* This is from the manual of AGDS (Adventure Game Development Toolkit) which contains a good deal of information about the AGI interpreter and its data formats. Translated from Russian by Vassili Bykov, vbykov@cam.org
(Translated from a russian document. The first part does not refer to the PICTURE resource format but gives a more detailed discussion of the picture commands used and the priority screen. The second part gives the format of a PICTURE resource).
This resource is used for static images (props), which create a background for animated objects programmatically associated with VIEW resources. (see I.2.2). The background is 160 pixels wide and 168 pixels high. Each pixel is painted using one of 16 colours. To create a 3D illusion, each pixel has another attribute: priority.
Priority determines the distance of each pixel from the viewer. Pixels which have the greater priority are considered to be closer and vice- versa. Priority is a value in the range between 0 and 15.
When an animated object (a VIEW resource) is displayed, it is drawn only on top of the pixels with the priority not greater than the object's. This creates an illusion of moving behind or in front of other objects.
Priority 4 is considered in the far back (objects cannot move behind it), priority 15 - the closest to the viewer (objects cannot move in front of it).
Priorities 0, 1, 2, 3 are special. Lines and areas of a PICTURE resource with priorities 0, 1, 2, 3 represent:
0 - unconditional barrier (border)
1 - conditional barrier
2 - alarm barrier
3 - water surface.
Picture resource is a sequence of commands produced by an editor of static images, Picture Manager (PM). Playing back the sequence draws an image used as the background of the action, and assigns required priorities to its pixels, thus creating a 3D scenery.
Please note that the drawing commands the picture-resource includes (described in section I.2.1) are created automatically by the Picture Manager (PM) as the artist draws the background he or she wants.
Let us look closer at these commands (see also the PM description).
Initially all pixels of the background are white and have priority 4. We can draw using the following colours:
| 0 - black | 8 - dark drey |
| 1 - blue | 9 - light blue |
| 2 - grueen | 10 - light green |
| 3 - cyan | 11 - light cyan |
| 4 - red | 12 - light red |
| 5 - magenta | 13 - light magenta |
| 6 - brown | 14 - yellow |
| 7 - light grey | 15 - white |
To change colours, this command is used. After it is executed, all the subsequent graphic commands draw using the colour set by the command.
This command is used if we have already drawn the image. Any graphic command issued after this one will not change the colour of image pixels the draw.
All graphic command issued after this one will set priority of the pixels they draw to the one set by this command.
Any graphic command issued after this one will not change priority of the pixels they draw.
Several graphic commands are used to draw images. There are several polyline drawing commands and a curved line command.
The first polyline command draws a line using the current colour and priority. The line consists of horizontal and vertical line fragments and begins with a vertical line.
Here is an example. First line fragment, always vertical:
(x,y)
|
|
V
(x,y1)
where x = horizontal coordinate, and y = vertical coordinate.
Since we draw a vertical line, X coordinate does not change. The next line fragment is horizontal, so now Y coordinate does not change:
(x,y)
|
|
V
*---------->(x2 ,y1)
(x,y1)
X is now x2, indicating that it is the second time it has changed.
In a similar fashion:
(x,y) (x2,y3)
| *----------->(x4,y3)
| ^
V |
*--------->*
(x,y1) (x2,y1)
There is no need to specify the whole sequence of coordinates (x,y), (x,y1), (x2, y1), (x2, y3), (x4, y3). Instead, it is enough to list only the coordinates that change, since we know the order of their changes (first - Y, then X, then Y again and so on). Thus, to describe this line it is enough to list (x, y, y1, x2, y3, x4).
It is this sequence of numbers that is used as the command operands.
The second polyline command is similar to the first but the first line fragment is horizontal.
(x,y) ------------>* (x1,y)
|
| ...
| |
V |
*-------------->*
(x1,y2) (x3,y2)
It is described by the sequence (x, y, x1, y2, x3, ...)
The third command draws an arbitrary polyline.
(x1,y1)
/\
/ \
/ \
/ \ ... (x3,y3)
/ \ /
(x,y) \ /
\/
(x2,y2)
It is described by the sequence (x, y, x1, y1, x2, y2, ...).
[I think "curve" is a actually a misnomer, this is just a polyline with each successive point specified relative to the previous one. --VB]
This is a variant of an arbitrary polyline command that draws a polyline made of very short line fragments.
The line goes from point (x,y) to the point (x1,y1), then to the point (x2,y2), etc.
The operands are x, y, dx1, dy1, dx2, dy2, ..., where dx(n) = x(n-1) - x(n), dy(n) = y(n-1) - y(n)
This command fills a closed area using the current colour and priority, beginning at a point inside the area. One command may fill one or more areas using pairs of coordinates within them.
The command works as follows:
1. If the current colour is set and is not 15 (i.e. not white), then the area to fill is the closed white area containing the argument point.
2. If the current colour is not set (was cancelled), the area to fill is the closed area of pixels with priority 4 containing the argument point.
Thus, it is impossible to repaint non-white areas or change priority if it is different from 4.
This command has two parts. The first specifies the parameters of the dots, the second - the dots themselves.
Dot parameters
Parameters in this part are:
1) a number from 0 to 7 giving the size of the dot.
2) if the size above is greater than 2, this parameter chooses whether the dot is drawn as a square (1) or as a circle (0).
3) selects whether the dot is opaque or "translucent", so that 1/3 of the pixels within the dot are left unchanged.
Dots
This part lists the coordinates where to draw the dots: x1, y1, x2, y2, ... where x(i), y(i) is the coordinate of the center of the dot.
If the dots are "translucent", a third parameter r(i) is required for each dot, determining the distribution of painted pixels within the dot.
This command ends the drawing, and is required at the end of a picture resource. See the description of PM editor for more information about graphics commands.
Picture resource is a sequence of graphics commands, execution of which creates the background pictures and assigns required priorities to its pixels.
A command is a one-byte operation code, optionally followed by one-byte operands. Commands are stored one after another.
Code F0. Operand: colour code
Initially all pixels of the background are white and priority 4.
Example: F0 0C - set current colour to bright red
All command following this command will use this colour for drawing.
Code F1.
Code F2. operand: priority
Example: F2 0D - set current priority to 13
Code F3.
The commands display polylines
Code F4. Operands: x,y,y1,x2,y3,x4,...
Draws a polyline using current colour and priority. The line consists of horizontal and vertical fragments, the first fragment is vertical.
Example: F4 28 32 64 78 32 29
Draws a rectangle in the centre of the screen
(40,50) (120,50)
*--------------------*
| |
| |
*--------------------*
(40,100) (120,100)
Code F5. Operands: x, y, x1, y2, x3, y4,....
Similar to F4 but the first line fragment is horizontal.
Example: F5 28 32 78 64 28 33
Draws the same rectangle.
Code F6. Operands: x,y,x1,y1,x2,y2,x3,y3,.....
Draws a polyline of random line fragments.
Example: F6 50 32 28 64 78 64 50 32
Triangle (80,50)
/\
/ \
/ \
(40,100) ------ (120,100)
Code F7. Operands: x,y, dd1, dd2, dd3,....
This is a variant of a random polyline drawing command which draws a polyline made of very short line fragments.
dd1, dd2, etc. mean packed in one byte two values dx and dy - offsets from the previous polyline vertex.
| Sx | x | x | x | Sy | y | y | y |
x x x - value between 0 and 6 - value of dx if Sx = 1; between 0 and 7 - if Sx = 0; y y y - value between 0 and 7 - value of dy;
Sx, Sy - if this bit is 0, the value is positive, otherwise it is negative.
Example: F7 4D 4D 60 06 E0 0D
(77,77) (83,77)
*------------*
| |
| |
| |
*------------*
(77,83) (83,83)
Code F8. Operands x1, y1, x2, y2, x3, y3,.....
Code F9. Operand: p.
Operand format:
| r | c | s | s | s |
s s s - a number between 0 and 7: the size of the dot
c - if the dot is larger than 2 and this bit is 1, the dot is drawn as a circle, otherwise - as a square.
r - if this bit is 1, the dot is "translucent", so that 1/3 of the pixels are not painted.
Other bits should be set to 0.
Code FA.
Operands: if in the previous F9 command bit r=0, then x1, y1, x2, y2, x3, y3,..... if r=1 r1, x1, y1, r2, x2, y2, r3, x3, y3,.....
x(i), y(i) - coordinates of the dot centre
r(i) - arbitrary value which determines the distribution of painted elements within a "translucent" dot.
Code FF.
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