Exactly. I'm pushing pixel pattern at Virtual DMA cycle using BIT $x0 or BIT $x0x0 instruction as @phaeron already explained.
Also I've implemented 240-hires scanlines bugfix using your algorithm.
So, as you can see I didn't invent anything, but just sit and did the job
@phaeron Thanks a million for your "Altirra Hardware Reference Manual" - I studied its ANTIC scanline diagrams for different modes. It's very helpful.