SceneKit - Fix screen frame to camera edges - xcode

I'm working on a app that renders a 3D scene that simulates a real space into an iPhone making its screen become a hollow box, as seen in the sketch below:
(note the camera position order down below)
The problem is on how to calculate the camera parameters to make the box look real fixed to the screen edges.
Is this feasible through SceneKit?

In this configuration the camera's zNear plane corresponds to the screen of the iPhone. From that you can can derive a z position from the camera's field of view and the screen's width (see here).

Related

THREE.js Orthographic camera position not updating after *dolly* with OrbitControl

I'm using THREE.OrbitControls to dolly a THREE.OrthographicCamera. But, even thought the ortho camera renders correctly as repositioned, all that is updating on the orthographic camera is the 'zoom' property. Even after calling camera.updateProjectionMatrix(). Do I need to manually update the 'position' property of the camera based on the updated 'zoom' property? I want to display its position in my UI after dollying it.
(Note, this is a rewrite of my other question,THREE.js Orthographic camera position not updating after zoom with OrbitControl, in which I thought I was zooming with the OrbitControl but was actually dollying. Sorry about this).
Dollying in/out with an ortho cam would have an unnoticeable effect. With ortho cams there is no perception of proximity because it has no perspective. All objects appear the same in size regardless of distance from the lens because the projection rays are all parallel. The only difference you'd notice is when the objects get clipped because they're past the near or far plane.
So, the decision was made that scrolling with OrbitControls would change the zoom of the camera, narrowing in/out of the center.
If you want to force the camera to move further/closer of its focus point, you could just translate it back/forth in the z-axis with:
camera.translateZ(distance); A (-) distance would move it closer, and a (+) distance would move it further from its focus point.

Creating a magnifying-glass effect in three.js WebGL

I'm working with an orthographic view in three.js/WebGL renderer, and I want a magnifying glass that tracks with the user mouse. I'm looking for the best way of doing this that's efficient.
When working with html5 canvas raw commands, this was easy: I simply defined a circular clip region, zoomed my coordinates, and re-drew the whole scene. With 3d objects, it's less obvious how do to it.
The method I've found so far is to do the following:
Define a second camera that looks into the zoomed region. Set the orthographic clip coordinates to be small so that it doesn't need to do much work
Create a THREE.WebGLRenderTarget
Tell the renderer and all my line textures that the resolution is about to change
Render the scene into the RenderTarget
Add a CircleGeometry as a MeshObject at the spot at the mouse position (in world coordinate but above the rest of the scene, close to the camera). Call this the lens.
Give the lens the WebGLRenderTarget as a texture.
Go back to my default camera, reset all my resolution parameters, and redraw the scene with the 'lens' object added.
This works (see image below) but I'm worried about parts of it:
I have to render twice per frame
Lines don't draw well, because the resolution problems. I have to keep track of all materials that need to know screen resolution and update all of them twice per screen render.
Related problems:
I want to overlay some plot axes on top of this, and possibly gridlines. These would change as the view pans. I'm not sure if I should make these 3d objects, or do it in a 2d canvas context I lay overtop.
I want to overlay some plot lines, and have them show up sensibly in the zoomed view. "Sensible" here is hard to figure out: I don't want them too fat in the zoomed view, but I also don't want to scale them up as much as the image detail (which is being rendered as a texture onto Plane objects behind).
This is a long post, but I'm still new to three.js and looking for good ideas.

How to offset target position in ThreeJS controls

I am using ThreeJS's OrbitControls so that when an object in my scene is clicked, the camera travels close to it and and starts orbiting around it. I'm just moving the controls.target position, camera position and setting controls.autoRotate = true.
The clicked object gets centered on screen, which is nice, but sometimes I need to show a text covering up to 50% of the bottom area of the screen, and then the selected objects gets hidden by it. So, I'd need to somehow offset the rotation center up a bit.
Perhaps another way of asking this is that I need to change the center of rotation so that it is NOT the center of the screen (or the center of the renderer canvas)
I've tried moving the target up but, of course, then the camera doesn't orbit around the selected 3D object but around an empty space close to it. Any idea on how to proceed?
Many thanks!
I finally got the desired results following the comments in this other thread:
by using camera.setViewOffset

three.js is there a way to detect the clip position or when the far clip has been reached based on zoom?

For three.js, is there a way to detect the clip position or when the far clip has been reached based on the camera zoom? Or, some way to convert camera zoom to the same units as the camera near and far clip float values?
It looks like the .zoom field on PerspectiveCamera only affects the camera's field of view and not the near or far clip planes. Here is where it's used when calculating the camera's projection matrix:
https://github.com/mrdoob/three.js/blob/master/src/cameras/PerspectiveCamera.js#L192
You can see how the zoom factor is affecting the field of view by using the getEffectiveFOV function:
https://threejs.org/docs/#api/en/cameras/PerspectiveCamera.getEffectiveFOV

getting sprites to work with three.js and different camera types

I've got a question about getting sprites to work with three.js using perspective and orthogonal cameras.
I have a building being rendered in one scene. At one location in the scene all of the levels are stacked on top of each other to give a 3D view of the building and an orthogonal camera is being used to view it. In another part of the scene, I have just the selected level of the building being shown and a perspective camera is being used. The screen is divided between the two views. The idea being the user selects a level from the building view and a more detailed map of that selected level is shown on the other part of the screen.
I played around with sprites for a little bit and as far as I understand it; if the sprite is being viewed with a perspective camera then the sprite's scale property is actual it's size property and if a sprite is being viewed with an orthogonal camera the scale property scales the sprite according to the view port.
I placed the sprite where both cameras can see it and this seems to be the case. If I scale the sprite by 0.5, then the sprite takes up half the orthogonal camera's view port and I can't see it with the perspective camera (presumably because for it, the sprite is 0.5px x 0.5px and is either rounded to 0px (not rendered, or 1px, effectively invisible). If I scale the sprite by say 50, the the perspective camera can see it (presumably because it's a 50px x 50px square) and the orthogonal camera is over taken by the sprite (presumably because it's being scaled by 50 times the view port).
Is my understanding correct?
I ask because in the scene I'm rendering, the building and detailed areas are ~1000 units apart on the x-axis. If I place a sprite somewhere on the detail map I need it to be ~35x35 pixels and when I do this it works fine for the detail view but building view is overtaken. I played with the numbers and it seems that if I scale the sprite by 4, it starts to show up on my building view, even though there's a 1000 unit distance between the views and the sprite isn't visible with the perspective camera.
So. If my understanding is correct then I need to either use separate scenes; have a much bigger gap between views; use the same camera type for both views; or not use sprites.
There are basically two different ways you can use sprites, either with 2D screen coordinates or 3D scene coordinates. Perhaps scene coordinates are what you need? For examples of both, check out the example at:
http://stemkoski.github.io/Three.js/Sprites.html
and in particular, when you zoom in and zoom out in that demo, notice that the sprites in-scene will change size, while the others do not.
Hope this helps!

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