Shader uniforms capacity

[Zyko0]

Hello, I read some opengl about the limitations of passing a huge amount of data as uniforms to a shader.
But in my application I do have specific needs of describing a scene to be rendered on GPU, I read that I do have two options:

• Creating a texture containing my data
  Using a texture with ebiten, I don't know of a way to keep the precision of my float values.

• Using UBO (https://www.khronos.org/opengl/wiki/Uniform_Buffer_Object) but I don't know if it's too much opengl-related, or if it can be implemented/accessed in Ebiten.

As an example, let's say I have a single shader rendering a scene by computing 800 complex shapes analytically (described as vec2 position, vec2 size for example), this would require too many uniforms, if the scene is rendered like:

DrawRectShader(screenWidth, screenHeight, sceneShader, optsUniformsOf800shapes)

Currently I'm going with:

for _, e := range entities {
   DrawRectShader(e.Width, e.Height, entityShader, optsWithFewUniforms)
}

But this is really gpu intensive, and shouldn't require multiple shader invocations.
It also goes against the automatic batching logic, which can't apply here..

How should I solve this problem with these constraints using Ebiten ?

Thanks in advance ! 😄

[hajimehoshi]

Disclaimer: I'm not an expert shading-language programmer.

This depends on how much uniform data you need, but in general, using a texture as a data array is the only way to go so far.

Creating a texture containing my data
Using a texture with ebiten, I don't know of a way to keep the precision of my float values.

Yes, the precision might matter. Could you give an example of the shapes data you want to pass to the shader?

[Zyko0]

I'd split a 16bit integer into two 8bit integers and then use 2 floats for 1 value.

Oh yeah that's a good idea, I believe this would keep enough precision, thank you !

Nice! I hope this works with any GPUs.

Yes, if everything is encoded into a texture, I guess it should work anywhere !

I'll try going this road, thanks again !

I'm just wondering how much will "cost" all this texture encoding, as well as imgTextureAt() calls in shader, if data changes at each Draw

[hajimehoshi]

Note: If we want to treat 'unnormalized' textures whose elements are [0-255] instead of [0.0-1.0], GL_EXT_texture_integer seems available in OpenGL, but I don't think this is available in WebGL.

https://www.khronos.org/registry/OpenGL/extensions/EXT/EXT_texture_integer.txt

[hajimehoshi]

I'm just wondering how much will "cost" all this texture encoding, as well as imgTextureAt() calls in shader, if data changes at each Draw

The cost is ReplacePixels to update the pixels, and that's all I guess.

[Zyko0]

Yeah maybe bandwith and texture lookup with a bunch imgTextureAt() to decode the scene at each Draw/Fragment pass if there is a lot of data.
But I will give a try ! 😅

[hajimehoshi]

Yeah maybe bandwith and texture lookup with a bunch imgTextureAt() to decode the scene at each Draw/Fragment pass if there is a lot of data.

Ah, that sounds an issue. But however you passed the data, it'd be inevitable to access the data.