使用鼠标将像素绘制到BufferedImage - 提高性能

I switched from programming in Processing to Java and right now, I am trying to translate some techniques to pure Java programming language. It seems that my code is lagging sometimes and it is also slower than in my Processing sketches. Did I get something wrong? How could I improve my code? Would this kind of calculation also work gpu computation, maybe in lwjgl?I switched from programming in Processing to Ja