Disable Nes Sprite Limit on Real Hardware

While playing recently on my NES, I saw game characters beginning to flicker, and it reminded me how much things have changed since the 80s. Vintage hardware had real limitations, and artistic workarounds led to some familiar behaviors, like "sprite flicker" where characters sometimes flash quickly - a clever solution to maxing out the system's abilities.

When playing the NES, game characters sometimes flicker. Why?It's called "sprite flicker," and nothing's incorrect with your NES. Role of retro gaming's charm is the quirks of early technology. In this example, the express ability of the PPU (Moving-picture show Processing Unit of measurement). See why flicker happens.

Tabular array of Contents

• The Power of Retro 8-Bit Machines!
• The NES PPU, and Limited Retentiveness
• OK, So What Exactly is a Video Game Sprite?
• How Many Sprites Can Dance on the Caput of an NES PPU?
• Crowded Sprites Accept to Take Turns

Looking back from the present-day at retro gaming experiences can be a picayune confusing at times, because we're just so used to property total colour, advanced computing devices in our hands, and that seems normal to u.s.. We forget that back in the day, even though the systems seemed terribly cutting border at the fourth dimension (Play GAMES! On your TV! At dwelling, non the arcade!), the reality was that video game makers creating systems and cartridges for the home marketplace were pushing the edges of what could be done. They had to juggle performance and price, since there just was not a big market for highly capable, arcade-level experiences in the domicile, that necessarily cost a ton of money. In social club to bring fun and affordable gaming to the masses, they had to cleverly create fun on inexpensive hardware that normal people could buy.

Please note that this explanation needs to go into a fair bit of geeky tech, but it's all carefully explained for regular folk. If you don't desire all the foundational stuff, feel costless to bound down to "OK, And then What Exactly is a Video Game Sprite?"

The Power of Retro 8-Bit Machines!

The NES was built around a processor (the primary chip, or "brain" of the organization) called the MOS 6502. Introduced in 1975, it drove the explosion of home computers and video game systems that happened in the tardily 70s and into the 80s. Information technology was the heart of non only the NES, only the Atari 2600, the Apple II, and the Commodore 64 (it was in Commodore's VIC-20 and PET computers as well). The 6502 was so pop considering it was at a sweet spot of price and functioning, coming in at less that 1/6 the cost of similar chips from other makers, according to Wikipedia.

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This is really the 6502 out of my Commodore VIC-twenty. The 6502 in the NES is not labeled every bit a MOS 6502.

As snazzy equally the 6502 was at the time, it is an 8-fleck processor (also referred to equally viii-flake chip), and was the reason these were called 8-fleck machines. I know this term "8-bit" is usually thrown effectually, and so at present'due south a great time to get a quick agreement of why.

Computers speak "binary", that is, merely 1s and 0s. Each one or 0 is chosen a "bit." And so information is stored, moved, and processed in bits. In normal (decimal) counting, the "columns" in a multi-digit number go: ones, tens, hundreds, thousands, etc… and then that 57 is vii ones, and 5 tens. Each place moving toward the left has a value of x TIMES More the 1 to its right. In binary, each column is simply Ii TIMES MORE than the one to its left, so it'southward 1s, 2s, 4s, 8s, 16s, etc. So 8 bits all set to a value of 1 looks like 11111111, and is actually 255 in our normal decimal counting arrangement (1 one, 1 two, i iv, 1 eight, 1 sixteen, 1 xxx-two, 1 sixty-4, and 1 i-hundred-twenty-8 = 255). An viii-fleck processor tin can move things around for processing in 8-scrap chunks - that information technology is tin merely work with chunks whose value ranges between 0 and 255, or 256 different values (counting 0 as ane of them).

A series of 8 bits is likewise referred to as a byte. More on that in a 2nd.

The NES PPU, and Express Retentivity

By comparing, my current phone, a Samsung Galaxy S7 has a 64-bit bit, with 8 different cores in it (every bit opposed to the 1 core the 6502 had). It's besides a LOT faster, with four cores running at two,300,000,000 (2 billion, 300 million) cycles per second and 4 cores running at ane,600,000,000 (i billion, 600 million) cycles per second. Past dissimilarity, the 6502 in the NES runs a single core at 1,790,000 (one million, vii hundred ninety thousand) cycles per 2nd. And then the NES ran a LOT slower, only had one cadre, and had to move data around in 8-flake chunks (values between 0 - 255), versus a not-fifty-fifty-current mobile phone of today, which in addition to its speed and 8 cores working together at the same time, moves data around in 64-scrap chunks (values betwixt 0 - eighteen,446,744,073,709,551,616 - that's 18 quintillion, iv hundred 40 six quadrillion, seven hundred twoscore four trillion, seventy three billion, seven hundred nine million, five hundred 50 thousand, six hundred sixteen). That'south a lot less getting done with each pass back in the 8-fleck day.

Now not only were processors pricey, just retentiveness (RAM, or Random Admission Retentivity) was also. That meant the graphics processor in the NES (the Motion-picture show Processing Unit, or PPU) had a total working expanse (consummate RAM capacity) of 2K, or 2 Kilobytes, or 2,000 bytes.

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This is the bottom of the circuit board out of my NES console. The PPU is the chip outlined in scarlet. BONUS: The actual NES 6502 chip is the one outlined in yellow.

To envision that, sympathise that a single graphic symbol of text - just ane letter of the alphabet - normally uses i byte. Await at this snippet from the get-go folio of H.Grand. Wells' War of the Worlds to see how ridiculously short 2K really is.

OK, Then What Exactly is a Video Game Sprite?

Wikipedia says that the term "sprite" was offset used in reference to computer graphics at Texas Instruments. Following in the longstanding tradition of embedding fantasy literature concepts into computers (a byproduct of geek civilization, plain), an engineer used the term "sprite" to refer to a dissever bit of image information that was able to bladder effectually on top of the main screen prototype, independently from the background. This means that to make something motion onscreen, these independent, small image pieces could be used very efficiently, instead of having to redraw everything on the screen for each frame of animation. Efficiency means performance, which ways better gaming.

As for the fantasy lit connection, sprites are mythical creatures akin to fairies. The conceptual tie-in to something small that magically floats around inside a scene makes sense, then. At present you know, and can impress your friends.

How Many Sprites Can Dance on the Caput of an NES PPU?

But await - there'due south less! While the NES Flick Processing Unit has a total of 2K (2,046 to be exact) bytes of RAM, it only has 256 bytes of storage for sprites - the little graphic pieces used to make our animated onscreen items. At present expect at this chopped bit of the above State of war of the Worlds text to come across how much 256 bytes is, if 1 alphabetic character is 1 byte. Yikes. That's non much. In the game world, it meant 64 8X8 pixel sprite graphics - the top left quadrant separated out hither from this Super Mario sprite sheet:

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The upper left quadrant (outlined in green) shows 64 sprites from Super Mario Bros (NES). Notation how they look jumbled, considering they are but pieces. It takes 8 sprites to make Mario (run into below).

While the PPU will hold 64 sprites, it is further express past the fact that but viii sprites can exist on a TV scanline together, due to how the retentiveness space is gear up. A scanline is a horizontal line of pixels in the total screen epitome the NES sends to the TV.

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Green indicators testify individual horizontal scanlines in Batman for the NES.

Go on in mind that a sprite and an onscreen character are not at all the same thing. Sprites are 8-pixel-by-8-pixel graphical pieces that can be animated and separately floated "in front of" the background. A good example to demonstrate the stardom is that Mario, from Super Mario Bros is 16 pixels wide, past 32 pixels tall, requiring a total of viii sprites to put him onscreen. Feeling the squeeze nonetheless?

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Dark lines divide upwardly the eight 8 pixel X 8 pixel sprites, and light lines divide up the individual pixels making upward the sprites.

So and then, since Mario is 2 sprites wide, any given scanline he's on will already have 2 sprites on it. Add in some other animated sprites, and you'll quickly striking your ceiling of 8-to-a-scanline.

Crowded Sprites Accept to Accept Turns

The hardware can't show anything across viii sprites to a scanline, so it doesn't. Still, if game developers just permit this happen, your character, a bad guy, or some portion thereof would simply disappear. Poof. He's still there, but totally invisible. Obviously, this would create serious play problems, then clever video game programmers came upwardly with a compromise. They go on track of all the sprites that should show on a given scanline, and trade off betwixt them:

• FRAME 1: evidence sprites 1-viii of x
• FRAME 2: show sprites two-9 of 10
• FRAME iii: evidence sprites 3-x of 10
• FRAME 4: evidence sprites 1 & 4-x of ten
• FRAME 5: show sprites 1-2 & v-10 of 10

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Blocks 1-x across each row correspond the total number of sprites, with the orangish outline indicating the 8 sprites the PPU is showing during that frame. Each row of blocks represents a frame of our 5 frames of blitheness. You tin can clearly run into how this "shifting" of which sprites show and which don't creates a rolling coma, which is the flicker you see.

This way, the sprites that are left invisible keep changing, so yous have a kind of rolling blackout of two sprites (in this instance of ten sharing a scanline) for each frame of onscreen animation, instead of a full blackout on annihilation beyond 8. The outcome is the familiar shimmering flicker you've seen.

Next time you play, observe when sprites crossing into busy scanlines starts things flickering. Discover how flickering gets heavier equally a scanline gets busier, and the list of sprites beyond eight grows. Note that this heavy flicker but occurs in some special cases, since game developers were very careful to minimize flicker as much every bit possible. It'due south not an optimal behavior, and makes the simulated reality suspension down, feeling less solid. Annotation also how games volition oft continue sprites separated from each other, and so they don't share scanlines - like the animated items on different platforms on the same screen in a "platformer" game like Super Mario Bros.

Now you lot understand the limitation, and the inventive smoke-and-mirrors tricks used to hide them. Happy gaming!

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