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Chapter 11
Block Transfer Routines
256 Fastgraph User's Guide
Overview
The Fastgraph routines described in this chapter copy rectangular blocks
between areas of video memory, between virtual buffers, between conventional
memory and video memory, or between conventional memory and virtual buffers.
Such routines are sometimes called Blit or BitBlt routines in other
literature. Block transfers are useful in many graphics applications, but they
are especially important in animation.
Fastgraph provides several types of block transfer routines, each
optimized for its specific purpose. Because these routines are often used in
speed-critical contexts, they do not perform clipping. If needed, clipping can
generally be done at the application level by adjusting the block coordinates
to fit within the clipping region.
This chapter will discuss Fastgraph's block transfer routines in detail.
The information presented here, combined with the video page, virtual buffer,
and image management routines of the previous three chapters, will provide the
tools we need for the animation techniques presented in the next chapter.
Full Page Transfer
Fastgraph's simplest block transfer routine is fg_copypage, introduced in
Chapter 8. The fg_copypage routine transfers the entire contents of one video
page to another. The first argument is the number of the source video page,
and the second argument is the number of the destination video page. The pages
may be physical, virtual, or logical video pages. If both the source and
destination pages are logical pages, the pages must exist in the same type of
memory. For example, you cannot copy a logical page in extended memory to a
logical page in conventional memory. The fg_copypage routine always works with
video pages, even if a virtual buffer is active.
Example 11-1 illustrates the use of fg_copypage in a 320x200 color
graphics mode. The program displays the word "test" in the middle of the
visual page (page 0) and then uses fg_allocate to create a virtual video page
(page 1). The virtual page is needed in case the program is running in a video
mode with only one physical page. Next, the program uses fg_copypage to
transfer the visual page contents to page 1. After waiting for a keystroke,
the program erases the visual page, waits for another keystroke, and copies
the contents of page 1 back to the visual page. It then releases the virtual
page and exits.
Example 11-1.
#include <fastgraf.h>
#include <stdio.h>
#include <stdlib.h>
void main(void);
void main()
{
int new_mode, old_mode;
fg_initpm();
Chapter 11: Block Transfer Routines 257
new_mode = fg_bestmode(320,200,2);
if (new_mode < 0 || new_mode == 12) {
printf("This program requires a 320 ");
printf("x 200 color graphics mode.\n");
exit(1);
}
old_mode = fg_getmode();
fg_setmode(new_mode);
fg_setcolor(7);
fg_rect(0,319,0,199);
fg_setcolor(9);
fg_locate(12,18);
fg_text("test",4);
fg_waitkey();
fg_allocate(1);
fg_copypage(0,1);
fg_erase();
fg_waitkey();
fg_copypage(1,0);
fg_waitkey();
fg_freepage(1);
fg_setmode(old_mode);
fg_reset();
}
Byte Boundaries
Video memory, like standard random-access memory, is divided into units
called bytes. In text modes, each byte holds either a character or an
attribute. In graphics modes, each byte of video memory holds one or more
horizontally contiguous pixels. If two adjacent horizontal pixels are stored
in different bytes, then we say a byte boundary exists between the two pixels.
The number of pixels per byte depends on the video mode being used, so
the location of the byte boundaries also depends on the video mode. That is, a
byte boundary in a CGA graphics mode is not necessarily a byte boundary in a
VGA graphics mode. The following table summarizes the number of pixels per
byte of video memory and the byte boundary sequences for each supported
graphics video mode. Notice that any horizontal coordinate whose value is a
multiple of 8 is always a byte boundary, regardless of the video mode.
mode pixels horizontal coordinates
number per byte of byte boundaries
4 4 0, 4, 8, 12, ... , 316
5 4 0, 4, 8, 12, ... , 316
6 8 0, 8, 16, 24, ... , 632
9 2 0, 2, 4, 6, ... , 318
11 8 0, 8, 16, 24, ... , 712
12 4 0, 4, 8, 12, ... , 316
258 Fastgraph User's Guide
13 8 0, 8, 16, 24, ... , 312
14 8 0, 8, 16, 24, ... , 632
15 8 0, 8, 16, 24, ... , 632
16 8 0, 8, 16, 24, ... , 632
17 8 0, 8, 16, 24, ... , 632
18 8 0, 8, 16, 24, ... , 632
19 1 0, 1, 2, 3, ... , 319
20 1 0, 4, 8, 12, ... , 316
21 1 0, 4, 8, 12, ... , 316
22 1 0, 4, 8, 12, ... , 316
23 1 0, 4, 8, 12, ... , 316
24 1 0, 1, 2, 3, ... , 639
25 1 0, 1, 2, 3, ... , 639
26 1 0, 1, 2, 3, ... , 799
27 1 0, 1, 2, 3, ... , 1023
28 8 0, 8, 16, 24, ... , 792
29 8 0, 8, 16, 24, ... , 1016
Block transfer routines are often used in animation sequences requiring
high-performance graphics, so these routines must be as efficient as possible.
To this end, Fastgraph will force their horizontal pixel coordinates to byte
boundaries, which eliminates the need to process any pixels individually.
Fastgraph accomplishes this by reducing minimum horizontal coordinates to a
byte boundary and extending maximum horizontal coordinates to the last pixel
in a video memory byte. Since we are talking about pixel coordinates and not
character cells, the coordinate adjustment only occurs in graphics video
modes. Designing an application so block transfers occur on byte boundaries
might take additional planning, but it will be time well spent.
An example might best help explain this important feature. In the
EGA/VGA/SVGA 16-color graphics modes (modes 13 to 18, 28, and 29), byte
boundaries occur at every eighth pixel. Thus, when you use the block transfer
routines in these modes, Fastgraph reduces minimum x coordinates to the next
lower multiple of eight. Similarly, it extends their maximum x coordinates to
the next higher multiple of eight, less one pixel. That is, if a minimum x
coordinate is 10 and a maximum x coordinate is 30, Fastgraph will adjust these
values to 8 and 31 respectively. If the x coordinates were originally 8 and
31, Fastgraph would leave them unchanged.
In the MCGA and SVGA 256-color graphics modes (modes 19 and 24 to 27)
each pixel occupies a separate byte of video memory, so Fastgraph does not
need to adjust horizontal coordinates. However, in the XVGA graphics modes
(modes 20 to 23), some coordinate adjustment might be needed. The XVGA modes
store four pixels at each video memory address, one in each of four bit
planes. The bit plane number for a pixel whose horizontal coordinate is x is
given by the quantity x modulo 4. In XVGA modes, the source and destination
minimum x coordinates must reference pixels in the same bit plane. Put another
way, the relation
xmin_source modulo 4 = xmin_destination modulo 4
must be true. If it isn't, Fastgraph reduces the destination minimum x value
to the same bit plane as the source minimum x value.
Chapter 11: Block Transfer Routines 259
Dual SVGA Banks
Accessing video memory in SVGA graphics modes is controlled through a
banking scheme that maps contiguous 64KB blocks of video memory into a
segmented address space. In other words, referencing a specific byte in video
memory requires a bank number and an address within that bank. Some SVGA
chipsets provide separate read and write bank registers, while others perform
both operations through the same bank register.
If a chipset supports separate read and write banks, Fastgraph's block
transfer routines can copy the source region directly to the destination
region. However, chipsets that employ a single bank register require that
these routines copy the source region to an intermediate buffer and then copy
the buffer contents to the destination. This obviously makes a block transfer
operation slower on single-bank chipsets. Bit 3 of the fg_svgastat return
value will be set if the active SVGA chipset supports separate read and write
banks.
The "Hidden" Video Page
Some of Fastgraph's block transfer routines reference a video page called
the hidden page. The Fastgraph routine fg_sethpage defines which video page
will be used as the hidden page. This routine takes as its only argument an
integer value specifying the hidden page number. If you are using a virtual
video page for the hidden page, you must call fg_sethpage after allocating
that page. There is also a routine named fg_gethpage that returns the hidden
page number, as specified in the most recent call to fg_sethpage, as its
function value. The fg_gethpage routine takes no arguments.
Saving and Restoring Blocks
The next two block transfer routines we'll discuss are fg_save and
fg_restore. The fg_save routine transfers a rectangular region from the active
video page (as defined in the most recent call to fg_setpage) to the same
position on the hidden video page (as defined in the most recent call to
fg_sethpage). The fg_restore routine performs the complementary task -- it
transfers a rectangular region from the hidden page to the active page. Each
of these routines requires four arguments that define the coordinates of the
block to transfer, in the order minimum x, maximum x, minimum y, and maximum
y. In text modes, the coordinates are expressed as character space quantities
(rows and columns). In graphics modes, they are expressed as screen space
values (pixels), with the x coordinates extended to byte boundaries if
required. There are also world space versions of these routines named fg_savew
and fg_restorew available in graphics modes. The fg_restore, fg_restorew,
fg_save, and fg_savew routines always work with video pages, even if a virtual
buffer is active.
Example 11-2 demonstrates the use of fg_save, fg_restore, and fg_sethpage
in an 80-column text video mode. After establishing the video mode (note the
calls to fg_testmode specify that two video pages are needed), the program
fills the screen with text and then waits for a keystroke. Following this, the
program displays a small pop-up window prompting for another keystroke. After
waiting for the second keystroke, the program erases the pop-up window by
260 Fastgraph User's Guide
restoring the original screen contents, and then waits for yet another
keystroke before returning to DOS. We'll present the program now, and
afterward analyze it in detail.
Example 11-2.
#include <fastgraf.h>
#include <stdio.h>
#include <stdlib.h>
void main(void);
void main()
{
int row;
int old_mode;
char string[17];
fg_initpm();
old_mode = fg_getmode();
if (fg_testmode(3,2))
fg_setmode(3);
else if (fg_testmode(7,2))
fg_setmode(7);
else {
printf("This program requires\n");
printf("an 80-column display.\n");
exit(1);
}
fg_cursor(0);
fg_setattr(9,7,0);
for (row = 0; row < 25; row++) {
sprintf(string," This is row %2d ",row);
fg_locate(row,0);
fg_text(string,16);
fg_text(string,16);
fg_text(string,16);
fg_text(string,16);
fg_text(string,16);
}
fg_waitkey();
fg_allocate(1);
fg_sethpage(1);
fg_save(32,47,11,13);
fg_setcolor(1);
fg_rect(32,47,11,13);
fg_setattr(15,1,0);
fg_locate(12,33);
fg_text("Press any key.",14);
fg_waitkey();
fg_restore(32,47,11,13);
fg_waitkey();
Chapter 11: Block Transfer Routines 261
fg_freepage(1);
fg_setmode(old_mode);
fg_reset();
}
Example 11-2 first establishes the video mode and uses fg_cursor to make
the BIOS cursor invisible. It then executes a for loop that fills each row of
the screen with the phrase "This is row n", where n is the row number (between
0 and 24). Next, the program uses fg_allocate to create video page 1 as a
virtual video page. This is needed in case the program is running in mode 7,
which has only one true page (if the program is running in mode 3, fg_allocate
has no effect). The program then makes page 1 the hidden page by calling
fg_sethpage.
After setting up the hidden video page, but before displaying the pop-up
window, example 11-2 uses fg_save to save the current contents of the area
that the pop-up window will replace. The fg_save routine copies this region to
the hidden page. The program then displays the pop-up window in the middle of
the screen and leaves it there until a key is pressed. Following this, the
program uses fg_restore to replace the pop-up window with the original
contents of that region. This effectively erases the pop-up window and
restores the original screen. The program then waits for another keystroke,
after which it releases the virtual page and returns to DOS.
The next example, 11-3, is similar to example 11-2, but it runs in a
320x200 color graphics mode instead of a text mode. The main differences
between this program and example 11-2 are the use of 40-column text and the
use of screen space coordinates instead of character space coordinates in the
calls to fg_save, fg_restore, and fg_rect. Note that the call to fg_allocate
creates a virtual page if the program is running in modes 4, 9, or 19. In
modes 13 and 20, which respectively have four and eight physical pages,
fg_allocate does nothing.
Example 11-3.
#include <fastgraf.h>
#include <stdio.h>
#include <stdlib.h>
void main(void);
void main()
{
int row;
int new_mode, old_mode;
char string[21];
fg_initpm();
new_mode = fg_bestmode(320,200,2);
if (new_mode < 0 || new_mode == 12) {
printf("This program requires a 320 ");
printf("x 200 color graphics mode.\n");
exit(1);
}
old_mode = fg_getmode();
fg_setmode(new_mode);
262 Fastgraph User's Guide
fg_setcolor(7);
fg_rect(0,319,0,199);
fg_setcolor(9);
for (row = 0; row < 25; row++) {
sprintf(string," This is row %2d ",row);
fg_locate(row,0);
fg_text(string,20);
fg_text(string,20);
}
fg_waitkey();
fg_allocate(1);
fg_sethpage(1);
fg_save(96,223,88,111);
fg_setcolor(1);
fg_rect(96,223,88,111);
fg_setcolor(15);
fg_locate(12,13);
fg_text("Press any key.",14);
fg_waitkey();
fg_restore(96,223,88,111);
fg_waitkey();
fg_freepage(1);
fg_setmode(old_mode);
fg_reset();
}
A More General Block Transfer Routine
The fg_save and fg_restore routines each copy a rectangular region from
one video page to the same position on another video page. What if you need to
copy the region to a different position on another video page, or copy it
elsewhere on the same video page? Fastgraph provides a more general block
transfer routine named fg_transfer. The fg_transfer routine copies a
rectangular region on any video page to any position on any video page
(however, it cannot copy overlapping blocks on the same video page). Like
fg_save and fg_restore, fg_transfer works in text and graphics video modes. In
graphics modes, fg_transfer extends its x coordinates to byte boundaries if
necessary. The fg_transfer routine always works with video pages, even if a
virtual buffer is active (use fg_vbcut and fg_vbpaste to copy blocks between
virtual buffers and video pages, or fg_vbcopy to copy blocks between virtual
buffers).
The fg_transfer routine requires eight integer arguments. The first four
arguments define the region to copy, in the same order as expected by fg_save
and fg_restore. The next two arguments define the lower left corner of the
block destination, while the final two arguments respectively specify the
source and destination video page numbers. In short, fg_transfer copies the
specified region from the source page to the specified position on the
destination page.
Chapter 11: Block Transfer Routines 263
Example 11-4 is the same as example 11-2, but it uses fg_transfer rather
than fg_save and fg_restore. We have arbitrarily chosen to copy the region
overwritten by the pop-up window to the lower left corner of the hidden page
(page 1). When we copy this region back to the visual page, we copy from the
lower left corner of the hidden page back to the original position on the
visual page (page 0). This sequence is shown in the following diagram.
(11,32) (11,47) (22,0) (22,15)
first call
This is row 11 ------------> This is row 11
This is row 12 This is row 12
This is row 13 <------------ This is row 13
second call
(13,32) (13,47) (24,0) (24,15)
visual page (0) hidden page (1)
To copy one region to a new position and then back to its original position,
note how we make the fifth and sixth arguments in the first call to
fg_transfer the same values as the first and fourth arguments in the second
call. Similarly, the fifth and sixth arguments in the second call must be the
same as the first and fourth arguments in the first call. With all that out of
the way, here is example 11-4.
Example 11-4.
#include <fastgraf.h>
#include <stdio.h>
#include <stdlib.h>
void main(void);
void main()
{
int row;
int old_mode;
char string[17];
fg_initpm();
old_mode = fg_getmode();
if (fg_testmode(3,2))
fg_setmode(3);
else if (fg_testmode(7,2))
fg_setmode(7);
else {
printf("This program requires\n");
printf("an 80-column display.\n");
exit(1);
}
fg_cursor(0);
fg_setattr(9,7,0);
for (row = 0; row < 25; row++) {
sprintf(string," This is row %2d ",row);
fg_locate(row,0);
264 Fastgraph User's Guide
fg_text(string,16);
fg_text(string,16);
fg_text(string,16);
fg_text(string,16);
fg_text(string,16);
}
fg_waitkey();
fg_allocate(1);
fg_transfer(32,47,11,13,0,24,0,1);
fg_setcolor(1);
fg_rect(32,47,11,13);
fg_setattr(15,1,0);
fg_locate(12,33);
fg_text("Press any key.",14);
fg_waitkey();
fg_transfer(0,15,22,24,32,13,1,0);
fg_fg_waitkey();
fg_freepage(1);
fg_setmode(old_mode);
fg_reset();
}
Example 11-5 illustrates another use of the fg_transfer routine. This
example is functionally identical to example 10-10, but it uses fg_transfer
instead of fg_getmap and fg_drawmap. With the fg_transfer routine, we
eliminate the calls to fg_getmap and fg_drawmap, the two calls to fg_move, and
the 32-byte array needed to retrieve the block. As an added bonus, using
fg_transfer is much faster than the technique of example 10-10, although we
probably won't notice this gain with such a small block.
The block copied in example 11-5 is one row of four characters, so its
width in screen space is 32 pixels and its height is 8 pixels. Because the
block is in the upper left corner of the screen, the block boundaries are
xmin=0, xmax=31, ymin=0, and ymax=7. We want to move the block one-half
character cell (4 pixels) to the right and one row (8 pixels) down, so our
destination coordinates are x=4 (xmin+4) and y=15 (ymax+8). Note how the
program restricts itself to modes 19 and 20 to insure the block copy is not
affected by byte boundaries. Also, we are copying the block from one position
to another on the visual page, so both the source and destination pages are 0.
Example 11-5.
#include <fastgraf.h>
#include <stdio.h>
#include <stdlib.h>
void main(void);
void main()
{
int old_mode, new_mode;
fg_initpm();
Chapter 11: Block Transfer Routines 265
new_mode = fg_bestmode(320,200,1);
if (new_mode < 19) {
printf("This program requires a ");
printf("256-color graphics mode.\n");
exit(1);
}
old_mode = fg_getmode();
fg_setmode(new_mode);
fg_setcolor(9);
fg_text("text",4);
fg_waitkey();
fg_transfer(0,31,0,7,4,15,0,0);
fg_waitkey();
fg_setmode(old_mode);
fg_reset();
}
Example 11-6 shows yet another application of fg_transfer in a graphics
video mode. The program displays a rectangle in the upper left quadrant of the
screen and then centers the word "quadrant" inside the rectangle. After
waiting for a keystroke, the program uses fg_transfer to first copy the upper
left quadrant to the upper right quadrant. It then uses fg_transfer again to
copy the upper half of the screen to the lower half. The result of this is the
screen being filled with what was originally in the upper left quadrant.
Example 11-6.
#include <fastgraf.h>
#include <stdio.h>
#include <stdlib.h>
void main(void);
void main()
{
int new_mode, old_mode;
fg_initpm();
new_mode = fg_bestmode(320,200,1);
if (new_mode < 0 || new_mode == 12) {
printf("This program requires a 320 ");
printf("x 200 color graphics mode.\n");
exit(1);
}
old_mode = fg_getmode();
fg_setmode(new_mode);
fg_setcolor(7);
fg_rect(0,159,0,99);
fg_setcolor(9);
fg_locate(6,6);
fg_text("quadrant",8);
266 Fastgraph User's Guide
fg_waitkey();
fg_transfer(0,159,0,99,160, 99,0,0);
fg_transfer(0,319,0,99, 0,199,0,0);
fg_waitkey();
fg_setmode(old_mode);
fg_reset();
}
Block Transfer Routines for Virtual Buffers
Fastgraph's fg_restore, fg_save, and fg_transfer routines copy blocks
between physical or virtual video pages. Other routines are provided for block
transfers between virtual buffers and video pages, or between virtual buffers.
In our discussion of virtual buffers in Chapter 8, we described Fastgraph's
fg_vbcut and fg_vbpaste routines. Recall that fg_vbcut copies a block from the
active video page to the active virtual buffer, while fg_vbpaste copies a
block from the active virtual buffer to the active video page.
We'll now introduce another block transfer routine, fg_vbcopy, for
copying blocks between two virtual buffers, or to a non-overlapping position
in the same virtual buffer. The fg_vbcopy arguments are exactly the same as
those of fg_transfer, except the last two arguments reference the source and
destination virtual buffer handles instead of video page numbers. Example 11-7
is similar to example 11-6, but it uses fg_vbcopy to perform the two block
copy operations in a 320x200 virtual buffer (these were done with fg_transfer
in example 11-6). After this, it calls fg_vbpaste to display the virtual
buffer contents.
Example 11-7.
#include <fastgraf.h>
#include <stdio.h>
#include <stdlib.h>
void main(void);
#ifdef FG32
char buffer[64000];
#else
char far buffer[64000];
#endif
void main()
{
int handle;
int new_mode, old_mode;
fg_initpm();
new_mode = fg_bestmode(320,200,1);
if (new_mode < 0 || new_mode == 12) {
printf("This program requires a 320 ");
printf("x 200 color graphics mode.\n");
exit(1);
Chapter 11: Block Transfer Routines 267
}
old_mode = fg_getmode();
fg_setmode(new_mode);
fg_vbinit();
handle = fg_vbdefine(buffer,320,200);
fg_vbopen(handle);
fg_setcolor(7);
fg_rect(0,159,0,99);
fg_setcolor(9);
fg_locate(6,6);
fg_text("quadrant",8);
fg_vbcopy(0,159,0,99,160, 99,handle,handle);
fg_vbcopy(0,319,0,99, 0,199,handle,handle);
fg_vbpaste(0,319,0,199,0,199);
fg_waitkey();
fg_vbclose();
fg_setmode(old_mode);
fg_reset();
Blocks with Transparent Colors
The next block transfer routines we'll discuss are fg_tcxfer, fg_tcmask,
and fg_tcdefine. The fg_tcxfer routine is similar to fg_transfer in that it
copies a rectangular region from one position to another, but fg_tcxfer allows
you to treat one or more colors as transparent (the name fg_tcxfer stands for
transparent color transfer). In other words, any pixel whose color value is
defined to be transparent is not copied to the destination area. The fg_tcxfer
routine's arguments are the same as for the fg_transfer routine, but fg_tcxfer
has no effect in text video modes. Because fg_tcxfer must examine the color of
individual pixels, it is not nearly as fast as fg_transfer. The fg_tcxfer
routine always works with video pages, even if a virtual buffer is active (the
fg_vbtcxfer routine, described in the next section, provides transparent color
block transfers for virtual buffers).
You can use either fg_tcmask or fg_tcdefine to define which colors are
considered transparent in subsequent calls to fg_tcxfer. The fg_tcmask
routine's argument is an integer bit mask (specifically, a 16-bit mask) where
each bit indicates whether or not the color is transparent. For example, if
bit 0 (the rightmost bit) is set in the mask, then color 0 will be
transparent; if bit 0 is reset, color 0 will not be transparent. Because the
bit mask size is 16 bits, only the first 16 color values may be defined as
transparent using fg_tcmask.
Example 11-8 illustrates the use of the fg_tcxfer and fg_tcmask routines.
This program is similar to example 11-6, except the color of the word
"quadrant" (color 9) is defined to be transparent, and fg_tcxfer is used in
place of fg_transfer. Because color 9 maps to color 1 in the CGA four-color
graphics mode (mode 4), we must define both colors 1 and 9 to be transparent
(remember, fg_tcmask considers actual color values transparent, not color
indices). The bit mask passed to fg_tcmask thus will be 0000 0010 0000 0010
268 Fastgraph User's Guide
binary, or 0202 hex. This causes the word "quadrant" to appear in the
background color (color 0) instead of color 9 in the upper right, lower left,
and lower right quadrants.
Example 11-8.
#include <fastgraf.h>
#include <stdio.h>
#include <stdlib.h>
void main(void);
void main()
{
int new_mode, old_mode;
fg_initpm();
new_mode = fg_bestmode(320,200,1);
if (new_mode < 0 || new_mode == 12) {
printf("This program requires a 320 ");
printf("x 200 color graphics mode.\n");
exit(1);
}
old_mode = fg_getmode();
fg_setmode(new_mode);
fg_setcolor(7);
fg_rect(0,159,0,99);
fg_setcolor(9);
fg_locate(6,6);
fg_text("quadrant",8);
fg_waitkey();
fg_tcmask(0x0202);
fg_tcxfer(0,159,0,99,160, 99,0,0);
fg_tcxfer(0,319,0,99, 0,199,0,0);
fg_waitkey();
fg_setmode(old_mode);
fg_reset();
}
The fg_tcdefine routine expects two integer arguments -- one defining the
color number (between 0 and 255) and another defining the transparency state
associated with that color. If the state is zero, the specified color will be
opaque (non-transparent). If it is any other value, the color will be
transparent. In the previous example, we could use fg_tcdefine instead of
fg_tcmask to make colors 1 and 9 transparent by replacing the call to
fg_tcmask with the following:
fg_tcdefine(1,1);
fg_tcdefine(9,1);
Chapter 11: Block Transfer Routines 269
If you don't call fg_tcmask or fg_tcdefine, the fg_tcxfer routine considers no
colors transparent.
Transparent Block Transfers for Virtual Buffers
Fastgraph's fg_vbtcxfer routine transfers blocks with transparent colors
from the active virtual buffer to the active video page. Its arguments the
same as those of fg_vbpaste, but it does not copy any pixels whose colors are
transparent. The fg_tcdefine or fg_tcmask routines define which colors are
transparent, as when using fg_tcxfer.
Example 11-9 achieves the same result as example 11-8, but it does so
using virtual buffers. Rather than create a full-screen virtual buffer,
however, this example creates a virtual buffer one-fourth the screen size and
transfers the virtual buffer contents to each quadrant of the visual page in
four separate operations. In the upper left quadrant, we simply call
fg_vbpaste to display the virtual buffer contents. The three fg_vbtcxfer calls
fill the other quadrants, but with color 9 pixels being transparent. This
sequence of block copy operations from the virtual buffer creates the same
resulting display as example 11-8. Note that this example uses fg_tcdefine to
make color 9 transparent; we could just as well have used fg_tcmask.
Example 11-9.
#include <fastgraf.h>
#include <stdio.h>
#include <stdlib.h>
void main(void);
#ifdef FG32
char buffer[16000];
#else
char far buffer[16000];
#endif
void main()
{
int handle;
int new_mode, old_mode;
fg_initpm();
new_mode = fg_bestmode(320,200,1);
if (new_mode < 0 || new_mode == 12) {
printf("This program requires a 320 ");
printf("x 200 color graphics mode.\n");
exit(1);
}
old_mode = fg_getmode();
fg_setmode(new_mode);
fg_vbinit();
handle = fg_vbdefine(buffer,160,100);
fg_vbopen(handle);
fg_setcolor(7);
270 Fastgraph User's Guide
fg_fillpage();
fg_setcolor(9);
fg_locate(6,6);
fg_text("quadrant",8);
fg_vbpaste(0,159,0,99,0,99);
fg_waitkey();
fg_tcdefine(9,1);
fg_vbtcxfer(0,159,0,99,160,99);
fg_vbtcxfer(0,159,0,99,0,199);
fg_vbtcxfer(0,159,0,99,160,199);
fg_waitkey();
fg_vbclose();
fg_setmode(old_mode);
fg_reset();
}
Transferring Blocks to and from Conventional Memory
The final two block transfer routines we'll discuss are fg_getblock and
fg_putblock. The fg_getblock routine transfers a rectangular region from the
active video page or virtual buffer to an array (you can use fg_imagesiz to
determine the array size needed to store the block). The fg_putblock routine
transfers a block previously retrieved with fg_getblock to the active page or
virtual buffer. While these two routines are faster than fg_getimage and
fg_putimage, they are not as fast as fg_restore, fg_save, and fg_transfer.
Each of these routines requires five arguments. The first is the address
of the array that will receive or that contains the block. The remaining four
arguments define the position of the block on the active page or virtual
buffer, in the order minimum x, maximum x, minimum y, and maximum y. In text
modes, the coordinates are expressed as character space quantities (rows and
columns). In graphics modes, they are expressed as screen space values
(pixels), with the x coordinates extended to byte boundaries if required.
Note that both fg_getblock and fg_putblock expect the array address to be
passed by far reference except in BASIC. This means real mode Pascal programs
must use the GetMem procedure to allocate storage for the buffer, as this is
the only way to pass something by far reference in real mode Pascal. In 16-bit
environments, the maximum size of a block is 64K bytes, regardless of which
compiler you're using.
Example 11-10 is similar to example 11-5 and shows fg_getblock and
fg_putblock in action in a 320x200 graphics mode. The program displays the
word "text" and retrieves it into a 32 by 8 pixel block. After a keystroke, it
displays the block 8 pixels below and 8 pixels to the right of its original
position. The size of the buffer was chosen to be 256 bytes to accommodate the
largest size required for a 32 by 8 block (which occurs in the 256-color
graphics modes). Note also how the source and destination horizontal block
extremes were chosen for byte boundary alignment in case fg_bestmode selected
a 16-color graphics mode.
Example 11-10.
Chapter 11: Block Transfer Routines 271
#include <fastgraf.h>
#include <stdio.h>
#include <stdlib.h>
void main(void);
#ifdef FG32
char buffer[256];
#else
char far buffer[256];
#endif
void main()
{
int old_mode, new_mode;
fg_initpm();
new_mode = fg_bestmode(320,200,1);
if (new_mode < 0 || new_mode == 12) {
printf("This program requires a 320 ");
printf("x 200 color graphics mode.\n");
exit(1);
}
old_mode = fg_getmode();
fg_setmode(new_mode);
fg_setcolor(9);
fg_text("text",4);
fg_getblock(buffer,0,31,0,7);
fg_waitkey();
fg_putblock(buffer,8,39,8,15);
fg_waitkey();
fg_setmode(old_mode);
fg_reset();
}
Summary of Block Transfer Routines
This section summarizes the functional descriptions of the Fastgraph
routines presented in this chapter. More detailed information about these
routines, including their arguments and return values, may be found in the
Fastgraph Reference Manual.
For all block transfer routines, Fastgraph extends the horizontal pixel
coordinates to a byte boundary when the routines are used in a graphics video
mode.
FG_COPYPAGE transfers the contents of one video page to another. The
pages may be physical, virtual, or logical video pages. If both pages are
logical pages, they must exist in the same type of memory. The fg_copypage
routine does not work with virtual buffers.
272 Fastgraph User's Guide
FG_GETBLOCK retrieves the block (for later display with fg_putblock) at
the specified position on the active video page or virtual buffer. In text
modes, the block extremes are defined in character space; in graphics modes,
they are defined in screen space.
FG_GETHPAGE returns the hidden page number, as defined in the most recent
call to fg_sethpage.
FG_PUTBLOCK displays the block (previously obtained with fg_getblock) at
the specified position on the active video page or virtual buffer. In text
modes, the block extremes are defined in character space; in graphics modes,
they are defined in screen space.
FG_RESTORE copies a block from the hidden video page to the same position
on the active video page. The fg_restore routine does not work with virtual
buffers.
FG_RESTOREW is the same as fg_restore, but the block extremes are
specified as world space coordinates. The fg_restorew routine does not work
with virtual buffers.
FG_SAVE copies a block from the active video page to the same position on
the hidden video page. The fg_save routine does not work with virtual buffers.
FG_SAVEW is the same as fg_save, but the block extremes are specified as
world space coordinates. The fg_savew routine does not work with virtual
buffers.
FG_SETHPAGE defines the hidden video page (used by fg_restore,
fg_restorew, fg_save, and fg_savew).
FG_TCDEFINE defines the transparent attribute of a color index for use
with the fg_tcxfer routine. This routine has no effect when used in a text
video mode.
FG_TCMASK defines which of the first 16 colors the fg_tcxfer routine will
consider transparent. This routine has no effect when used in a text video
mode.
FG_TCXFER copies a block from any position on any video page to any
position on any video page, excluding any pixels whose color value is
transparent. This routine has no effect when used in a text video mode and
does not work with virtual buffers.
FG_TRANSFER copies a block from any position on any video page to any
position on any video page. It is Fastgraph's most general block transfer
routine. The fg_transfer routine does not work with virtual buffers.
FG_VBCOPY copies a rectangular region from one virtual buffer to another,
or to a non-overlapping position within the same virtual buffer.
FG_VBTCXFER copies a rectangular region from the active virtual buffer to
the active video page, excluding any transparent pixels.
