Programming Discussion Thread

[Shonumi]

So for the past few days, I've been busy trying to emulate one of the trickier (in my opinion) parts of the GBA: Special Effects. Although it's just brightness increase/decrease along with alpha blending, there are just a lot of rules that determine which pixels from which layer is supposed to change. There are also 3 "windows" the GBA uses that can limit the area of the special effects (and do other things too, like completely disable rendering of a certain layer inside or outside its boundary). The 1st two are rectangular and box-like, the last basically uses sprites as a mask. It's not 100%, but it's mostly done. Here's a sampling with before and after side-by-side




This one is a simple alpha blending between two backgrounds, and it's necessary to see Kyogre though, else, the start screen just isn't cool at all. Ruby and Emerald do similar things with their start screens.




This is the intro for Megaman Zero 2, another display of alpha blending, this time affecting every background layer but the topmost one (used for the intro text, not shown here). Without alpha blending, all you get is a bunch of blocky sand. It's interesting to see how they got the fullscreen dust effect with the unblended original background.




More alpha blending! Just like the Pokemon games, but it's nice to see stuff working as it should.




Here's a good example of alpha blending in action. It makes for nice menus, after all.




Brightness increasing/decreasing doesn't get used for a lot of fancy effects. The obvious trick is to fade in and fade out (and many games do this manually anyway) or to make certain menus flash at a set rate. Sonic Advance uses them for lighting. I haven't peeked under the hood yet, but it looks like it's just making a window 1 pixel high per-scanline, and darkening everything outside that window, then adjusting the window size and position on the next line to dynamically get the slanted shape of the spotlight. It's a nice use of HBlank effects if that's really the case. A very similar effect happens in the intro (as Eggman gets the Chaos Emerald).




Just implemented this feature (most of it anyway) today. Some sprites only act as a mask, in that they aren't drawn on screen, but any area covered by them can be used for special effects or displaying certain background layers. The Pokemon games put these to good use. In this picture, there are actually two sprites of Zigzagoon on top of each other. The first is the mask, which isn't drawn, the second is the actual sprite that gets displayed. The masked pixels tells the LCD to start blending one of the backgrounds pixels with pixels from the next lowest layer (which happens to be the 2nd copy of Zigzagoon). It's a pretty cool way to make the status changing effects.

The focus for February has been all of these graphical changes. Once these are done, March is going to be all about APU emulation.