How to use RenderTexture for drawing custom textures?

Graphics Shaders & Materials
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1

I’m trying to figure out how can I use RenderTexture to draw a custom brush in the coords where another object collide but I don’t know how to modify my renderTexture using a custom brush

Also I want to change gradually my renderTexture very slow from it’s current state to transparent to erase whatevery I draw passed a few seconds/minutes

As I know I must use blit to apply the changes in the renderTexture but I’m not understanding this

And I don’t want to use setpixel/setpixels because it use CPU instead of GPU and i need good performance

2

A render texture just captures what a camera is seeing.

Here’s my lotto scratcher: