08-17-2018, 04:56 PM
I don't think the SNES (or any other system of the era) had the ability to modify rendering parameters in the middle of a scanline. The time to traverse a single pixel is much shorter than the time to execute a single CPU instruction, and different TV standards use different timings, so the effect would be messed up in PAL/SECAM. So I think this is a dead end.
I guess the actual method is much simpler and uses the available tools: sprite overlapping and palette cycling with raster effect. If the circle shield is a 1-color sprite that shares palette with the main character, put the shield sprite behind the character sprite, and cycle that palette on each line, you have it.
As for the big scaling keyhole/circle transition, it should be interesting to load into an emulator and see what's happening. It acts as a vector layer, but I guess it's not the case, just what it looks like.
I guess the actual method is much simpler and uses the available tools: sprite overlapping and palette cycling with raster effect. If the circle shield is a 1-color sprite that shares palette with the main character, put the shield sprite behind the character sprite, and cycle that palette on each line, you have it.
As for the big scaling keyhole/circle transition, it should be interesting to load into an emulator and see what's happening. It acts as a vector layer, but I guess it's not the case, just what it looks like.