In game paint brush with spreading. LoadRawTextureData() issues.

Hi everybody. This is my first question here ! My english is poor and forgive me for my typos/misspelling.

First of all, take a look on the result i want :

This is close to the final result, and the shader part is not merged yet, but that's a good visual to show what i want. The problem is : my CPU is totally overloaded. It looks smooth, but it's not when i have a great amount of points.

I'm going explain how i proceeded. It's a 2D game with sprites.

• When the game start, i create a texture from scratch, same size of the sprite it's on.

• Then when Input.MouseButtonDown, i cast a Ray and if it hits the sprite, i start a function which create a cricle.

• When a circle is drawn, the function will draw the same circle next frame with radius +1 until it reaches the bounds of the sprite.

What am i using?

I create my texture like that :

 texture = new Texture2D(spriteWidth, spriteHeight, TextureFormat.Alpha8, false);
 
 filling = new byte[spriteWidth * spriteHeight];
 
 for(int i=0; i<filling.Length ; i++){
     filling[i] = 0x00;
 }
 
 // Load data into the texture and upload it to the GPU.
 texture.LoadRawTextureData(filling);
 texture.Apply();
 
 // Assign texture to renderer's material.
 targetRenderer.material.mainTexture = texture;

I'm using a byte array to stock alpha (alpha8 texture) to minimize useless data.

But i read something that said actually, references are created in my array so it uses 4bytes to create a reference (same like pointers in c++, doesnt it?) to read the 1byte i've created? It sounds stupid. Is this true?

On a second hand, i've got spikes in the profiler when i apply my changes :

I've got an algotithm to get the pixels on texture to change inspired from this where i use C# part

It works well except the part where i apply changes on my texture. I'm doing like this :

     public void RefreshAndApplyTexture()
     {
         texture.LoadRawTextureData(filling);
         texture.Apply();
         targetRenderer.material.mainTexture = texture;
     }

It looks like LoadRawTextureData() burning my CPU everytime it's called because it had to refresh my whole array of pixels (around 1 million entries for 1k texture). I call it every frame i have to draw a cicle, for each point which draw a circle (with 10 origin points, it will be called 10 times). I don't know how to deal with this and i assume that i've reached c# limits... Or i'm just using the wrong way to do it.

Can you tell me how you would process for something like that?

This is my profiler :

And by the way, i think my 1 million entry array makes my garbage collector mad, using around 6ms every spike...

Thank you for reading this and i hope you will be able to help me.