Feature request: Post processing with x-offsets for each raster line

[soegaard]

Back in the day most scrollers on 8-bit machines used the x-offset register. In order to render a given scanline the x-offset register was consulted and the rasterline was shifted a little in the horizontal direction. Using raster interrupts it was possible to change the value of the x-offset register at multiple positions along the screen.

I propose to add a post processing phase to mode-lambda. Instead of a register I propose to introduce a vector whose i'th element determines the x-offset of rasterline i.
To "hide" whatever has been scrolled out of view, the resulting image must be cropped (hence the famous border on the c64).

One approach to implement this:
https://en.wikibooks.org/wiki/OpenGL_Programming/Post-Processing

[jeapostrophe]

I'm willing to consider a pull-request, but I think that most of these effects can be done pretty well with multiple layers and the Mode7 system. If you wanted to implement it, I'd say it should be similar to have Mode7 works, although properly the thing to do is have an offset texture for the offsets (rather than a straight vector)

[soegaard]

I'm willing to consider a pull-request, but I think that most of these effects can be done
pretty well with multiple layers and the Mode7 system.

I might need to think harder about this - currently I can only think of making a sprite for each raster line.

For pull requests ... it will take a while before I have time to grok OpenGL. Maybe over the summer holiday. Feel free to close the issue. A wiki might be better for wish lists.

/Jens Axel