Improvement for seamless drawing

[brainfoolong]

To draw seamless tiles could get a good workflow boost if we actually can see repeated tiles directly in the canvas. The preview window on the top right is very good, but for pixel exact tiling it is not that handy.
I came up with this idea, i tried to implement it for myself but don't have enough time to dig deeper in the code.
Here is a concept of what i imagine, this is perfect for seamless drawing, at least for me :)
What do you think?
Edit: You should only be able to draw in the main center, the other's are only copied for visualization.

[juliandescottes]

Thanks for submitting this idea. Looks like it could be really useful.

I made a quick prototype based on your mockup on the following branch: https://github.com/juliandescottes/piskel/tree/feature-tiled-drawing

Feel free to pull and give it a try. Needs a lot of cleanup and performance tests but I really expected this to perform a lot worse than it does.

[brainfoolong]

Oh wow, awesome. That's exactly what i've meant. For me it doesn't have any performance impact, works pretty well here. Tested with newest FF and Chrome. Thanks for the insanely quick reply.

[epicabsol]

That looks amazingly helpful! It would also be nice to toggle the opacity of the preview images to 100% to see how the sprite will look more accurately.

[juliandescottes]

Could be nice for the next release. Assigning myself.

Todo:

• figure out if we should repeat the layers preview
• rename "repeated preview" checkbox to "seamless drawing" or something like that
• bind the feature to the preference mentioned above

[juliandescottes]

@epicabsol good idea as well, I'll file a separate issue for this.