Can I use index buffer on PointCloudLayer

[usaken]

I am now using customized PointCloudLayer. I need to treat a large number of points, but I need to change the displayed points depending on the situation. I want to change points to show with index buffer. Can I use index buffer on PointCloudLayer ?
Index buffer means the following URL description:
https://webglfundamentals.org/webgl/lessons/webgl-indexed-vertices.html

[ibgreen]

@usaken Thanks for reaching out.

• Unfortunately, index buffers are not usable to control which rows are visible on instanced layers such as the point cloud layer. (they control only the non-instanced attributes).
• If you don't want to filter your instanced attributes, you could add an extra instanced attribute (e.g. pointVisible) and avoid rendering the point if they are not visible.
• You can avoid rendering by calling discard in the fragment shader, or generating "degenerate triangles" in the vertex shader.

[usaken]

Thank you for the answer and advices.
Using "if" statement for "discard" slows down processing.
I investigate about "degenerate triangles" and try to find another approach.

[ibgreen]

Using "if" statement for "discard" slows down processing.

Are you actually measuring GPU performance using Query objects or are you just guessing? We use the discard technique extensively and have not had issues.

The bigger perf hit is that you are still running the non-visible points through the shaders, not just the if statement itself (perhaps that is what you meant).

[usaken]

I tried to show over 20 million points with 1 draw call about 3 years ago. I used "if" for discard, and I found slow prosessing.
At that time, I thought it might have been a bad system design. Since then, I have avoided using "if" statement.
I am still beginner about WebGL, so now I am trying to consider various methods for rapid visualization.

[Pessimistress]

I'm not sure what you mean by "customized PointCloudLayer". If you are subclassing deck.gl's PointCloudLayer, then no, because the layer already uses an index buffer to draw each instance (circle). If you are writing your own primitive layer that draws GL_POINT, then sure, you can create an index buffer to select points.

It is hard to agree with a blanket statement such as "using if is bad". It greatly depends on how you write your shader.

Aside from experimenting with WebGL techniques, I also recommend that you investigate:

• The DataFilterExtension (use an additional buffer to show/hide instances)
• The TileLayer (slice your data into multiple layers that are shown/hidden dynamically)