How to deal with transparent textures and depth in three.js? - javascript

My scene contains a number of planes with PNG textures. First, my problem was the transparent parts of the texture hiding other objects behind it. Then I found the workaround by disabling depth testing and depth buffer writing, which however introduced another problem: at certain distances and angles, objects that are behind, render over those that are in front of them:
Now, I'm a relative newcomer to 3D programming, but through reading other SO answers, such as:
Three.js / WebGL - transparent planes hiding other planes behind them
Transparent textures behaviour in WebGL
Three.js - depthWrite vs depthTest for transparent canvas texture map on THREE.Points
I think I understand that depth and transparency are a difficult issue in general. However, I am not sure what the right direction from here is. Should I manually calculate the distance of the objects from camera, then tell three.js to render them from farthest to closest? Would that fix the issue? Or is there another general solution?

Related

Is it more performant to use a sprite or a BufferedGeometry in Three.js?

I'm rewriting a legacy visualization built several years ago with an older version of Three.js. The visualization is ~20k 2D circles (nodes from a graph) drawn on a screen with positions and coloring already determined.
There's no animation involved other than when interaction occurs (zooming, clicking, etc). The previous author used sprites for the circles (nodes) to show different states (node selected: glowing effect, node hidden: transparent, etc)
I've been able to successfully reproduce much of the visualization using CircleBufferGeometry instead of a sprite.
I know this is potentially too vague a question, given it might be too specific to my use case, but I'm wondering if anyone has any insight into whether it's more performant to render ~20k sprites or ~20k CircleBufferGeometry with Three.js / webgl.
Thanks!
CircleBufferGeometry will have many more vertices per entity than a sprite would since sprites should be drawn with gl.POINTS ( one point == one vertex ). Your vertex shader would process more vertices with the circle than it would with a sprite.

Profiling Threejs app

I have a webgl application, I've written using threejs. But the FPS is not good enough on some of my test machines. I've tried to profile my application using Chrome's about:tracing with the help from this article : http://www.html5rocks.com/en/tutorials/games/abouttracing/‎
It appears that the gpu is being overloaded. I also found out that my FPS falls drastically when I have my entire scene in the camera's view. The scene contains about 17 meshes and a single directional light source. Its not really a heavy scene. I've seen much heavier scenes get render flawlessly on the same GPU.
So, what changes can I make in the scene to make it less heavy, without completely changing it? I've already tried removing the textures? But that doesn't seem to fix the problem.
Is there a way to figure out what computation threejs is pushing on to the GPU? Or would this be breaking the basic abstraction threejs gives?
What are general tips for profiling GPU webgl-threejs apps?
There are various things to try.
Are you draw bound?
Change your canvas to 1x1 pixel big. Does your framerate go way up? If so you're drawing too many pixels or your fragment shaders are too complex.
To see if simplifying your fragment shader would help use a simpler shader. I don't know three.js that well. Maybe the Basic Material?
Do you have shadows? Turn them off. Does it go faster? Can you use simpler shadows? For example the shadows in this sample are fake. They are just planes with a circle texture.
Are you using any postprocessing effects? Post processing effects are expensive, specially on mobile GPUs.
Are you drawing lots of opaque stuff? If so can you sort your drawing order so you draw front to back (close to far). Not sure if three.js has an option to do this or not. I know it can sort transparent stuff back to front so it should be simple to reverse the test. This will make rendering go quicker assuming you're drawing with the depth test on because pixels in the back will be rejected by the DEPTH_TEST and so won't have the fragment shader run for them.
Another thing you can do to save bandwidth is draw to a smaller canvas and have it be stretched using CSS to cover the area you want it to appear. Lots of games do this.
Are you geometry bound?
You say you're only drawing 17 meshes but how big are those meshes? 17 12 triangle cubes or 17 one million triangle meshes?
If you're geometry bound can use simplify? If the geometry goes far into the distance can you split it and use lods? see lod sample.

Three.js drop shadow

I was wondering if there's a way to project a shadow without have a "ground" plane where project it.
I'd like to do that because the camera can be moved around the object and would be ugly see it pass through the ground.
I'm using Three.js latest-version with the WebGl renderer.
Yes this is possible by applying ShadowMaterial to the plane geometry. This material can receive shadows and is completely transparent. so you just position the plane geometry at the desired location in the scene and you are good to go. check out this. https://threejs.org/docs/#api/en/materials/ShadowMaterial
This is technically impossible, you could write a shader that renders the shadow on a transparent plane, that way you would not notice it when the "camera" goes through the plane, only when it goes through the shadow itself.
To do so you can lerp between the shadowratio and a transparent black or white in the pixel shader and then set the corresponding blending states on the rendering context.

Transparency Face-Jumping?

I've been working on a WebGL project that runs on top of the Three.js library. I am rendering several semi-transparent meshes, and I notice that depending on the angle you tilt the camera, a different object is on top.
To illustrate the problem, I made a quick demo using three semi-transparent cubes. When you rotate the image past perpendicular to the screen, the second half of the smallest cube "jumps" and is no longer visible. However, shouldn't it still be visible? I tried adjusting some of the blending equations, but that didn't seem to make a difference.
What I'm wondering is whether or not this is a bug in WebGL/Three, or something I can fix. Any insight would be much appreciated :)
Well, that's something they weren't able to solve when they invented all this hardware accelerated graphics business and sounds like we'll have to deal with this for a long while.
The issue here is that graphic cards do not sort the polygons, nor objects. The graphics card is "dumb", you tell it to draw an object and it will draw the pixels that represent it and also, in another non-visible "image" called zbuffer (or depthbuffer), will draw the pixels that represent the object but instead of color it will draw the distance to the camera for each pixels. Any other objects that you draw afterwards, the graphics card will check if the distance to the camera for each pixel, and if it's farther, it won't draw it (unless you disable the check, that is).
This speeds up things a lot and gives you nice intersections between solid objects. But it doesn't play well with transparency. Say that you have 2 transparent objects and you want A to be drawn behind B. You'll need to tell the graphics card to draw A first and then B. This works fine as long as they're not intersecting. In order to draw 2 transparent objects intersecting then the graphics would have to sort all the polygons, and as the graphics card doesn't do that, then you'll have to do it.
It's one of these things that you need to understand and specifically tweak for your case.
In three.js, if you set material.transparent = true we'll sort that object so it's drawn before (earlier) other objects that are in front. But we can't really help you if you want to intersect them.

Background with three.js

Can anybody help me with three.js?
I need to draw background, something, like a THREE.Sprite, but it neet to be UNDER any 3d object, that will draw later. I have a camera, that can be move only on Z axis.
I tryed to use:
cube mapping shader - PROBLEM: artefacts with shadow planes, it's unstable draw
THREE.Sprite that dublicate camera moving - PROBLEM: artefacts with shadow plane - it have a edge highlighting OR drawing only other spirtes without objects.
HTML DOM Background - PROBLEM: big and ugly aliasing in models.
What can I try more? Thanks!
You could maybe try drawing in several passes, i.e. making a first render of the background scene to a buffer, and then a second one over the first "buffer". Maybe using the buffer as background (painting it in 2D with an orthographic projection, and disabling depth buffer writes in that pass).
I haven't tried it myself with three.js, but that's how I'd do that with "traditional" OpenGL.
If you want a "3d" background i.e. something that will follow the rotation of your camera, but not react to the movement (be infinitely far), then the only way to do it is with a cubemap.
The other solution is a environment dome - a fully 3d object.
If you want a static background, then you should be able todo just a html background, i'm not sure why this would fail and what 'aliasing in models' you are talking about.

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