I have a simple question, in scene graph implemention. A scene node record transform info relation parent scene node. As we know, The full transform matrix is built by Trans(local) * Trans(parent) * Trans(root). The local transform matrix is create from translation, scale and rotation, and the order is SRT, scale * rotation * translation. But now I have a model, it is not modeled at its geometry center. So before apply rotation to rotate the model, we need to apply a local space translation, translate the origin to geometry center first, then we can rotate around any axis. In this case, we need a transform order translate * rotate, not the default rotate * translate.
Question is in Ogre like engine, how to rotation scene node which attaches the model as i describe above.
I have solved myself. First, create a scene node which is used to translate to model center. The model is attached to this scene node. Then do whatever you want, the scene node we created before is a child of any other normal scene node.
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My Three.js app has a static perspective camera looking on (0,0,0). How can I find the x/y coordinates in the y=0 plane of the corners of the camera's viewfield? The app covers the entire web browser, so this would correspond to the corners of the web browser. I want to render 3D models between those corners.
I want to render 3D models between those corners.
Just having the mentioned corner points is not sufficient to determine whether the user can see an object or not. The camera also has a near/far plane and also a perspective which you should take into account.
I suggest you use a different workflow and create an instance of THREE.Frustum based on the camera's projection screen matrix. The code looks like so:
const frustum = new THREE.Frustum();
const projScreenMatrix = new THREE.Matrix4();
projScreenMatrix.multiplyMatrices( camera.projectionMatrix, camera.matrixWorldInverse );
frustum.setFromProjectionMatrix( _projScreenMatrix );
You can then use methods like Frustum.intersectsObject() or Frustum.intersectsSprite() to determine whether 3D objects are in the view frustum or not.
This is actually the way WebGLRenderer performs view frustum culling.
In three.js, I want to use the SimplifyModifier to simplify a model to several different degrees. The problem is that the geometry for the model contains attributes for normals, skinIndex, skinWeight, and position. The modifier removes all attributes other than position, and in the end, I am left with a black, static geometry. Is there any way I can programmatically create low polygon versions of my buffer geometry which also have these attributes modified as well?
For realising a scrollable text container (using own bitmap fonts that are basically small sprite meshes) I am using local clipping planes.
When my text container moves the clipping planes are updated according to the global boundaries of my container.
This works perfectly except for fast movements. In this case the clipping planes are slightly delayed behind the container making the text shine through where it shouldn't.
My first thought was that the necessary code for updating the clipping planes might cause the delay.. but when I use apply this order:
1. update the text box position
2. update the clipping planes
3. render()
the delay still exists
Is the reason maybe located in the threejs framework in how the actual clipping is applied?
Here's a small code snippet that shows how I compute my upper clippin plane using two helper meshes. The one is a plane that is positioned orthogonally on my text object (red plane in the picture). The other one is a THREE.Object3D that is positioned in the middle of the upper edge for computing the right plane constant.
// get the world direction of a helper plane mesh that is located orthogonally on my text plane
var upperClippingPlaneRotationProxyMeshWordDirection = _this.upperClippingPlaneRotationProxyMesh.getWorldDirection();
// get the world position of a helper 3d object that is located in the middle of the upper edge of my text plane
var upperClippingPlanePositionProxyObjPosition = _this.upperClippingPlanePositionProxyObj.getWorldPosition();
// a plane through origin which makes it easier for computing the plane constant
var upperPlaneInOrigin = new THREE.Plane(upperClippingPlaneRotationProxyMeshWordDirection, 0);
var dist = upperPlaneInOrigin.distanceToPoint(upperClippingPlanePositionProxyObjPosition);
var upperClippingPlane = new THREE.Plane(upperClippingPlaneRotationProxyMeshWordDirection, dist*-1);
// clipping plane update
_this.myUpperClippingPlane.copy(upperClippingPlane);
picture showing the text object with clipping plane helpers
I found the reason for the delay. In my matrix updating code I only used updateMatrix() on the text object when it moves. To make sure that its child objects including the helper meshes update instantly I had to call updateMatrixWorld(true), this makes sure that the clipping planes are computed correctly
I'm working on a driving simulation in Three.js using height map data from the planet Venus.
GitHub repo here: https://github.com/hypothete/venus-walk
Here's how the simulation works so far:
In a hidden scene, a camera called the globeCamera moves at a fixed height over a sphere textured with the Venus height map. You can see this happening in the lower left viewport in my picture. The globeCamera renders its view to a WebGLRenderTarget to be used as a local height map. The result is in the second viewport in the middle left.
In the visible scene, a plane mesh called the terrainMesh has its vertices displaced up and down in correspondence with the values from the local height map. This gives the illusion that a vehicle placed in the center of the plane is moving across a surface when actually we're just updating the plane's vertices from the movement of the globeCamera.
Since I know the rotation of the globeCamera, I can pass that value to my fragment shader to rotate the terrainMesh's rock texture with the height map.
How can I offset the rock texture's position so that texture units translate with the terrain as well? I've tried tracking the globeCamera's offset as a 2D vector and adding that to the rotated UV in the fragment shader, but my results were inconsistent. Thanks for your help.
After modifying my main camera's projection matrix, the ScreenPointToRay method that use ray casting begin to fail, so the method which detect touched object use raycast fail too. Is there any way to use ScreenPointToRay method with a custom camera projection matrix?
If you made a custom camera projection matrix, then you probably know where is the user pointing to, how about casting a ray yourself and not using the helper?
If you have a problem with translation of the cursor to world position, there is a good approximation - take four angles on approxiamtely the edges of your camera's viewpoint (top of the viewport horizontal center, left of the viewport vertical center etc.) and interpolate between them.