1943 Sprites per Line (Core Update) (Patreon)

The 1943 object (sprite) engine was implemented in a custom chip so it wasn't possible to look inside. However, the pin names are similar to those used in other CAPCOM games so it was pretty much obvious how to hook it up to an already working object engine.

Ghosts'n Goblins is designed for a total of 96 objects (sprites) of which up to 24 may fall in the same horizontal line. With a 6MHz pixel clock and 16 pixels per object you can see how 24*16/6MHz = 64 microseconds, i.e. the horizontal line time.

Initially, when I was developing 1943 I couldn't see the ship cannons. It was one of this despair moments that often occur when developing. Then I decided to break the 96 object rule and let more in. Voilà, ship cannons were in place then. I was able to read more objects from the sprite DMA buffer using the same clock speed of 6MHz. The DMA buffer is a feature CAPCOM games used to copy the object data from main CPU RAM to a different buffer. 6MHz worked for me even with more sprites due to a different implementation of the DMA logic, which could operate in fewer clock cycles than the original. But I didn't change the 24-per-line limitation on the object count.

This month I have been working on Bionic Commando. This game has full schematics available and it follows on the school of previous CAPCOM games. The object engine supports 32 sprites per line and uses an 8MHz clock. Make the math: 32*16/8MHz=64 microseconds. So at 8MHz you can draw 6 extra objects.

With this new information and the impression I sometimes had that I was missing a bullet in 1943 I decided to increase the sprite count in 1943 to 32 per line. I think this is what makes sense.

Please get the new files using the update script for JT cores or directly from the binary repository.