How to get the Viewport Projection boundaries ? ( to get ScreenToWorldPosition )

Developing Cinder

sachaamm

How to get the Viewport Projection boundaries ? ( to get ScreenToWorldPosition )

in Developing Cinder • 3 years ago

Hi everybody ,

Im starting using cinder library and I would like to code a worldToScreen function which

gonna return me a vec3 ( woorld coordinate )

from the 2d Mouse position on a gl::scopedViewport

How I consider to solve this problem:

1- Normalize the mouse position from -1 to 1 from the viewport center

2- Calculate the right axis and up axis relative to the viewport camera

3- Calculate the projection boundaries ( in worldPos ) referring to the width and height of the camera render plane along

the target axis

4- Use the normalized mouse Position , the right and up axis relative to camera and projection boundaries to

get the woorld coordinate of the Screen position.

I read this topic , but it seems to be outdated :

https://forum.libcinder.org/#Topic/23286000000163070

My main question : is there an existing way from cinder to get the projection boundaries of the viewport camera ?

My goal is to generate raycasting in 3d Space to trigger colliders

I insert a picture to give me more clarity about my idea to code this algorithm

Any suggestion will be appreciated

Replies(4)

djtomservo

Re: How to get the Viewport Projection boundaries ? ( to get ScreenToWorldPosition )

3 years ago

Not sure, if this is helpful, but I recently implemented something similar using the topic (and a few other topics, but I don't remember which off the top off my head) you mentioned :) It IS written for pre 0.9.0, but some little changes made it work for me. Here's what I have:

void DustCloud::MouseSpawn(const vec2 &pMousePos, const CameraPersp & pCam)
{
auto ray = pCam.generateRay(pMousePos, getWindowSize());
float dist;
float testDist = mMaxDist - 0.1f; // Z of the plane we're testing against
if (ray.calcPlaneIntersection(vec3(0, 0, testDist), vec3(0, 0, -1), &dist)) {
auto rayPos = ray.calcPosition(dist); // This may be the droid you're looking for
}
}

Note that it's not specific to a custom viewport, so I'm not sure if this would be helpful for you, but it might get you pointed in the right direction. Anyone else, please feel free to correct this!

sachaamm

Re: How to get the Viewport Projection boundaries ? ( to get ScreenToWorldPosition )

3 years ago

Thanks for your precious help ! ! !

Im gonna try this , gl::viewport is optional ( I just have to normalize mousePosition to the viewport surface ) ... I will try your code like this :

void DustCloud::MouseSpawn(const vec2 &pMousePos, const CameraPersp & pCam)
{
auto ray = pCam.generateRay(pMousePos, getWindowSize());
float dist;
float testDist = target - pCam.getEyePoint(); // target is the position where the eye is looking on
if (ray.calcPlaneIntersection(vec3(0, 0, testDist), vec3(0, 0, -1), &dist)) {
auto rayPos = ray.calcPosition(dist); // This may be the droid you're looking for
}
}

paul.houx

Re: How to get the Viewport Projection boundaries ? ( to get ScreenToWorldPosition )

3 years ago

Have a look at gl::windowToObjectCoord() , which does exactly what you want if you pass an identity model matrix.

For ray casting, look at the CameraPersp::generateRay() method.

-Paul

sachaamm

Re: How to get the Viewport Projection boundaries ? ( to get ScreenToWorldPosition )

3 years ago

That's what exactly I was searching for , thanks for your time ! I will try your helpful line codes also tom for the raycasting

Greetings

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How to get the Viewport Projection boundaries ? ( to get ScreenToWorldPosition )

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