Screen 4

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بواسطة Daemos

Paragon (2044)

صورة Daemos

14-02-2011, 20:22

So I have been fidling around with screen 4 for a long time but all I get is a nice yellow screen. I have to load the tiles in somewhere but I have no clue how. I also have to tell the VDP where these patterns have to go.

I just cannot find any good documentation on how to codewise display something on the Screen4. Hopefully anyone can shed some light on this?

I made a screen4 file and analysed it in the hope to find out how it works like it did for me in screen5 but I cannot figure it out...

Question: How does screen 4 codewise work and how does the screen 4 file work?

By now dropping in chunks of code will work in making me understand Wink

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بواسطة Edwin

Paragon (1182)

صورة Edwin

14-02-2011, 21:39

If you don't understand it, then you're probably not familiar with a tile mode. Access in asm is just like vram access in sc5, except that the data consists of three components:

1: 0000h, Pattern generator table. Defines 4 times 256 8x8 tiles of 8 bytes each (black and white)
2: 1800h, name table. Defines the 1024 tiles that are shown on screen. One byte per tile.
3: 2000h, Pattern colour table. Defines the colours for all tiles. Also 8 bytes each. One byte defines a foreground and background colour for each line.

As you might notice, 4 times 256 tiles is exactly 02000h bytes long, so the name table overlaps the pattern table by default. This is because screen 4 is in 192 line mode by default, so the fourth tile bank is unused and would only come into view while scrolling.

Also notice that basic sets the name table to three sequences of 0..255. This basically means that it assigns a different tile to each position. Basic does this because it works in graphics mode where it modifies the tiles on each drawing command. Games typically do the opposite and set the gfx tiles once and update the name table to move things around. Which is much less data to update. In fact, this table can be written to vram very efficiently as I have shown in an article here.

Experiment with data a bit. Use basic/vpoke to start with an initialised screen and check it out.

بواسطة ARTRAG

Enlighted (6923)

صورة ARTRAG

14-02-2011, 21:39

screen4 == screen 2 with multicolor sprites
This is why all documents refer to screen 2

بواسطة Lord_Zett

Paladin (807)

صورة Lord_Zett

14-02-2011, 21:46

and sc2 and sc4 are great modes diffuult to draw on but its possible look at daq lord of idar!

بواسطة Daemos

Paragon (2044)

صورة Daemos

14-02-2011, 22:08

oO So if I get this straight. Each tile is basicly not a bitmap divided out of 16 color pixels because you basicly decide in the generator table which pixel has color 1 and which pixel has color 2. Then in the pattern color table you define which color = 1 and which color = 2 on each line of the tile you draw...

How on heavenly name did they get those superb graphics in manbow if there is no control of the pixel itself within every tile.

بواسطة Edwin

Paragon (1182)

صورة Edwin

14-02-2011, 22:16

Excellent gfx designers. Tongue

بواسطة wolf_

Ambassador_ (10088)

صورة wolf_

14-02-2011, 22:36

You'll get used to drawing like that. Space Manbow has excellent tile graphics, that's true. But if you observe the in-game tiles sharply you'll notice only two colors per 8 horizontal pixels. And even if you think you see a third one, you're in fact looking at a neighboring tile. Sometimes a large enemy (boss level 1) uses an extra sprite overlay to fake an extra color. Viejo_archivero does this all the time, and I did it with the portraits of Dr.Pill and his feeble clients.

بواسطة commodorejohn

Expert (92)

صورة commodorejohn

14-02-2011, 22:41

Yeah, it pretty much just comes down to practice working with a tile designer for this. It's surprisingly doable, though - much more so than the two-colors-per-tile modes on machines like the Spectrum or C64. The big trick is to design or tweak existing designs around the tile boundaries so that you have as much control as possible.

بواسطة RobertVroemisse

Paragon (1325)

صورة RobertVroemisse

15-02-2011, 08:58

I am busy making graphics for screen 4 for some time now and at first I thought it was imposible to make a decent tile with the whole "two colors per 8-pixel horizontal line" thing, but I must say that the results are surprisingly nice. You just have to take certain difficulties/impossibilities such as diagonal lines and big circles into account when designing tiles. Check this URL out for some screen 4 examples:

http://www.twistedreality.nl/Deva-graphics-2-1.html

If you download an image from the site, load it in (for example) Photoshop and put a 8x8 grid over the image. This way, you can see the logic of screen 4.

بواسطة assembler

Champion (414)

صورة assembler

15-02-2011, 09:31

I am pleasingly surprised. I don't know that in screen4 you can change the palette. Is really impressive the result, in spite of the limitations of 2 colors for line.

Shocked!Shocked!Shocked!

بواسطة Metalion

Paragon (1622)

صورة Metalion

15-02-2011, 10:57

Check this URL out for some screen 4 examples:
http://www.twistedreality.nl/Deva-graphics-2-1.html

Really impressive !!!!
oOoOoO

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