Planes
Whether you have just come from BASIC To C, Starting to learn more about the
Amiga System or Whatever. Sooner or later you are going to want Bobs and/or
Images in your Source Code (for such things as Icons, Graphics, etc) perhaps
because loading a TITLE SCREEN (IFF) with your program each time is not
pratical, etc.
Some people manage to get Bobs/Images into their Source Code by `Cutting and
Pasting' other peoples Source Code - Others prefer to Read the relevant Amiga
Books. However, Regardless of the method, for those people who do manage to
have Bobs/Images in their source code, some of them will only have limited
use of those Bobs/Images simply because what they have programmed only covers
the Basic functions/routines. Why? A couple of reasons are; 1) They simply
`Cut and Pasted' the source code as mentioned above, thus, perhaps the source
code did not have any Information attached to it and 2) The Amiga Books, etc
they read were a bit too Technical/Jargonised, thus, they could not take
advantage of all the Non-Basic functions.
The Articles I shall be writing for `DoubleClick' over the next few Issues
will try to explain, hopefully in an Easy To Understand way, some of the
Amiga Functions/Routines and/or some Programming Routines/Ideas.
Here are 3 examples of the kind of thing I will be trying to explain....
* Article 1 (Not released yet) - Bits and Bytes.
Confused about ANDing, ORing, XORing or Binary, Hex, etc?
This will explain the Basics of Bits and Bytes - I.e What a Byte
is. INT. Binary. Hex. etc.
* Article 2 (You are looking at it!) - PLANES.
* Article 3 (Not released yet) - Scrolling.
Have you ever wondered `How do I write a Continuous Vertical Scroll'?
If so, this Article is for you.
This will explain one way of making a Continuous Horizontal Scroll and
explain one way of making a Continuous Vertical Scroll.
PLANES - Of the Graphics kind.
--------------------------------
Written By: John White.
-------------------------
Here is a definition of One PLANE, with a Width of 8 Pixels and an Height
of 8 Pixels. It has Two Colours in it:
11110000
11110000
00001111
00001111
11110000
11110000
00001111
00001111
How do we know the plane has only two colours in it? Simple. Each Pixel
has a Binary Value. For example. In the above, each pixel with the binary
number Zero represents the colour zero and thus has a binary value of zero.
Each pixel with the binary number One represents the colour one and thus
has a binary value of one. Because the binary numbering system only allows
us to enter a zero or one binary number it means a plane can only have
two colours in it.
In the above, zero would represent the Background colour and one would be
the Ink colour. Thus, the Image [] would be drawn.
[]
[]
[]
-----------------
More Colours...
-----------------
So if the binary numbering system only allows us to enter a zero or one,
how do we go about getting More Colours into our Image?
To get more colours we simply put one plane on top of the other, treating
them as if they are Transparent, and then add up the binary numbers of a
certain Pixel Position.
Here is an example of 2 Planes, thus, making up 4 Colours...
00000000 00000000
00000000 00000000
00001111 00000000
00001111 00000000
00000000 <- Plane 1. 11110000 <- Plane 2.
00000000 11110000
00001111 00001111
00001111 00001111
...If you look at the pixel in Top Left Corner of both planes and add up
their binary numbers you will get 0 + 0 = Binary Value 00000000
(Colour Zero).
If you now look at the pixel in the 3rd Line Down/6th Across of both planes
and add up their binary numbers you will get 1 + 0 = Binary Value 00000001
(Colour One).
You may of thought that the colour one above should of been calculated as
1 + 0 = 10 (Binary Value 00000010). The reason why it wasn't is because we
had to follow 2 rules. 1) Binary Values go from Right-To-Left and not
left-to-right. 2) Planes go in the order of plane 1 First, plane 2 Second,
etc. Thus, colour one had to be added up as follows....
-------- Plane 1 - Its binary number was 1. If it was 0 it would still
| have been put into this binary position simply
| because, regardless of its binary number, it is
| the First plane.
00000001 <- Binary Value.
|
|
--------- Plane 2 - Its binary number was 0. If it was 1 it would still
have been put into this binary position simply
because, regardless of its binary number, it is
the Second plane.
Colour Two can be found by looking at the pixel in the 5th Line/8 Across of
both planes and then adding up their binary numbers. You will get 0 + 1 =
Binary Value 00000010, which is 2.
Colour Three can be found by looking at the pixel in the 8th Line/8 Across
of both planes and then adding up their binary numbers. You will get 1 + 1 =
Binary Value 00000011, which is 3.
The whole Image will look like this....
Colour Zero on this line.
[] <- Colour One.
Colour Two -> []
[] <- Colour Three.
Note: In the above, the pixel positions mentioned to find the colours were
there to guide you. There were other pixel positions I could of used.
(I.e The Image has 8 pixels in colour one, two and three - not just
the one pixel I mentioned for colour one, two and three).
------------------------
Even More Colours?!...
------------------------
Hopefully, the above has been clear enough for you to understand what has
been explained? However, sometimes when learning we don't register what
has been said/explained straight away - because we may need time to digest
the information - and sometimes we need a few more examples just to make it
absolutely clear to us what is being explained. Therefore, I shall give one
last example (of 8 Colours). You should, after the following example, either
understand the Basics of Planes or still be at a total loss!....
00001111 00000000 00000000
00001111 00000000 00000000
00001111 11111111 00000000
00001111 <- Plane 1. 11111111 <- Plane 2. 00000000 <- Plane 3.
00001111 00000000 11111111
00001111 00000000 11111111
00001111 11111111 11111111
00001111 11111111 11111111
Looking at the pixel in the 8th Line Down/6th Across of all three planes and
then adding up their binary numbers you get 1 + 1 + 1 = Binary Value 00000111
which is 7 (Colour Seven).
Looking at the pixel in the 6th Line Down/6th Across of all three planes and
then adding up their binary numbers you get 1 + 0 + 1 = Binary Value 00000101
which is 5 (Colour Five).
The Plane layout for Colour Five is as follows....
-------- Plane 1 - Its binary number was 1. If it was 0 it would still
| have been put into this binary position simply
| because, regardless of its binary number, it is
| the First plane.
00000101 <- Binary Value.
||
||
|--------- Plane 2 - Its binary number was 0. If it was 1 it would still
| have been put into this binary position simply
| because, regardless of its binary number, it is
| the Second plane.
|
|
------ Plane 3 - Its binary number was 1. If it was 0 it would still
have been put into this binary position simply because,
regardless of its binary number, it is the Third plane.
If we had 4 Planes, Colour 8 would be...
Binary Value 00001000, which is 8.
||||
||||--- Plane 1.
|||
|||---- Plane 2.
||
||----- Plane 3.
|
|------ Plane 4.
...Colour 9 would be....
Binary Value 00001001, which is 9.
-----------------
Using Planes...
-----------------
Plane Data is mostly used for Graphics, although you could use it for other
purposes. Our purpose for plane data is an Image....
Copy the Plane Data to Memory, using a Procedure...
copyPlanesIntoChipMemory([%00000011111100000011111100000000,
%00000011111100000011111100000000,
%00000011111100000011111100000000,
%00000011111100000011111100000000,
%00000000000011111111111100000000,
%00000000000011111111111100000000,
%00000000000011111111111100000000,
%00000000000011111111111100000000])
...Now set up the Image Object/Structure...
myImage:=[X, The X (Left) screen position.
Y, The Y (Top) screen position.
WIDTH, The WIDTH, in Bits (Pixels), of your Image.
The Maximum width is 24 Bits (Pixels). The last 8 Bits,
in each line of a PLANE, is reserved for the system - Thus,
making up a 32 Bit Line.
Note: This applies to Image Data only, as far as I am
aware. Bob Data can use the full 32 Bits per Line.
HEIGHT, The number of, 32 Bit, Lines in each PLANE.
PLANES, The number of Planes in an Image.
DATA, A Pointer to your Image Data (The PLANE Data).
PlanePick, See Below.
PlaneOnOff, See Below.
NIL]:image NIL is a Pointer to the Next Image object. For this
example and article it is (set to NIL) not pointing
to another Image.
...From here, you would simply use the - DrawImage() - command, when you
needed to.
-----------------------------
PlanePick and PlaneOnOff...
-----------------------------
Lets pretend that I have just opened a Screen with 16 colours in it and I
have a 2 Plane (4 colour) Image. To select which colours to use with my
image I simply use the PlanePick and PlaneOnOff functions like so....
PlanePick PlaneOnOff Colours selected
%0011 %0000 0 1 2 3
%0011 %0100 4 5 6 7
%0011 %1000 8 9 10 11
%0101 %0000 0 1 4 5
%0101 %0010 2 3 6 7
%0110 %0000 0 2 4 6
%0110 %0001 1 3 5 7
With PlaneOnOff set to 0, PlanePick simply allows you to pick the Screen
Planes you wish to use with your image. However, with a PlaneOnOff value
other than 0, PlanePick and PlaneOnOff combined may allow your image much
more flexibility with the colours. So, with example one above, you are
simply saying pick Screen Plane 1 (which holds colours 0 and 1) and also
pick Screen Plane 2 (which holds colours 2 and 3). Whereas example four is
saying pick Screen Plane 1 (colours 0 and 1) and also pick Screen Plane 3
(which holds colours 4 and 5).
This is all well and good, but what happens when you want to use colours 2,
3, 6 and 7 for example? Well, as example 5 shows from example 4, you simply
set PlaneOnOff to %0010 - which sets plane 2 to all ones, thus, giving you
colours 2, 3, 6 and 7.
The PlaneOnOff function simply sets any planes not receiving image data to
either all Ones or all Zeros. Only those planes not set in PlanePick are
used in PlaneOnOff.
You may be wondering how we got to use colours 2, 3, 6 and 7 by setting
PlaneOnOff above to %0010? Well, if we go back to example four we shall
see why....
Example 4 PlanePick Combinations - %0000 = 0
%0001 = 1
%0100 = 4
%0101 = 5
With Example 5, because Plane 2 is set by PlaneOnOff (Which means we must
include Plane 2 in all of our PlanePick Combinations), the combinations for
Example 5 (from example 4) become...
%0010 = 2
%0011 = 3
%0110 = 6
%0111 = 7
...We could not get combinations for 0, 1, 4 or 5 because, as said above,
PlaneOnOff means we had to include Plane 2 in our combinations, which has
the value of 2 of course - Thus, 2 was the smallest number combination we
could use.
If you look at examples 6 and 7 you will see the same thing happens between
them as what happened with examples 4 and 5.
Basically, once you have set the PlanePick and PlaneOnOff functions the only
reason for changing them would be in those cases where it would be easier
changing them rather than physically changing your image data.
I hope this Article has been of use to you - John White.