UniformBuffer addUniform

Questions
1

when i use UniformBuffer .addUniform,i find when i addUniform(‘a1’,1),addUniform(‘a2’,2),addUniform(‘a3’,1) ,and i console the uniform buffer the data will get five data , you can see this Babylon.js Playground
i think the four data are just aligned

pg
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LearnOpenGL - Advanced GLSL

2

Yeah, it’s just for alignment purposes, you can check how setUniform is implemented here :slight_smile: Babylon.js/uniformBuffer.ts at master · BabylonJS/Babylon.js (github.com)

3

where can i find rules about it,it’s puzzling to me https://www.babylonjs-playground.com/#MFGG10#2

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4

We follow the std140 rules. What exactly you don’t understand? :slight_smile:

5

pg2
Can you help me explain why they are different

6

The sizes of the uniforms? This depends on the type of data you’re going to pass to the buffer.

7

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8

Oh sorry, I hadn’t noticed the different orderings!

Basically, when filling out the uniform buffer, the addUniform function I linked earlier is going to make each member follow the std140 alignment rules ( OpenGL 4.5 (Core Profile) - June 29, 2017 (khronos.org))

In the 1, 2, 1, case, what happens is:

  1. Member with size 1 is added. The uniform buffer pointer is now at offset 1, which is a multiple of 1, so no padding is added.
  2. Member with size 2 is added. The uniform buffer pointer is now at 3, which is not a multiple of 2, so we pad to the nearest multiple, which is 4. Resulting in one 0 being added.
  3. Member with size 1 is added. The uniform buffer pointer is now at 5, which is a multiple of 1, so again, no need of padding.

In the 1, 1, 2 case, we have:

  1. Member with size 1 is added. The uniform buffer pointer is now at offset 1, which is a multiple of 1, so no padding is added.
  2. Member with size 1 is added. The uniform buffer pointer is now at offset 2, which is a multiple of 1, so no padding is added.
  3. Member with size 2 is added. The uniform buffer pointer is now at offset 4, which is a multiple of 2, so no padding is added.

That’s why one case has extra padding while the other doesn’t :slight_smile:

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9

thank you very much,i understand

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