depth range
     for (int i = 0; i < 4; i++) {
        P[2,i] = P[2,i]*0.5f + P[3,i]*0.5f;
     }
 }

But result are still wrong. Could you help me to understand what am I missing? Thanks

1.png (394 B)
2.png (394 B)
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avatar image notmschneider · Dec 29, 2014 at 03:37 AM 0
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i am stuck with the same problem. did you solve it?

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Answer by Paulius-Liekis · Dec 29, 2014 at 02:49 PM

Maybe you need pos /= pos.z, i.e. applying projection?

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Answer by sirshelley · Feb 05, 2016 at 02:50 AM

When you use Multiplypoint it converts it to clipping space so too correct:

screenpos.x being your (Projection matrix* View matrix)Multiplypoint(vector) //clipping to 1,1 Vector3 scPos= new Vector3(screenPos.x + 1f, screenPos.y + 1f, screenPos.z + 1f) / 2f; // viewport into screen scPos = new Vector3(screenPos.x Screen.width, screenPos.y * Screen.height, screenPos.z);

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