mirror of
https://github.com/tilleul/apple2.git
synced 2024-11-26 12:49:18 +00:00
Update apple2_hires.md
This commit is contained in:
parent
211c415650
commit
1295336f82
@ -269,9 +269,9 @@ The results are very informative. Let's zoom in a bit.
|
||||
![screenshot](img/apple2_hires_poke0-128detail.png)
|
||||
|
||||
The first line of pixels is black, corresponding to 0.
|
||||
POKEing 1 in the next line produced a violet dot in x=0, while POKEing 2 resulted in a green dot in x=1 and finally, POKEing 3 created two white dots, one in position 0 and the other in position 1.
|
||||
`POKE`ing 1 in the next line produced a violet dot in x=0, while `POKE`ing 2 resulted in a green dot in x=1 and finally, POKEing 3 created two white dots, one in position 0 and the other in position 1.
|
||||
|
||||
From these 4 POKE, we can already see that
|
||||
From these 4 `POKE`, we can already see that
|
||||
#### 1. Plotting is inverted compared to the order of the representation of a binary value.
|
||||
|
||||
| dec | binary | result |
|
||||
@ -302,4 +302,39 @@ To understand what color a pixel is going to be rendered, one must consider the
|
||||
|
||||
This might be summarised as the following:
|
||||
* if the pixel is off, it's rendered black except if both its neighbours are on, in which case it's rendered using the color of its neighbours' columns
|
||||
* if the pixel is on, it's rendered white except if both its neighbours are off, in which cas it's rendered using the color of his own column
|
||||
* if the pixel is on, it's rendered white except if both its neighbours are off, in which cas it's rendered using the color of his own column.
|
||||
|
||||
And we can continue our observations:
|
||||
#### 6. It's impossible to plot more than one pair of consecutive colored pixels: colored pixels are always odd in number
|
||||
#### 7. To plot only two consecutive colored pixels, they must be surrounded by two white pixels on one side and two black pixels on the other side
|
||||
#### 8. Single dot (then colored) pixels must be surrounded by two pairs of black pixels but the minimum distance between two single dot pixels of the same color is 3 black pixels. The minimum distance between two single dot pixels of different colors is 2 pixels.
|
||||
|
||||
Now what about values above 128 ?
|
||||
Let's edit line 20 of the previous program
|
||||
|
||||
20 FOR Y = 0 TO 160
|
||||
|
||||
![screenshot](img/apple2_hires_poke0-160detail.png)
|
||||
Yes ! New colors !
|
||||
|
||||
So, the 7th bit switches to a different color palette. Pixels in this palette follow the same rules as the previous palette. But we can add more observations.
|
||||
#### 9. A second palette is selected when the 7th bit (AKA the "hi-bit") is ON
|
||||
#### 10. Blue is on even columns and orange/red is on odd columns ... HEY WAIT !! LOOK CLOSELY !
|
||||
#### 11. Blue pixels are displayed in-between the columns of the violet/green pixels while red pixels are displayed in-between the columns of the green/violet pixels.
|
||||
|
||||
How weird is that ?
|
||||
Let's try this:
|
||||
|
||||
10 HGR: N=128: YY=0
|
||||
20 FOR Y = 0 TO 127
|
||||
30 A = INT(Y/64): REM A-ZONE
|
||||
40 B = INT( (Y - 64 * A) / 8): REM B-ZONE
|
||||
50 C = INT(Y - 64 * A - 8 * B): REM C-ZONE
|
||||
60 P = 8192 + A * 40 + B * 128 + C * 1024: REM STARTING ADDRESS IN RAM
|
||||
70 POKE P,YY+N
|
||||
80 N = 128-N: IF N=0 THEN YY=YY+1
|
||||
90 NEXT
|
||||
|
||||
![screenshot](apple2_hires_poke_colorsdetail.png)
|
||||
|
||||
What this does is plotting increasing values but every other line we add 128 to see the equivalent of the second palette.
|
||||
|
Loading…
Reference in New Issue
Block a user